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Whole-Body Vibrations When Riding on Rough Roads

Whole-Body Vibrations When Riding on Rough Roads



The overall aim of this study was to ascertain the seriousness of the problem of whole-body vibration when driving on roads; ”Is the road roughness such that it entails a health hazard and/or a road ...

The overall aim of this study was to ascertain the seriousness of the problem of whole-body vibration when driving on roads; ”Is the road roughness such that it entails a health hazard and/or a road safety hazard through its impact on drivers?”. Other objectives were to estimate the scope of the problem during non-frozen ground conditions, to examine the problems and potential related to measurement techniques and to point out the necessity of further research in this field.

The measurement data was collected when driving on 37 kilometres of National Highway No. 90 (Hw 90) and 21 kilometres of County Road 950 (Lv 950) in Västernorrland County. The road condition on the test stretches covered the entire range from very smooth (IRI20 = 0.43 mm/m) to very rough (IRI20 = 22.78 mm/m). Whole-body vibration was measured in compliance with the ISO 2631-1 (1997) standard “Evaluation of human exposure to whole-body vibration”. This was done on stretchers with patients in different types of ambulance and at different speeds, and on the floor and driver and passenger seats for seated occupants in some different truck configurations.

There are three main sources of vibration: road roughness, vehicle properties and driver behaviour (including choice of speed). The interpretation of the results supports the opinion that within reasonable variations in these factors, road roughness plays a considerably greater part than the other two. High-energy, multi-directional vibrations at many natural body part frequencies were found at the seats in trucks. This is serious due to the risk of resonance, meaning a greater reproduction of vibration in the parts of the body afflicted than at the surface from which the vibrations are transferred. Further, the study substantiates findings from earlier studies; i.e., that the high frequency of occupational diseases among commercial drivers, especially in the locomotor systems, is related to rough roads. This relationship is probably strongest in geographic areas where the road roughness level is high on a large percentage of the roads. Where the roughness was greatest, peak values were registered on ambulance stretchers that considerably exceed the level that completely healthy people are assumed to experience as ”extremely uncomfortable” by international standards.
During a 15-minute ride on a stretch of National Highway 90, the vibration level in one type of ambulance was high enough to pose a potential health hazard had a healthy person been exposed to it for as little as 10 minutes a day. It was shown that the vibration on the ambulance stretchers was as great as at the drivers’ seat in wheel loaders loading blasted rock, bulldozers clearing way in forests for new road construction, etc. Vibration problems are even greater in the spring due to seasonal frost damage related additional roughness.



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    Whole-Body Vibrations When Riding on Rough Roads Whole-Body Vibrations When Riding on Rough Roads Document Transcript

    • Publication 2000:31EWhole-body vibration when riding on rough roads A study 2000-05
    • Date Document designationHead Office 2000-05-15 (2002-03-08) Publ 2000:31EAuthorRoad Engineering Division.Contact person: Johan Granlund.TitleWhole-body vibration when riding on rough roads.Main contentAt rural highway speeds, road roughness is a source of undesirable dynamic forces and displacement inthe interaction between road, vehicle and human. These vibrations can cause a sense of discomfort, andit cannot be ruled out that they could impair the health and performance ability of both drivers andpassengers alike.A study has therefore been conducted on National Highway 90 and County Road 950, aimed at ascer-taining the seriousness of the problem of whole-body vibration during travel. The roughness index onthe test stretches varied from very good (IRI 20 = 0.43 mm/m) to extremely poor (IRI 20 = 22.78mm/m). Vibrations that affect vehicle occupants were measured in different configurations of movingtimber lorries and ambulances. A separate report published by Ingemansson Technology AB presents adetailed account of how the measurements were carried out and how the data was stored and analysed.Another separate report published by the National Institute for Working Life presents the findingsfrom an analysis of the effect on the human body of the vibrations recorded.This report is a summary of the study. It also contains an interpretation of the findings from collatingthe vibration measurement data with the data collected in connection with the routine annual road co n-dition surveys. There are three main causes of vibration: road roughness, vehicle properties and driverbehaviour (including the choice of speed). The results of this study support the opinion that, withinreasonable variations in these factors, road roughness has a far greater impact than the other two vari-ables. Further, the study substantiates that the higher frequency of injury, especially in commercial driv-ers’ locomotor systems (as been found in earlier studies), is related to rough roads. This correlation isprobably strongest in geographical areas where long stretches on a large percentage of the roads have ahigh IRI, i.e. in the so-called ”forest counties” of Norrland, Värmland and Dalarna in Sweden. Ridingthe roughest road stretches, peak values were registered on the ambulance stretchers with vibration levelsthat are considerably above levels that completely healthy people are considered to experience as ”ex-tremely uncomfortable”, as per an international standard on evaluation of human exposure to whole-body vibration.PublisherEnvironmental Department.ISSN 1401-9612Vägverket printers in Borlänge 2002.Picture of the ambulance on the cover is published with the permission of Anders Wiman AB, ambulancemanufacturer.PublisherNational Road Management Division.Key wordsRoads, pavement, roughness, texture, ride, vibrations, shock, dampening, natural frequency, resonance,dynamic forces, displacement, fracture mechanics, road grip, ride quality, stress, discomfort, performanceability, health, motion sickness, living environment, working environment, road maintenance, surfacingDistributor (name, postal address, telephone, telefax)Swedish National Road Administration, Butiken, Internal Services Division, SE 781 87 BORLÄNGE,Sweden+ 46 243-755 00, fax +46 243-755 50Head OfficePostal address Telephone TelefaxSE 781 87 BORLÄNGE + 46 243 - 750 00 +46 243 - 758 25
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E PrefaceThis is a report of a study that was co-financed by the Västernorrland County Council,SCA Forest and Timber AB, Själanders Åkeri AB (haulier) and the Environmental De-partment at the Swedish National Road Administration (SNRA). The project was initiatedby the SNRA subsequent to a survey of the problems associated with driving on roughroads. Further, the trend towards ”smoother roads” revealed in the SNRA’s annual IRI(International Roughness Index) measurements seemed questionable in view of the intensedissatisfaction revealed in road user opinion surveys. Particularly perplexing was the acutedissatisfaction with the ride quality amongst commercial drivers, primarily in the north ofSweden. Our interest was stimulated even more when interviewing hauliers and transportpurchasers in Västernorrland County. After having studied reams of literature containingthe key word ”vibration”, including reports on the impact of road roughness on driver per-formance, driver fatigue, reports on incubators in ambulances being badly shaken duringtransport, and the high frequency of health problems amongst commercial drivers, particu-larly in their locomotor systems, sufficient research material had been collected to warrantinvestment in this project.Kjell Ahlin, Licentiate in Engineering and employed at Ingemansson Technology AB wasresponsible for the surveys and analyses. Professor Ronnie Lundström of the National In-stitute for Working Life was in charge of examining the impact on the human body of ex-posure to those vibrations measured. The vibration data was collated with the SNRA’sexisting road surface condition data (collected through laser/inertial technology) by theundersigned. The ambulances were driven by Leif Leding, medical orderly, and the trucksby Hans Selin and Bengt Själander. Vibration measurements were conducted on non-frozen roads, to comply with the SNRA routine road surface condition surveys. It is im-portant to keep in mind that the vibration problem is considerably greater during the springthaw, when roads are still partially frozen and roughness even more pronounced.I would like to take this opportunity to express my sincere appreciation to those who pro-vided the financial backing for this project, as well as the persons mentioned above andtheir colleagues, as well as to my own fellow colleagues throughout the Swedish NationalRoad Administration.Finally, I would especially like to thank Kathleen Olsson at the SNRA International Secre-tariat, for making the English translation possible.Borlänge 15 May 20001Johan Granlund, MSc (Civil Engineering)Project Manager21Translation finished on 8 March 2002.2Translation comments: Johan Granlund is now leading road roughness profilometry operations within SNRA Consulting Services. KjellAhlin is now Professor at Blekinge Institute of Technology. Professor Ronnie Lundström is now head of the Biomedical Engineeringand Informatics Department at the University Hospital of Northern Sweden. 1(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Contents1 SUMMARY ........................................................................................................................................................ 42 READER INSTRUCTIONS ........................................................................................................................ 63 DEFINITION OF TERMS .......................................................................................................................... 74 BACKGROUND..............................................................................................................................................18 4.1 FROM PAST TO PRESENT.............................................................................................................................. 18 4.2 ROAD ROUGHNESS IN BRIEF ....................................................................................................................... 21 4.3 MONITORING OF THE ROAD CONDITION AT THE SNRA....................................................................... 23 4.3.1 Road roughness measurements........................................................................................................ 23 4.3.2 Road user opinion polls.................................................................................................................... 25 4.4 ANALYSIS OF ROAD ROUGHNESS ............................................................................................................... 28 4.5 TRANSMISSION OF VIBRATIONS THROUGH THE VEHICLE....................................................................... 29 4.6 W HOLE-BODY VIBRATION.......................................................................................................................... 31 4.6.1 Natural frequencies and resonance in the human body............................................................... 32 4.6.2 Examples of the effect of whole-body vibration in the 0.5-80 Hz range..................................... 33 4.6.3 Examples of the effect of extremely low frequency whole-body vibrations ................................ 33 4.6.4 Origin of whole-body vibration...................................................................................................... 34 4.6.5 Measurement of whole-body vibration........................................................................................... 365 METHOD ........................................................................................................................................................ 38 5.1 TEST STRETCHES .......................................................................................................................................... 38 5.1.1 National Highway No. 90............................................................................................................... 38 5.1.2 County Road 950.............................................................................................................................. 39 5.2 VEHICLES ...................................................................................................................................................... 40 5.2.1 Ambulances ....................................................................................................................................... 40 5.2.2 Heavy trucks...................................................................................................................................... 41 5.3 MEASUREMENT AND ANALYSIS OF WHOLE-BODY VIBRATIONS............................................................. 44 5.3.1 Variables ............................................................................................................................................ 44 5.4 E XPERT ANALYSIS OF THE EFFECT OF VIBRATION ON THE HUMAN BODY........................................... 46 5.5 COLLATION BETWEEN THE VIBRATION DATA AND THE DATA FROM THE ROAD CONDITION SURVEYS ................................................................................................................................................................... 46 5.5.1 Effect of emergency action, ”the devil’s choice”, on National Highway 90............................... 466 RESULTS ......................................................................................................................................................... 49 6.1 ROAD SURFACE CONDITION AS PER THE SNRA’S ”PMS” DATABASE ................................................... 50 6.1.1 Roughness expressed as International Roughness Index............................................................... 50 6.1.2 Crossfall.............................................................................................................................................. 52 6.1.3 Lane cross-sections............................................................................................................................. 53 6.1.4 Seasonal variation in road roughness, County Road 950 ........................................................... 54 6.2 CAB ACCELERATION MODEL AS A FUNCTION OF ROAD ROUGHNESS (IRI).......................................... 557 DISCUSSION.................................................................................................................................................. 58 7.1 ROAD STRETCHES WHERE THE ROUGHNESS PRESENTS A HEALTH HAZARD........................................ 59 7.2 VARIATIONS IN THE ROAD CROSSFALL ARE PARTICULARLY HAZARDOUS ............................................ 64 7.3 METHODS TO REDUCE WHOLE-BODY VIBRATION IN CONNECTION WITH ROAD TRANSPORT .......... 67 7.3.1 Changed travel speeds....................................................................................................................... 67 7.3.2 Changes in vehicles ........................................................................................................................... 69 7.3.3 Road maintenance............................................................................................................................ 70 7.3.4 Does the choice of road maintenance strategy matter? ................................................................ 71 7.4 CONCLUSIONS .............................................................................................................................................. 72 7.4.1 Evaluation of impact on humans of vibrations related to road roughness ............................... 72 7.4.2 Assessment of the need to take action on the road network, etc.................................................. 72 7.4.3 Need for further research and development................................................................................... 748 REFERENCE LIST...................................................................................................................................... 75 2(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EIntroductionApart from the direct impact road roughness and texture has on vehicles and the environ-ment, these road characteristics are also an indirect source of the noise, infrasonic soundand whole-body vibration that cause stress on road users. The effect of this stress/load canbe divided into the following three categories, for which criteria can be stipulated and well-motivated limits set: 1. discomfort 2. performance ability 3. health impactThe effect on the human body depends on the type of load. It varies from individual toindividual, depending on the person’s own particular situation. Reactions can be acute (likespeech impairment), gradually increase during travel (like motion sickness) or steadily de-velop over time (like spinal injury). The effects can be transient, as in temporary visual im-pairment, or chronic as in kidney damage. Temporary exposure can cause stress reactions,like a faster pulse or higher blood pressure, which in turn entails a greater stress on theheart. Sustained exposure can tire the brain a nd produce drowsiness. Daily exposure can, inthe long run, impair health and result in long periods of sick leave or even early retirement.Sometimes these ailments can require medical treatment, which in turn can have side ef-fects that can substantially impair quality of life. Musculo-skeletal injury is by far the great-est working environment problem in the Western world today.In the mid 1970’s, the exposure of truck drivers to vibration was an issue raised at the fed-eral government level in the USA, formulated as ”Do vibrations (as well as noise, toxicfumes and other factors that contribute to truck “ride quality”) have a negative effect ondriver health and on highway safety?” A research programme that extended over severalyears, ”Ride Quality of Commercial Motor Vehicles and the Impact on Truck Driver Per-formance” was initiated in 1977 to answer this question. The findings were summarised ina report published in 1982 entitled ”Truck Cab Vibrations and Highway Safety” [66]. Thisreport was jointly produced by leading researchers, road authorities, vehicle manufacturers,hauliers and commercial drivers. It shows that the answer to the key question as to whetherthere is any correlation between cab vibrations and road safety is YES, that there is goodreason to believe that vibrations affect drivers’ health, and that vibrations must be elimi-nated at source through effective road maintenance rather than merely dampened. Thereport concludes that if the deterioration of the road network is allowed to continue, theresult will be serious health and road safety problems.Today, further on down the road, we can see how the American road network has beenupgraded. According to the FHWA report Life-Cycle Cost Analysis in Pavement Design,action is nowadays initiated on federal roads before the condition reaches a level corre-sponding to IRI 2.7 mm/m [67 ]. In the study conducted during summer on Swedish Na-tional Highway 90, IRI1 values close to 100 mm/m have been measured3, 37 times abovethe American limit. Hw 90 is known to be much rougher during the spring thaw.At the time of writing, an EC directive stipulating limits for exposure to whole-body vibra-tion based on health and safety criteria is in the process of being drawn up.3 Laser/inertial Profilometers have limitated laser measuring range (MR). On the Profilometers used in Sweden MR for vertical distanceis +/ - 100 mm. Since the distance from the laser beam to the front axle of the Profilometer vehicle is close to 1 m, profile slopes (usedwhen calculating IRI) will begin to be underestimated when they exceed about 100 mm / 1 m = 100 mm/m in static theory case. Inpractise, Profilometer pitch and roll dynamic motion reduces this range of use further. 3(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E1 SummaryThe overall aim of this study was to ascertain the seriousness of the problem of whole-body vibration when driving on roads; ”Is the road roughness such that it entails a healthhazard and/or a road safety hazard through its impact on drivers?”. Other objectives wereto estimate the scope of the problem during non-frozen ground conditions, to examine theproblems and potential related to measurement techniques and to point out the necessityof further research in this field.The measurement data was collected when driving on 37 kilometres of National HighwayNo. 90 (Hw 90) and 21 kilometres of County Road 950 (Lv 950) in Västernorrland County.The road condition on the test stretches covered the entire range from very smooth (IRI20= 0.43 mm/m) to very rough (IRI20 = 22.78 mm/m). Whole-body vibration was measuredin compliance with the ISO 2631-1 (1997) standard “Evaluation of human exposure towhole-body vibration”. This was done on stretchers with patients in different types ofambulance and at different speeds, and on the floor and driver and passenger seats forseated occupants in some different truck configurations.There are three main sources of vibration: road roughness, vehicle properties and driverbehaviour (including choice of speed). The interpretation of the results supports the opin-ion that within reasonable variations in these factors, road roughness plays a considerablygreater part than the other two. High-energy, multi-directional vibrations at many naturalbody part frequencies were found at the seats in trucks. This is serious due to the risk ofresonance, meaning a greater reproduction of vibration in the parts of the body afflictedthan at the surface4 from which the vibrations are transferred. Further, the study substanti-ates findings from earlier studies; i.e., that the high frequency of occupational diseasesamong commercial drivers, especially in the locomotor systems, is related to rough roads.This relationship is probably strongest in geographic areas where the road roughness levelis high on a large percentage of the roads. Where the roughness was greatest, peak valueswere registered on ambulance stretchers that considerably exceed the level that completelyhealthy people are assumed to experience as ”extremely uncomfortable” by internationalstandards.4 seat, seat back, floor, stretcher 4(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Vibration 2(weighted acceleration [m/s ])on stretchers, and in the case of the bulldozer, at the operator’s seat. Some studies indicate that exposure to vibrations of 1.6 2 1.30-1.35 m/s for 10 1.4 minutes a day can be harmful even for healthy 1.2 people. The journey by 1 ambulance on the rough stretch of highway took a 0.8 little more than 15 minutes. 0.6 Clearing forest for new road construction, bulldozer 0.4 CASE 1150 C 0.2 Mobile Intensive Care Unit Ambulance 0 Emergency Ambulance Rough road, IRI average = 4.0 mm/m Smooth road, IRI average = 1.2 mm/mDuring a 15-minute ride on a stretch of National Highway 90, the vibration level in onetype of ambulance was high enough to pose a potential health ha zard had a healthy personbeen exposed to it for as little as 10 minutes a day. It was shown that the vibration on theambulance stretchers was as great as at the drivers’ seat in wheel loaders loading blastedrock, bulldozers clearing way in forests for new road construction, etc. See the figureabove. Vibration problems are even greater in the spring due to seasonal frost damage re-lated a dditional roughness. 5(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E2 Reader instructionsThe project is presented in three separate reports:1. The first is a technical analysis of the whole-body vibrations measured in trucks and ambulances. This report was compiled by Kjell Ahlin, Licentiate in Engineering at In- gemansson Technology AB [64], and may be of interest for researchers etc.2. The second analyses the impact on the human body of the vibrations measured. This report was compiled by Professor Ronnie Lundström at the National Institute for Working Life [65]. A summary of the conclusions is presented in Chapter 7. The report is available (in Swedish) at SNRA as well as NIWL websites, using the following links: http://www.vv.se/aktuellt/pressmed/2000/VVRapport.pdf or http://umetech.niwl.se/Published/.Publ.html3. The third is the report at hand, compiled by Johan Granlund, MSc (Civil Engineering), of the Swedish National Road Administration. This report presents the results from collating the data collected in the annual road condition surveys with the whole-body vibrations measured on the test stretches. It also compares the results with the ISO limits for whole-body vibrations, and assesses the magnitude of the problem on the state network. This report is available on the SNRA website, using the following link for the Swedish version http://www.vv.se/publ_blank/bokhylla/miljo/2000_31/intro.htm and this link for the English version http://www.vv.se/for_lang/english/publications/index.htm 6(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E3 Definition of termsThe definitions of the following terms are based on those in the Swedish National Enc yclopaedia [1] with itsappurtenant dictionaries [34], the Swedish Centre for Technical Terminology glossaries [9], EngineeringMechanics [40], Handbook of Human Vibrations [11], Vägtrafikteknisk nomenklatur (Highway Engineer-ing Terminology) [16] published by the Transport Research Institute and ASTM´s Terminology Relating toVehicle-Pavement Systems [20]Accident frequencyNumber of accidents at a certain intersection, stretch or unit of distance. Differences in the accident ratio between two road networks show that one is ”more dangerous” for an individual than the other. Differences in acci- dent frequency between two road networks depends partially on the differ- ence in the accident ratio, and partially on the difference in the number of vehicles using the road networks. A simple way to reduce the accident fre- quency on a road with heavy traffic volume is to divert certain parts of traf- fic to other smaller roads. However, as the accident ratio is generally higher on smaller roads, this would increase the total number of accidents. From this perspective, the accident ratio is better than the accident frequency for assessing how dangerous roads are. The road network in Jämtland County (known to have low traffic volumes but poor roads) has the highest accident ratio in Sweden.Accident ratioNumber of accidents related to units of measure in traffic; i.e., the term vehicle kilometresis the unit commonly used on road stretches. At junctions the unit of measure is the num-ber of vehicles entering the intersection.AccuracyThe ability of the measurement instrument to give results close to the true value for theparameter measured. The greater the accuracy, the less the error.AlignmentThe design of the road profile in space.AmplitudeAmplitude is the maximum deviation from the mean of a signal (e.g., road roughness, orvibration), see Figure 10.ComfortA subjective state of well-being or absence of mechanical disturbance in relation to theinduced environment (mechanical vibration or repetitive shock). 7(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EAgreeable and practical convenience {relaxed conditions under which to live and work}. Comfort connotes the absence of significantly disturbing or intrusive physi- cal factors. It is a complex subjective entity depending upon the effective summation all the physical factors present in the induced environment, as well as upon individual sensitivity to those factors and their summation, and such psychological factors as expectation. (For these reasons, for example, the same values of vibration that might be judged by most riders to be un- comfortable in a limousine may be judged acceptably comfortable in a bus.)The main factors behind comfort reduction (discomfort) are shown in Figure 9. 8(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31ECrest factorThe ratio between the frequency-weighted peak value and the frequency-weighted rootmean square for the parameter studied. See Figure 3.CriteriaA criterion is a verbal description of the effect, e.g. discomfort, reduced performance abilityor physical injury that is of interest. Limits (threshold values, target values, etc.) are set toensure an acceptably low probability of the effect that the criterion defines. In other words,the criteria explain the reasons for the different limits.CrossfallThe angle between the horizontal plane and the surface of the roadway, carriageway orshoulder, measured at a right angle to the longitudinal direction of the road.ErgonomicsStudy of the relationship between people and their work environment, especially theequipment they use. See also [52].Estimated vibration dose value, eVDV)An estimation of a cumulative measure of the vibrations and shocks that a person is ex-posed to during the period under study, based on the frequency-weighted root mean squarefor the vibration. See Formula 1. If the vibration level varies or contains shock elements, the vibration dose value must be determined directly from the complete measurement series. This is usually the case when the crest factor exceeds 6 – 9, which makes eVDV less useful for ride quality assessment on the rougher roads.eVDV = 1.4 * a rms * T1/4Formula 1 Estimated vibration dose value during exposure time TFracture mechanicsThe science of how solid material breaks. This is often characterised by one or more cracksspreading throughout the mass of a structure, ultimately resulting in its splitting into two ormore parts. Cracks can increase through different mechanisms, like fatigue. An increase infatigue occurs in structures exposed to repeated load. The increase can be very little at anyindividual load. However, major cracks can form in a very short time through exposure tovibration. The research that laid the foundation for fracture mechanics was carried out dur-ing the Second World War. Since the 1950’s, fracture mechanics has developed into animportant element in the mechanics of materials. Most research has been conducted in theUSA and has been motivated by safety demands, primarily within the nuclear power andaviation industries. Fracture mechanics can be used to answer the question ”how quicklydoes a small crack grow through fatigue at the load spectrum to which the structure is ex-posed?”.HealthA condition of complete physical, psychological and social well-being, and not only theabsence of illness or disability [World Health Organisation (WHO), 1946]. 9(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EHorizontal curveThe curve indicating the direction of the road alignment in the horizontal plane.International Roughness IndexThe IRI value is a substitute measure for the vertical vibration that occurs in the suspen-sion of a model (”the Golden Car”) of a quarter of a standard passenger car during a hypo-thetical journey at the speed of 80 km/h on the road stretch studied. The value describesthe accumulated vertical displacement between the car body and the non-suspended massof the wheel, divided by the distance travelled. The unit of measure for the IRI is [mm/m],which is low when the road is smooth along the wheel track5 in which the roughness pro-file is measured. The IRI is currently the preferred unit of roughness measure used in Swe-den and many other countries around the world that conduct objective surveys of the roadcondition. Index notation such as IRI 400, IRI 20, IRI 1 etc is used when explaining the length of report/averaging interval, such as 400 metre, 20 metre and 1 me- tre. Up until now, the basic report storage interval in the SNRA PMS has been 20 metre. (As a comparison; the sampling spatial frequency used by ve- hicle manufacturers fatigue researchers typically must be no longer than about 1 decimetre, not to lose information about shock that causes damage).JerkThe first time-derivate of acceleration. Jerk is thus a measure of how fast the magnitude ofthe acceleration changes. When assessing damage potential, the relation between load and bearing ca- pacity is studied. The “bearing capacity” of the human body depends strongly of the state of muscular brace, comparable to the case where a small child is learning to stand and walk. When exposed to unexpected occasional shock, an intensive jerk may reduce the chance for the body to suddenly increase its “bearing capacity” through instinctive brace. This implies that among differ- ent motions with a similar peak acceleration, motions having a more inten- sive jerk may be more serious than those with a less intensive jerk.5 In Sweden, the IRI value is measured in the outer wheel track as seen from the centre of the road. In some countries, it is measuredfrom a mean profile of the outer and inner wheel tracks instead. 10(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31ELimitsThe value stating the maximum permitted limit for a source of discomfort or injury. A limit is generally only set for activities that are planned and governed by directives issued by public authorities. The general trend in most countries is towards reducing limits. It is usually the authority responsible for a specific field of expertise that sets these limits. The health and hygienics limits are particularly important in the work environment. A health and hygienics limit is not a sharp line between harmful and non- harmful exposure. In Sweden health and hygienics limits have a legal status. See also the Swedish Environmental Code (SFS 1998:808) and the Health and Safety at Work Act (SFS 1977:1160). 11(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EMacrotextureTerm for those aberrations in the road surface (compared to an ideal plane) that have cha r-acteristic wavelength and amplitude dimensions from 0.5 mm and upwards to those thathave no effect on the interaction between tyre and roadway.Measurement errorDifference between the measurement value a nd the true value.Measurement resultsThe product of the measurement value and the unit of measure. The measurement valuecan have been corrected in connection with this through calibration in order to take knownsystematic errors into consideration.Measurement valueThe value for the parameter compared to the unit of measure. Can be identical with themeasurement result.Motion sicknessA physiological reaction in people induced by vibration, where the central nervous systemis incapable of co-ordinating information obtained visually, from the balance organ in theear and from joints and muscles. The reaction can cause drowsiness and affect perform-ance ability. Symptoms include greater salivation, perspiration, depression, apathy, pallor,nausea, dizziness and vomiting. Motion sickness seldom occurs in connection with vibra-tions with a higher frequency than 0.5 Hz. When the reaction occurs in a moving vehicle, itis usually called ”travel sickness”. The most renowned hypothesis for a qualitative explanation for the origin of motion sickness is called ”the sensory conflict hypothesis”[36]. A schematic dia- gram of this hypothesis is shown in Figure 1. Several other conflict hypotheses are discussed in Griffins ”Handbook of Human Vibrations” [11]. 12(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Stimuli Receptors Central Nervous System Responses Active Motor controlmovement Volitional system and reflex move- ment Eyes Updates internal Internal model model (adaption) Semicir- neural store of Motion cular expected signals stimuli canals Otoliths Leaky Neural centre Motion and other Compa- integ- mediating signs sickness gravi- rator & symptoms of symptom ration receptors motion sickness Passivemovement Mismatch signal Threshold Figure 1 Schematic diagram of the sensory conflict hypothesis. This figure has been modified by Förstberg [36], originally developed by Benson (1988). Natural frequency The most fundamental property of an oscillating system. Natural frequency constitutes the free oscillation frequency of a system after having been disturbed. Every real system has several natural frequencies, and each of these has a given pattern of movement. When a system is subjected to an external disruptive (driving) force whose frequency is equal to a natural frequency in the system, resonance occurs and the magnitude of the vibration in- creases. See Figure 2. 13(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 2 Mechanical model of the human body specifying natural frequencies for a few parts of the body [51]. Observe that the body lacks the female bosom. The natural frequencies refer to vibrations in the axial direction of the body parts (e.g. the spinal column) 14(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EParameterA characteristic that is the object of measurement.Pavement Management Systems, PMSA system that in an organised, co-ordinated way manages the road administration process.Peak valueThe maximum deviation from the mean of a parameter during a given interval. See Figure3. The peak value is used especially when assessing the risk of mechanical damage frommotion/force sequences of short duration - shock.PrecisionThe degree of agreement between a number of values measured, determined through re-peated measurements. Precision has nothing to do with the deviation of the values ob-tained from the true values for the parameter. Precision is sub-divided into repeatabilityand reproducibility.RepeatabilityThe precision of the values measured for a given parameter, determined in a uniform wayand under similar conditions.ReproducibilityThe precision of the values measured for a given parameter, determined in a uniform waybut under different conditions, such as another measurement method, another operator,another instrument or another point in time.ResonanceGeneral phenomenon in oscillating systems implying that even a weak intermittent externaldisruption (driving force) within a narrow frequency range can result in a large increase inthe oscillation amplitudes, accelerations and energy content of the system. This increasedepends on the frequency and becomes maximal when the frequency is largely equal to thefree natural frequency of the system. Through resonance, large amounts of energy can betransferred by the driving force to the oscillating system, in connection with which damageor disruptions in operation often occur. This phenomenon is of key importance from asafety perspective, etc.Road alignmentThe (imagined) large scale vertical and horizontal curvature of a road.Road roughnessTerm used for deviations in a road surface compared to a real plane, which affect vehiclemovement, ride quality, dynamic loads, drainage and winter maintenance.RoadwayCarriageway including the shoulders.RollMovement of rotation around the x-axis. See Figure 24. 15(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31ERoot mean square, rmsThe root mean square of a variable during the period studied. See Formula 2 and Figure 3. When assessing ride quality, effects of occasional shock are often of great in- terest. The running root mean square of the weighted acceleration (using in- tegration time 1 s) is then often the preferred definition of vibration, since this definition has been proven to correlate very closely with perceived an- noyance [75]. To assess the risk of mechanical damage to the spine, the weighted positive (compression phase) peak acceleration is the preferred defi- nition. t2 ∫ a (t ) 2 dta rms = t1 t 2 − t1Formula 2 Root mean square for accelerationRoot sum of square, r.s.s.A summation procedure for vectors in different directions. For the root meansquare, the square root is taken from the sum of the vectors squared root meansquares.Running rmsA filtering procedure that smoothens a very transient measurement series (as where occa-sional shocks have occurred) that have a high crest factor.Second Law of NewtonThe acceleration of a particle is proportional to the force acting upon the particle and oc-curs in the direction of that force. Normally expressed in dynamic analysis as F = m*a.StressThe physiological/hormonal reactions in the organs of the body that are triggered byphysical and mental ”stress factors”. Threatening or strenuous situations stimulate in-creased secretions of adrenaline and noradrenaline. These hormones function such thatthey increase the heart rate, blood pressure and circulation of blood to the skeletal muscles,while decreasing the circulation of blood to other organs. Further, breathing is stimulated,the trachea expand and the level of sugar and fatty acids in the blood increases. When peo-ple are unable to control their own situation, the cortisol level also increases substantially.Cortisol increases the amount of glucose in the blood, as well as the turnover of fats andproteins. These and some 1400 other reactions to stress mean that the body, through all itsendeavours to adapt to the situation, is prepared to destroy itself after being subjected to anall too extended or strenuous load.SurveyA series of measures to determine the value of a parameter. 16(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EUnit of measureReference value for a parameter; e.g., in the case of distance, a metre could be used as aunit of measure.VibrationOscillation in mechanical systems, where parts of the human body and human organs canbe included. (See Figure 2). This is governed by different kinds of force: mass, restoration,calming and disruptive (driving, instigating) forces. Vibration can be measured in terms of displacement, speed or acceleration. The unit of measure used for acceleration is [m/s2]. Results are usually pre- sented as peak values (mechanical spinal damage etc) or as a root-mean-square or running root-mean-square (perceived ride quality etc). See Figure 3. Peak value Root mean square Mean value Mean valueFigure 3 Peak value, root mean square and mean value for a signalVibration dose value, VDVA cumulative measure of the vibrations and shock elements to which a person was exposedduring the period under study. See Formula 3. t2VDV = 4 ∫ a w (t ) 4 dt t1Formula 3 Vibration dose value for accelerationWavelengthThe shortest distance between two of the signal’s points with an equal phase. See Figure10. 17(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E4 BackgroundTo most people, a roadway is merely a charcoal grey surface of infinite length. They expectit to provide safe driving conditions, a smooth and quiet ride, minimal splash and spraywhen it is raining, good visibility during poor conditions and that it will last a long time (toavoid disturbance from road works).A closer examination of the road reveals that it has several important characteristics, suchas surface texture. Texture is needed to provide road grip, minimise spray and mist when itis raining, and reduce the glare from high beams at night. But the texture can cause morenoise as well as reduce the life span of both roads and tyres. As the road surface ages and isworn down by studded tyres, heavy vehicle loads and climate, road damage begins to a p-pear. Deformation (or road roughness), which is one type of damage, can limit bothshorten the life span of a road as well as reduce the quality of the ride. Roughness, primar-ily longitudinal, can also be built into the road from the outset due to poor geometric de-sign/construction.Roughness is the source of many kinds of irritation that road users encounter; flickeringheadlight reflections, deep pools of water, the dynamic forces that increase pavement stressand damage to vehicles and cargo, and poor ride quality. Most road users are very sensitiveto ride quality, making this a prime criterion when setting road maintenance priorities [68].Road roughness can mean reduced travel speeds. This has led many to believe that roughroads are safer than smooth ones, since speed is generally acknowledged as dangerous.However, after collating databases with information on accidents, road surface condition,climate, road geometry, speed, etc at VTI (Swedish Road & Transport Research Institute),it was concluded that ”the accident ratio increases with an increase in the roughness” and”roughness has a major impact” [18]. A strong correlation between road roughness and theaccident ratio on the paved part of the state road network in Sweden has thus been ascer-tained, implying that the idea of rough roads being safer is probably a serious misconcep-tion.However, such a statistical correlation is not clearly tantamount to the accident risk actuallybeing caused by roughness. For instance, it is likely that the vehicles on the roads in ruralareas, where roughness is worst, are older and less roadworthy than those found on thesmoother roads in and between the larger cities. It is therefore necessary to verify a statisti-cal correlation through experiments that provide information about possible mechanismsfor an actual cause and effect relationship. This could include the effect of roughnessthrough mechanical interference on the steering and braking properties of road vehicles,the effect on winter road maintenance and on drivers’ performance ability.4.1 From past to presentThe mechanisation of human transport on roads has taken place in a very short time. Peo-ple were still basically travelling on the backs of animals or on foot in the 18th century,despite the fact that the invention of the wheel 3 500 years before Christ had made thedevelopment of animal-drawn carts possible. The reason was that roads were often almostentirely impassable, which explains why the carts were primarily used to transport goods,and even then only at average speeds up to about 10 km/h. This meant that travellers usu- 18(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31Eally experienced more discomfort from dirt than from vibrations. On the narrow streets ofStockholm, the upper class avoided the dirt by being carried on palanquins. A tariff for thiswas laid down in 1726 [58].Through Carl Snoilsky’s classical poem on Stenbock’s courier, generations of Swedish stu-dents have learned about how Captain Henrik Hammarberg, who was sent off by GeneralMagnus Stenbock from Helsingborg with a message to the king and government in Stock-holm on February 28th 1710, rode so hard that ”a horse collapsed behind him at everystation”. Modern historians maintain, however, that the courier, who covered the journeyof 900 kilometres at an average speed of 18 km/h, probably did not ride on horseback atall. Verification ”Folio 2282” in the 1710 treasury records (preserved in the National Ar-chives) for Hammarberg’s travelling-expenses account clearly shows that he travelled by acarriage drawn by a team of horses from station to station. It is believed that he sufferedfrom travel sickness during the journey; ”this coach is swaying so frightfully on these terri-ble roads” [59].The bicycle could enter the scene at the turn of this century, as a result of the soft non-bituminous roads, which could be evened out by simple means as needed. Bicycles werecrowded further and further out to the periphery as motoring became more widespread. Inthe past 130 years, mobility for people in Sweden has grown a thousand fold. See Figur 4. Mobility trend in Sweden, 1850 - 1990 50000 45000 40000Decade Travelled distance [m] 35000 1850 40 30000 1870 200 25000 1890 350 20000 1910 900 15000 1930 3000 10000 1960 20000 5000 1980 40000 0 1850 1870 1890 1910 1930 1950 1970 1990 DecadeFigur 4 The average daily distance travelled by vehicle by adults in Sweden from the 1850’s to the 1990’s. Data in the tables extracted from [61], supple- mented in the figure with data from [62].Roads became steadily harder throughout the years, necessitating more sophisticated careand maintenance routines. The long distances covered at the high speeds that characterisemodern road traffic, mean an exposure to vibration and shock that, in the presence of sig-nificant road roughness, can mean people being exposed to mechanical energy that is sub-stantially higher than at any other time in history. According to the second law of Newton,the magnitude of this mechanical load can be estimated through measuring the accelerationof whole-body vibration. 19(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EThe mental stress is more difficult to measure. At the macro level, it has been shown thatthe risk for certain types of cardio-vascular disease in Sweden is more than three timeshigher for commercial drivers than for the average worker. Mental stress under certaindriving conditions is considered to explain the raised level of stress hormones found incommercial drivers, and is believed to cause the problem [69, 70].Amongst older commercial drivers, musculo-skeletal problems and cardiovascular diseasesare the primary reasons for changing their occupation [71]. 20(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E 4.2 Road roughness in brief Road roughness can result from faulty basecourse adjustment (usually through insufficient repair of crossfall variations or longwave deformations); incorrect initial construction; post- compaction of added layers; subgrade settlement; material abrasion -- primarily by studded tyres -- or through uneven frost heave during the spring thaw. A general rule, based on laboratory tests, is that drained road structures can stand being driven on by trucks six to seven times more than those without drainage before unaccept- able deformation occurs in the unbound layers. Ditching is thus a very effective mainte- nance measure for preventing roughness, if it is executed so that the gradient of the inner embankment is not steeper than 1:3 (otherwise there is the risk of edge deformations due to insufficient lateral counterstay). A drained road structure is also a prerequisite for avoid- ing frost-related roughness in winter. The binder stiffness affects the ability of the asphalt to distribute the load and thus the risk of deformation in underlying layers. Temperature is a key factor for this stiffness, which means that dark asphalt roads become rough faster than those with a light surface. The mechanical properties of vehicles can also increase roughness. As early as in the 1930’s, a large-scale experiment showed a substantial increase in roughness on gravel roads when the test vehicles had high-pressure tyres, while there was not even enough roughness to measure when low-pressure tyres were used (the roadway had actually been smoothed out). Speed and suspension were also shown to be major factors affecting roughness [56]. These conclusions could even be valid today for roads with a thin surface, like single sur- face treatment (Y1G), which is very similar to the dust abatement measures undertaken on the old gravel road. 8,00 7,00 6,00 5,00IRI [mm/m] 4,00 3,00 2,00 1,00 0,00 01 01 -01 -01 -01 -01 -01 -01 -01 -01 -01 -01 1- 0- -12 -03 -06 -09 -04 -07 -02 -05 -08 -11 -0 -1 00 00 00 00 00 00 00 00 00 00 00 00 Tid på året Figure 5 Conceivable variation in roughness per month, on a specific road sec- tion 21(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31ERoad roughness varies throughout the year, which often is more noticeable than the annualdeterioration in the road condition. An estimation of what the variation might be like overthe year on a road that is not treated with salt de-icer and that is slightly frost-damaged isshown in Figure 5. Variable weather conditions in addition to winter maintenance measuresaccounts for the greater variation shown in the graph for the winter months, while the ex-tremes in the spring are explained by the thaw. While there is a high rate of steadily increas-ing deterioration on roads with deficient bearing capacity and/or problems related to fro-zen ground conditions, the deterioration on well-constructed roads is minor and disappearsin time (except during the late stage when surface abrasion occurs if no preventive meas-ures are undertaken). Roughness can be eliminated through appropriate periodic mainte-nance. Road strengthening serves to reduce roughness immediately, while also retarding itsfuture speed of increase. Needless to say, this applies regardless of whether the improvedbearing capacity has meant a change in the administrative bearing capacity class of the road.For microtexture, as well as that part of the macrotexture with wavelengths shorter than ca25 mm, it is important that the road roughness amplitudes are neither too large nor toosmall. To a certain extent, this kind of roughness produces desirable effects; like friction,noise reduction, a certain amount of drainage, etc. Some effects are undesirable, like greaterwear and tear on tyres [2].All roughness with wavelengths above ca 25 mm increases transport costs [2]. It is possibleto correct roughness with amplitudes under ca 15 - 30 mm and with wavelengths up toabout 10 metres simply through a new wearing course. Roughness with larger amplitudes,or of a more longwave nature, is remedied through milling or more fill works. Frost-relatedroughness normally demands highly extensive and expensive measures, such as deep drain-age and extensive material replacement. The maintenance and repair budget (per squaremetre road surface) must therefore be several times higher for roads damaged by frost thanfor roads damaged by traffic. 22(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E4.3 Monitoring of the road condition at the SNRA Roads with an IRI > 5 mm/m 14% 12% 10% Northern Region Central Region 8% Stockholm Region Western Region 6% Mälardalen Region South-Eastern Region Skåne Region 4% 2% 0% 95 96 97 98 99 YearFigure 6 Development of severe roughness on the paved state road network, expressed as time series of IRI 20 > 5 mm/m per road management re- gion. A lower percentage indicates fewer very rough stretches on the road network.4.3.1 Road roughness measurementsThe SNRA regularly measures roughness on paved state roads using high technology sur-vey vehicles. European and National Highways are surveyed annually, and other roads atleast every third year. Up until now, the parameters that have been of greatest interest areruts, crossfall and roughness. The IRI value [mm/m] is the most important measure ofroughness, and is calculated from the road roughness profile measured. The IRI value canbe said to describe the vertical vibrations in the suspension of a mathematically simulatedpassenger car driving at a speed of 80 km/h, and is affected primarily by roughness withwavelengths between about 1 and 30 metres. IRI is very similar to the measures of rough-ness used in the USA as early as the 1920’s when roughness began to be measured usingsimple vehicles. These roughness measures were successfully used to stimulate competitionamong civil engineers and contractors to achieve better ride quality through their beingofficially published as objective comparisons of different road projects [54].Today’s survey results are analysed and interpreted as the basis for budget discussions, set-ting priorities, research projects, evaluating performance contracts, etc [8]. Figure 6 showsthe percentage of roads with excessive roughness (very high IRI values) in all road man-agement regions. Signs of improvement can be seen, particularly up to 1999. 23(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EHowever, an entirely different, negative trend was found when reviewing road users’ opin-ions on ride quality. See Section 4.3.2. The discrepancy between the results from the roadcondition and road user surveys can perhaps be attributed to the fact that people are travel-ling more (which can increase the exposure to vibration even if the road roughness is un-changed) and that the annual road condition surveys are only performed when there is noground frost, for reasons of measurement precision. Roughness on frozen roads can bemuch worse than on non-frozen roads, and ground frost conditions vary substantially fromyear to year. Much higher local IRI values have been measured on frost-damaged roads,than what has been registered in the routine surveys in the summer months.During the quality a ssurance of road condition surveys, it was observed how the vehicleoperators found it much more difficult on rough roads to follow the driving instructionrequirements. In other words, roughness has a strong adverse effect on driver performance[private comment made by Kerstin Svartling, administrator for the SNRA’s road conditionsurveys].The significance of different types of roughness and different speeds can be studied inFigure 7. 24(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 7 Typical vertical motions at the rear axle and in the car body when driv- ing at different speeds on different road roughness [12]4.3.2 Road user opinion pollsThe road user opinion polls conducted by the SNRA between 1995 and 1998 included 30000 people. The questions cover new roads, care and maintenance. On the whole, the find-ings were not too negative. The majority of the interviewees were satisfied in most respects,with one major exception being road roughness.The smoothest roads in Sweden are found in Skåne Region (southern Sweden). Despitethis, the percentage of commercial drivers in Skåne who are satisfied with ride quality onthe national road network is as low as 30 – 35 percent. The percentage of satisfied roadusers is much lower in other parts of the country and with respect to other types of road. 25(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EDissatisfaction is greatest and growing most rapidly in the northern half of the country. Forexample, it is expected that 0% (none) of the commercial truck drivers in the counties ofVästernorrland, Jämtland, Gävleborg and Dalarna (the Central Road Management Region,being part of “northern Sweden”) will be satisfied with the ride quality on regional thor-oughfares in the winter of 1999. See Figure 8. SNRA Central Region (Västernorrlands, Jämtlands, Gävleborgs och Dalarnas counties) Marks given by commercial drivers for the ride quality on regional roads Results 1996 Results 1997 8% 18% 82% 92% Percentage dissatisfied Results 1998 Percentage satisfied Prognosis 1999 0% 5% 95% 100%Figure 8 Commercial drivers’ marks for ride quality on regional roads. Väs- ternorrland, Jämtland, Gävleborg and Dalarna Counties [6].At the national level, the percentage of commercial truck drivers who are satisfied with thequality of the ride is about half that of passenger car drivers. However, even the percentageof passenger car drivers who are satisfied in this respect is low [6][37].Factors that are known to influence people’s sense of discomfort are shown in Figure 9. 26(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Texture Vibrations Vibration- Roughness related discomfort Alignment Jerky ride Vision disor- ders Megatexture Shock Difficulties in Roughness handling Noise and Sleeping disor- Roughness Infrasound ders Texture Visually Variance between Noisiness Roughness individuals Road signs Information Speech diffi-Road markings culties The individual Ride quality Rest areas Food / beverages Sweating / (sum of discomfort) freezing ? Odours Air quality Variance for the individual ? Temperature Glaring lights ? Body posture Uncomfortable posture ? Privacy Social discom- fort Disruptive Other Other road works Figure 9 Factors associated with road management that produce discomfort in connection with road transport. The figure has been modified on the basis of [11]. The figure also helps us understand for example that faulty, irregular crossfall, unsuitable texture and major road roughness cause many different kinds of discom- fort. Road damage, along with recurrent disruptive road works, thus results in poor ride quality. 27(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E4.4 Analysis of road roughnessThe deviation of the road surface from a horizontal plane can be described by the wave-lengths and amplitudes of the roughness, see Figure 10. The very shortest roughness wave-lengths are classed as microtexture, which is determined by the properties of the aggregateand binder in the surface. Somewhat longer wavelengths are classed as macrotexture,which is determined by such things as the shape of the aggregate and the particle size dis-tribution. Longwave deviations are quite simply designated as roughness [2], often causedby more or less extensive settlement, frost heave or ice lenses in or under the road struc-ture in the winter. λ A λ/2 AFigure 10 Wavelength (λ) and amplitude (A). Above at corrugation, below at a pothole.The basic relationship between travel speed (velocity) v [m/s], wavelength λ [m] and verti-cal vibration frequency f [s-1] is shown in Formula 5. Depending on the travel speed andtype of vehicle, vehicle properties are a key factor where the wavelengths are up to 25 - 50m. Where the wavelengths are longer (or more to the point, at lower frequencies) thedampening property of the vehicle is insignificant [11]. The equation should therefore pro-vide a reasonable estimation of the vibration frequencies where the roughness is of longerwavelength. Vibrations with a frequency of 0.1 Hz are caused by roughness (unevenness)with wavelengths of about 85 m at a travel speed of 30 km/h (8.3 m/s) and wavelengths ofabout 360 m at 130 km/h (36.1 m/s). A vibration frequency of 0.5 Hz is caused by rough-ness with wavelengths of some 15 - 20 m at a speed of 30 km/h and 70 m at 130 km/h. λ = v/fFormula 5 The basic relationship between roughness wavelength, travel speed and vertical vibration frequency (one wheel, no suspension). 28(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E4.5 Transmission of vibrations through the vehicleThe magnitude of the vibration transmitted to vehicle occupants through the vehicle de-pends on the road roughness and the speed of travel, as shown clearly in Figure 7. This isaccentuated by the mechanical properties of the vehicle. For instance, those riding inhigher vehicles are exposed to a greater amount of pitch and roll than those in low vehicles[13].Two-axle cars, are said to have three natural frequencies for vertical vibrations: one that isrelated to the car body bouncing on its suspension, one that is connected to the wheel axlehop between the body suspension and the tyre suspension, and one that originates fromthe rocking of the car seat. The car body has a natural frequency of about 1 Hz, and vibra-tions close to this frequency are amplified by a factor of 1.5 – 3.0. The wheel axles of a carhave a natural frequency of 10 – 15 Hz, which means that at this frequency they tend tovibrate more than what the car body and tyres together with the road surface would di-rectly cause [13][14].Formula 5 indicates that a vibration frequency of 1 Hz when travelling at 90 km/h iscaused by roughness with wavelengths of about 25 metres. Vibration frequencies of 10 –15 Hz at 90 km/h seem to be caused by roughness with wavelengths of about 2 - 3 metres.Multi-axle vehicles that are both heavy and long may have considerably different mechani-cal behaviour than normal cars, particularly if they are towing heavy trailers. Moreover, theproperties of heavy vehicles are changed substantially by the actual weight of the payload.Some types of heavy-duty vehicles lack suspension altogether.The natural frequency of the roll of heavy vehicles is less than 3 Hz. Since roll motions atfrequencies under 5 Hz are not common when driving on roads with ”normal”(?) rough-ness and at normal speeds, it is not usually considered to be of any greater significance.[55]. This item will be under further discussion later in the report.The current European trend towards fewer and more specialised hospitals is resulting in agreater percentage6 of ambulance transports having to cover longer distances while simul-taneously administering intensive care. To manage this, more -- and heavier -- medicalequipment is required on board. Ambulances must then have a greater load capacity thanbefore, which means that large vehicles (”container ambulances”) designed similarly totrucks are needed. See Figure 11. An effective load capacity of more than a tonne is notunusual.In many cases it has been shown how even slight road roughness can, through vibrationand dynamic weight transfer, cause the wheel load to temporarily exceed twice the staticload and then revert just as suddenly to 0 (zero!) during the ride. See Figure 12. A feelingfor how dynamic loads can originate can be created by bouncing a little on the bathroomscales. That the road grip varies between the wheels – and moreover is occasionally non-existent – involves a major risk of skidding when hitting the brakes in an emergency. [3].Dynamic loads have been proven to be a large problem when weighing vehicles in motion,even on very smooth road stretches [48].6Today, there already are some 850 000 ambulance transports per year in Sweden. Of these, about 200 000are emergencies [29, 17]. 29(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Figure 11 Well-equipped “Mobile Intensive Care Unit” type of ambulance. The effective load capacity of the vehicle in the picture is 1.44 tonnes. Notice the heavy- duty wheels, which are even mounted in pairs at the rear. Wheel load Wheel axle hopRoad roughness profile Figure 12 Dynamic change in the wheel load when driving on a rough road [57]. The static wheel load is designated as ”p” in the figure. As seen here, the actual wheel load -- which determines the road grip and thereby the risk of skidding when braking -- varies between 0 (zero!) and twice the static load as roughness in the road profile causes vibrations and weight transfer in the vehicle. 30(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E4.6 Whole-body vibrationDescribing the consequences of shaking the whole human body -- a complex, active, intel-ligent structure -- is not a completely simple matter. The National Board of OccupationalSafety and Health has compiled the known effects of humans being over-exposed towhole-body vibration. A few of the conclusions were: ”It can be assumed without a doubtthat the human being is negatively affected by whole-body vibration, from both a subjec-tive and objective perspective” and ”It would obviously be desirable from everyone’s pointof view if vibrations could be totally eliminated” [51].Needless to say, there are also vibrations that are positive. For instance, vibrations thatinform drivers about the movement of their vehicle, [11, 66], that they are driving over azebra crossing or that the right front wheel ha s a puncture. For safety reasons, such vibra-tions -- ”a sense of the road” -- should not be dampened.Like auditory stimuli, sensory impulses impart strong impressions. These should thereforebe used sparingly, since they partially block or suppress other sources of information. [57].For instance, unlike operators of forestry machinery working out in the woods, those driv-ing on public roads find it completely reasonable to expect the underlying surface to besmooth enough that any vibration generated would be insignificant. In an upcoming ECdirective for limiting exposure to whole-body vibration, it is stipulated that ”the risks aris-ing from exposure to mechanical vibration shall be eliminated at source or reduced to aminimum [with the aim of reducing exposure to below the threshold level].”The survey conducted by the National Board of Occupational Safety and Health on theeffects of overexposure to whole-body vibration showed that although this primarily causesfatigue, it also gives rise to visual acuity disorders, motion sickness, dizziness,back/abdomen/face pain, headaches and a frequent need to urinate [51].That very extreme acceleration causes bodily injury is a factor that has set limits on themanoeuvrability of manned fighter aircraft. Based on fracture mechanics, it is not unlikelythat even the substantially less intensive forces (but at higher frequencies) that cause more”normal” whole-body vibrations can cause physical injury in connection with long-termexposure.When being subjected to vibration, human body reflexes try to protect organs that are sen-sitive to resonance through a tightening of the muscles (this is only successful for veryshort periods - seconds) [38]. Lengthy exposure to vibration therefore often results in highmuscular tonicity [15], which is dangerous to health on many accounts.A governmental working committee on public health has estimated that the cost to societyfor back problems, which is the primary reason for people reporting in sick and for earlydisability retirement in Sweden, exceeds SEK 20 billion per year (1991). In its report, thecommittee also ascertained that whole-body vibrations are of ”key importance” as a sourceof back problems [53]. However, in the general health statistics, the concept of whole-bodyvibration is lacking. ”Vibration injuries” primarily refers to hand/arm vibrations [33]. InEngland a direct relationship has been found between the frequency of back problems andthe distance travelled per year [60]. 31(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EThe findings of a recent review of epidemiologic studies conducted between 1986 and 1997on the relationship between exposure to vibration and problems in the lumbar part of theback provided ”clear evidence for an increased risk for LBP disorders in occupations withexposure to WBV. Biodynamic and physiological experiments have shown that seatedWBV exposure can affect the spine by mechanical overloading and excessive muscularfatigue, supporting the epidemiologic findings of a possible causal role of WBV in the de-velopment of (low) back troubles”. The review also mentions that it is estimated that 4-7%of the working population in the EU is exposed to potentially harmful whole-body vibra-tion [74].Surveys have shown that truck drivers are exposed to considerably greater vibrations thanmost other categories of road user. The exposure often exceeds the recommendations andlimits in the International Vibration Standards [10, 7], as well as the limits proposed by theEU.Sensitivity to vibration differs substantially between men and women. Women (and thefoetus) are particularly sensitive during pregnancy [30].Those who are most sensitive to vibration are injured, sick or disabled people who oftenrequire ambulance transportation. The National Swedish Institute for Working Life hascompared the noise and vibration properties in traditional ambulances and the increasinglymore common larger MICU container ambulances. A major difference was found. The rmsfor vertical vibration (0,5 – 80 Hz) at the driver’s seat in a large ambulance amounted to asmuch as 1.44 m/s2. Interpretations of the findings indicate that levels above 0.5 m/s2 entailan excessive risk for any normally healthy person sitting behind the wheel 6 hours a day.The surveys also showed that the vibrations in an infant incubator on board are often evengreater than at the driver’s seat. On one occasion, the rms for the vertical vibration in theincubator was ranked as a 5 (very uncomfortable) on a six-grade scale of discomfort in theISO 2631-1 “Evaluation of human exposure to whole-body vibration” standard. [17, 29].According to ambulance orderlies, acute motion sickness is a common problem for staffand patients alike.More can be learned about the effects of whole-body vibration in the report by Prof.Ronnie Lundström [65]. Additional information – including the effect of such loads as lowfrequency noise and infrasound – can be found in other reference literature compiled inChapter 8 as well as from such sources as the National Board of Occupational Safety andHealth, the National Swedish Institute for Working Life’s Vibration Committee [31], Upp-sala Academic Hospital [15] and the Swedish Road and Transport Research Institute.4.6.1 Natural frequencies and resonance in the human bodyAll material bodies have a natural frequency, which to some extent can be compared to thenatural frequency of a swinging pendulum. When a body is exposed to a frequency vibra-tion that coincides with its own natural frequency, it will vibrate strongly.The various parts and organs of the human body have different natural frequencies. Thismeans that the body does not vibrate uniformly, but rather that the different parts behavelike individual, albeit interlinked, material bodies in this respect. (See Figure 2). Externalvibrations with frequencies of about 6 Hz are amplified through resonance in the abdomenby up to 200%. Certain vibrations are amplified in the spine by up to 240%. The head has a 32(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31Enatural frequency of about 25 Hz, which means that vibrations with frequencies aroundthis are amplified by up to 350% [41][42]. The resonance phenomenon leads to a greaterload on the body and thereby a greater risk of injury.4.6.2 Examples of the effect of whole-body vibration in the 0.5-80 Hz rangeShortwave road roughness produces vibrations with a frequency content that among otherthings includes the 0.5 - 80 Hz band.According to the ISO 2631-1 standard, vibrations with frequencies between 0.5 - 80 Hzcould probably cause a greater risk of injury to the vertebrae in the lumbar region and thenerves connected to these segments. Exaggerated mechanical strain can be a factor in thedeterioration of the lumbar segments. Vibrations are reported as affecting the bodythrough causing deformation of the spine (spondylosis deformans), damaging the cartilagebetween the vertebrae (osteochondrosis intervertebralis), and by producing chronic pro-gressive change in the cartilage and bone tissue (arthrosis deformans). Exposure to whole-body vibration can also exacerbate certain endogenous pathological disorders of the spine.It is not considered unlikely that the digestive system, the urinary and sexual organs and thefemale reproductive organs are affected. Health impairment caused by whole-body vibra-tion normally only occurs after several years of exposure [10]. Spontaneous abortion is anexception.4.6.3 Examples of the effect of extremely low frequency whole-body vibrationsLongwave road roughness produces low frequency vibrations. Vibrations with greater am-plitudes within the 0.1 – 0.63 Hz frequency band have a particularly strong effect on peo-ple.According to the ISO 2631-3 standard, these vibrations cause various degrees of motionsickness, ”travel sickness”, even after only short exposure. Motion sickness can affect peo-ple for hours, and even up to days after an arduous trip. It has been observed that motionsickness lowers performance ability and reduces alertness.A survey conducted amongst 300 students revealed that about 58% had felt nauseous dur-ing car rides. Some 33% could remember actually having vomited during car trips beforethe age of 12 [11].A nationwide questionnaire revealed that motion sickness is a frequent working environ-ment problem amongst ambulance orderlies. 23% replied that they easily felt nauseousduring the ride. [27]. Orderlies in Sollefteå Municipality reported having observed palpabletravel sickness symptoms in patients (in the worst case vomiting, uncontrollable bowelmovements, etc) in 20-25% of the most acute (high speed) transport situations. In the careunit of the vehicle, it is impossible to watch the horizon.Vehicle manufacturers are aware that the suspension properties affect the risk of passen-gers developing motion sickness. A sports car type of suspension is recommended forpeople who easily get car sick. It cannot be ruled out that ”comfort suspension” -- byAmerican standards -- can mean that the high frequency vibrations caused by road surfacedamage are converted to an exceptionally high degree into that very type of low frequencyvertical vibration that is known to cause motion sickness. It is also known that rotationvibrations are a factor in motion sickness. Perhaps even the differences in roll-stability be- 33(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31Etween different vehicles has a major impact? Added to the ”motion sickness vibrations”created by the ride are the low frequency vibrations that ensue from the billowing align-ment that roads originally built for horse drawn carriages often have.4.6.4 Origin of whole-body vibrationAccording to the Academy of Engineering Sciences (IVA) road roughness is a muchgreater cause of vibration in road vehicles than in-vehicle factors (wheel imbalance, drive-line, etc.). IVA has also ascertained that vibrations have a major impact on the steering andbraking properties of the vehicle, and on the working environment, ride quality, health andpossibly even performance ability of vehicle occupants [19].Whole-body vibrations originate from two different types of force. A random and suddenforce designated as shock. When the wheel hits a bump or sinks into a pothole, shock oc-curs. If this shock is strong enough, passengers without a safety belt can be thrown fromtheir seat. They could also be hit by a loose-flying object. Shock can also cause severe spi-nal injury [32], such as in several Scandinavian cases due to riding in buses over trafficcalming road humps. Less sudden displacements and forces occur during a normal ride onmore or less rough roads. See Figure 13 - Figure 15. These are the most common motioninduced forces that we experience during a normal day [42]. The second law of Newtoncan be used to calculate the dynamic forces that vibrations transfer to human organs.Certain types of vibration are known to cause car sickness. These include extremely lowfrequency vertical vibrations (0.1 – 0.63 Hz) and roll (often in combination with lateraldisplacement). The low frequency vertical vibrations are caused by exceedingly longwaveroughness (up to 350 m), but can also occur when a vehicle with worn or poorly designedwheel suspension transforms high frequency vibrations to low frequencies. Roll occurswhen there is an unfavourable variation in the gradient between the wheel tracks (crossfall);this often is caused by roadway deformations and all too sharp curves in the alignment.The limits for whole-body vibration in the ISO 2631-3 Standard can be converted intostandard specifications for the road roughness profile. See Figure 16. On roads where thereis substantial roll (caused for example by sharp curves or deformed edges) the acceptablelongwave road roughness must be reduced by 25%. Major vertical motionFigure 13 Origin of vertical vibrations on roads where the roughness wavelength coincides with the distance between the vehicle axles. Adapted from [66] 34(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EMajor pitch and thus major longitudinal vibration Little vertical movement Figure 14 Vibrations in the direction of travel occur when the wavelength of the road roughness does not coincide with the distance between the vehicle axles. Adapted from [66]. Major roll and thus substantial lateral vibration Figure 15 Origin of lateral vibrations on a road with deformed edges 35(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E 2.00 1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00 153 122 95 76 61 49 38 31 24 Length of the hollow or ridge (i.e., half the roughness wavelength), [m]Figure 16 Limits for longwave roughness at a speed of 110 km/h, set with respect to the criterion for decreased performance ability. The values are derived from the vibration limits in the ISO 2631-3 standard. The corresponding limits with respect to the discomfort criterion are considerably stricter. The limits assume no surface defects at all (aggregate stripping, potholes, etc) or damage that cause rota- tion vibration (unevenness at culverts, edge deformation, etc).4.6.5 Measurement of whole-body vibrationThe measurement of whole-body vibration must comply with ISO 2631 “Evaluation ofhuman exposure to whole-body vibration” (1997). The equipment consists of accelerationsensors, arranged as shown in Figure 17 and Figure 18.The reaction time for the sense of motion has been found to be 0.24 – 0.80 s, with a meanvalue of 0.72 seconds [57]. This is one of the reasons why comfort-related measurementsare normally done through integration over 1-second intervals. A vehicle travels 20 m in asecond, at the speed of 72 km/h. This means that vibration data measured in compliancewith ISO 2631 at rural highway speeds on sub-stretches are fairly comparable in length toroad roughness data in the SNRA road surface condition database, which after sampling atthe mm-level was ultimately averaged over 20 m intervals. 36(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 17 Vibration measurement gauge on the seatFigure 18 Vibration measurement gauge on the floor 37(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E5 MethodField surveys were conducted between the 27´th and 29´th of October 1999. This late datein the season meant risking wintry road conditions, which also proved to be the case on themorning of the 28´th. The light snowfall during the night meant that the highest frequencyvibrations caused by the roadway texture were somewhat lower. As these are not particu-larly high energy, this situation was not considered to have affected the study in a way thatwould result in any greater underestimation of the vibration problem.5.1 Test stretches 1 2Figure 19 Location of the roads surveyed. Sollefteå Municipality, Väste rnorrland County. The stretch on National Highway 90 is indicated as 1, and that on County Road 950 as National Highway No. 90The stretch of highway surveyed is located north-west of Sollefteå, between Näsåker andRemsle, see Figure 19. The survey was conducted in an easterly direction. The roughnessmeasurements heading towards Sollefteå began (not counting an approach of a little over300 m) at the intersection by Flintabaren in Näsåker. The IRI20 values on 32 kilometres of 38(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31Ethe rough roadway (!) were very high, up to 14.90 mm/m. The alignment was very poor inplaces, and the accident rate high, particularly in winter.It was estimated that a budget of SEK 2500/m would be needed for proper remedial ac-tion on the rough part of the stretch. This amounts to a total of SEK 80 million for the 32kilometres in question.At Skarped, the road abruptly becomes relatively smooth for some 5 kilometres (IRI20 val-ues drop all the way down to 0.43 mm/m, despite occasional bumps where the IRI20 valuesare between 2 – 5 mm/m). This is due to an up-grading project in 1995 (reconstruction,frost protection in places and alignment improvements). The smooth stretch ends a joint inthe road surface just west of Santa’s Village at Remsle, Sollefteå. This stretch can serve asan example of how good a road in Västernorrland County can be a few years after remedialaction, if reasonable funding is allocated. A stretch of about 2 kilometres was surveyed inthe town as well, but was not analysed. The measurements ended at the intersection by theShell petrol station at Remsle, Sollefteå.5.1.2 County Road 950The stretch covered some 21 kilometres of road west of Långsele (Sollefteå Municipality),on the south side of the Faxälven River, running in an easterly direction between Helgumand Holmsta. The roughness measurements started (not counting an approach of a littleover 300 m) at the intersection with the road from the bridge across the river at Holmsta,and ended at the intersection with Road 331 at Helgum. The survey was limited to measur-ing vibrations in a Mercedes ambulance at a relatively low speed, and in an unloaded truck(Scania) pulling an empty trailer at very low speed.The alignment is poor in spots, and the road is generally in a deplorable shape, with IRI20values up to 22.89 mm/m in the summer. During the spring thaw, parts of the road arealmost completely impassable, and have been included in a feasibility study within theframework of the multi-year “BÄRUND” bearing capacity project carried out at the Cen-tral Region of the Swedish National Road Administration. This means that an excellenttechnical study has been conducted involving falling weight deflectometer tests, a groundpenetrating radar survey, sampling and analysis of materials, special surveys under frozenground conditions using a laser profilometer adapted by VTI for research purposes. (Dur-ing this survey the highest IRI20 value measured was 42.14 mm/m. Further, it took twodays to repair the damage to the vehicle after its having been used in the survey).The results from the measurements conducted through the BÄRUND project have beenused for the design analysis for both frost-proofing and reconstruction needs. This guara n-tees a good basis for calculating the price for remedial maintenance and sustainableimprovement works. It has been calculated that a budget of some SEK 1400/m is required,which amounts to SEK 29.4 million for 21 kilometres. The cost (consumption of resourcesduring the period of use) for the works depends on the life span of the road. Insufficientmeasures are extremely costly. 39(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E5.2 Vehicles5.2.1 AmbulancesTwo different ambulances with stretchers were provided by the ambulance medical servicesin Sollefteå Municipality. One was a 1991 Chevrolet 3500 (see Figure 20 & Figure 21), de-signed and equipped for transport, intensive care treatment and for monitoring patients.The car complied with the requirements for ”Mobile Intensive Care Unit” in the Europeanstandard for ambulances, EN 1789, and had a effective load capacity of 1.44 tonnes. Thewheel suspension had recently been completely renovated.Figure 20 Chevrolet 3500 MICU ambulanceFigure 21 Vibration gauge on the stretcher in the ambulance 40(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EThe other car was a 1991 stretch (60 cm) Mercedes 280, designed and equipped for trans-port, minor treatments and monitoring of patients. It complied with the European standard”Emergency ambulance”.The ambulances were driven both at a ”low speed” and a ”high speed”. On NationalHighway 90, low speed meant setting the cruise control at 90 km/h. High speed entailedthe driver trying to maintain a speed of 140 km/h, meaning that the speed varied between110 - 140 km/h with a mean speed of about 120 km/h. On County Road 950 it was onlythe Mercedes that was tested, at a speed of about 70 - 90 km/h. ”The patient” weighedabout 80 kilos.5.2.2 Heavy trucksSCA Forest And Timber AB and Själanders Åkeri AB hauliers provided two heavy trucksand attached heavy trailers, equipped for transporting timber. One of them (model year1991) had gone some 960 000 kilometres and was quite run down. The seats were theoriginal ones and the driver’s seat had air suspension. The other truck (model year 1999),see Figure 22, had gone some 96 000 kilometres and was like new to all intents and pur-poses. The driver’s seat had been replaced by a special seat with air suspension and pull-push isolator to reduce horizontal vibration. The passenger seat was the original. Technicalspecifications for both vehicles is given in Table 1. The driver weighed about 90 kilos.The trucks were driven at a speed that complied with normal schedules. Through compar-ing the tachograph reading with the total time it took to drive the test stretches, this meantsome 75 km/h on Highway 90, with a somewhat higher speed when the trailer was unloa-ded, and somewhat lower when it was. The driver did not dare keep the speed that normalschedules would demand on County Road 950 for fear of sudden vehicle damage or anaccident. As a result, the vehicle drove at about 55 km/h when the trailer was unloaded,with variations between 40 and 60 km/h except on certain occasions when the speed wasreduced to about 5 km/h. In places where the roughness was extreme, it actually happenedthat the driver felt forced to drive on the wrong side of the road (!), which caused ”errors”when collating this with the SNRA’s road condition measurement data.Figure 22 Heavy truck with a heavy trailer 41(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EType of vehicle Heavy lorry Type of vehicle Heavy lorryMake Volvo Make ScaniaModel F12 6x2 Model 144GModel year 1990 Model year 1999Miscellaneous Load exchanger Miscellaneous JOAB Kameleont type of superstructure enabling easy change between a timber frame, tip platform, trailer turntable, etcNumber plate OUC 045 Number plate GUW 055Odometer about 960 000 km Odometer about 96 000 kmDrivers seat Air suspension Isri (standard) Drivers seat Air suspension, isolator Isringhausen Medium BPassenger seat Passenger seatFront tyres Front tyresMake Bridgestone Make MichelinType M758 Type X XZYDimension 385/80 R 22.5 Dimensions 385/65 R 22.5 2 2Pressure 8 kg/cm Pressure 8 kg/cmRear tyres, shaft Rear tyres, shaftMake Michelin Make MichelinType X XDN Type X XDNDimensions 12 R 22,5 Dimensions 12 R 22,5Assembly Pair Assembly Pair 2 2Pressure 6.5 kg/cm Pressure 6.5 kg/cmRear tyres, pulley axle Rear tyres, pulley axleMake Continental Make MichelinType Type X XDNDimensions 11.00 x 20 Dimensions 12 R 22,5Assembly Pair Assembly Pair 2 2Pressure 6.5 kg/cm Pressure 6.5 kg/cmTrailer TrailerMake Kilafors MakeType Timber trailer Type Timber trailerRegistration no. Registration no.Axle configuration 2 axles both front and back Axle configuration 2 axles both front and backTyres, make Bridgestone Tyres, make Michelin X XTYDimensions 275 70 225 Dimensions 265/70 R 19,5Assembly Pair Assembly Pair 2 2Pressure 7.5 kg/cm Pressure 7.5 kg/cmTable 1 Technical data for the trucks 42(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E5.2.2.1 Load variationsThe following types of load were tested on National Highway 90: LB type 1, unloaded without trailer LB type 1, loaded without trailer LBs type 1, unloaded truck unloaded trailer LBs type 1, loaded truck loaded trailer LB type 2, unloaded without trailer LBs type 2, unloaded truck unloaded trailerOn County Road 950, it was only LBs type 1 that was tested, unloaded with an unloadedtrailer. The speed on that occasion was also considerably lower than on National Highway90. See section 5.2.2 43(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E5.3 Measurement and analysis of whole-body vibrationsThe measurements and analysis were conducted by Kjell Ahlin, Licentiate in Engineeringof Ingemansson Technology AB and are detailed in a report [64]. The analysis in principleis shown in Figure 23 and Figure Variables • Vertical and horizontal whole-body vibration, and both roll and yaw rotations ob- tained through synchronised measurement on the floor and at the driver and pas- senger seats. Frequency range 0.5 - 80 Hz in compliance with ISO 2631-1 (revised 1997). • Vertical measurements at a frequency range of 0.1 - 0.63 Hz in compliance with ISO 2631-3 (1985).The plans contained two methods (redundancy) for registering real travel speed and currentposition along the road to enable collation with existing road surface condition data. Oneinvolved a mounted measuring wheel with a pulse transducer, and the other GPS. Ar-rangements had been made to borrow the measuring wheel from the Swedish ArmedForces. Unfortunately, it arrived too late and could not be used. The GPS receiver brokedue to severe shocks during the first run. A video film was taped simultaneously. This film,with its time indicator, was later used as an aid during the data collation.Figure 23 Flow chart for measurement and analysis of whole-body vibrations 44(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 24 Calculating the quality of the ride in relation to the vibration at the different points of measurement and as an overall impression. 45(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E5.4 Expert analysis of the effect of vibration on the human bodyAn expert analysis of the effect on the human body of the vibrations measured was con-ducted at the National Institute for Working Life. The findings are presented in a separatereport [65]. See also chapter 7.5.5 Collation between the vibration data and the data from the road condition surveysThe aim was to develop a correlation model for the translation vibrations as a function ofIRI, based on values measured on National Highway 90.Since the real speed varied somewhat during the runs, the analysis was initiated by dis-criminating individual measurement values (both IRI values and vibration values) to keepthe distance synchronisation of the measurement series from ”getting out of hand”. Theanalysis was then based on the mean values on 100 m long stretches. After having studieddescriptive statistics for data in a computer environment (histogram, distribution, etc.), itwas found suitable to classify the material according to IRI100 values. Classes 0 < IRI100 < 3mm/m, 3 < IRI100 < 5 mm/m, and IRI100 > 5 mm/m were chosen for the Mercedes ambu-lance driving at low speed. In all the other cases, classes 0 < IRI100 < 3 mm/m and IRI100 >3 mm/m were chosen. This was followed by a regression analysis, whereby a linear regres-sion model was found to give the best results. The results are presented in Chapter Effect of emergency action, ”the devil’s choice”, on National Highway 90The road condition data that was collated with the vibration data was collected during thesummer of 1999. In the autumn of 1999 spot emergency actions was taken to reduceroughness on the stretch at hand. See Figure 25. This meant correcting steep deformations(amplitude ca 50 – 300 mm) with crushed gravel, which was then provisionally coveredwith a bitumen mix. 46(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 25 Emergency repair on National Highway 90 between Skarped and NäsåkerVehicular roll motions drastically reduces where spot actions had been taken, particularlywhen the repair was close to the edge of the road. This also facilitates effective road main-tenance during the winter ahead, of course very positive with a view to road safety. How-ever, spot repair often means a heterogeneous road texture, which leads to split frictionbetween the wheels, especially when the moisture on the road begins to freeze. In connec-tion with moisture/freezing, even colour differences are a significant factor, as this affectsthe absorption of solar heat.Split friction considerably increases the risk of skidding. For cars, there is a greater risk ofskidding when braking sharply on bare roads than on winter roads. This is due to fact thatthe load on the rear axle is lightened through vehicle pitch in the first case, reducing theroad grip of the rear wheels. On the other hand, steering control is lost faster on winterroad surfaces than on bare roads. It becomes difficult to avoid rear wheel skid in situationswhere the rear wheels have less road grip than the front wheels when braking [3].Hence, split friction means a much greater risk of skidding when having to brake sharply,or it can cause the ”jack-knife” phenomenon for a truck with a semi-trailer, making it im-possible for the driver to maintain control of the vehicle. For this reason, spot repairsshould be done so that the texture is the same as on the surrounding surface. It is advisablethat the repair cover the entire lane width. There is always somewhat of a height discrep-ancy on the road surface at all temporary patching. This can significantly reduce the dy-namic contact between the tyres and the roadway, which is an obvious safety hazard.Action similar to that shown in Figure 25 can be described as the ”devil’s choice”, the leastbad alternative where maintenance budgets are all too constricted. 47(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31ESince the remedial action had not affected the condition of the road surface other than inspecific spots, it was concluded through consultation with the regional road authority thatthe conclusions from vibration study would not be affected enough to warrant an addi-tional road condition survey in the autumn of 1999. The vibration measurements were thencarried out after the emergency repair. At that point it was found that the repairs had al-ready disintegrated after only two months. 48(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E6 ResultsWhen first driving in a large, comfortable 1999 car model on the ”rough” test stretch ofHighway 90, those taking part in the vibration survey wondered why the Swedish NationalRoad Administration had not chosen a road in poorer condition. During the subsequentruns inside the trucks, the same people commented that ”this is not much different thandriving through the forest in an army tank”.During the survey, they occasionally found it hard to speak because of the vibrations.While riding in the care unit of the ambulance, members of both the survey team and the”patient” experienced clear signs of motion sickness -- perspiration, pallor, nausea and diz-ziness -- when there was little opportunity to keep their eyes on the horizon. Before start-ing, and at the end of each run, they had to get out of the ambulance for some fresh air.They also found eating difficult on their lunch break.Both road authority employees and the survey team had back pain for about ten days afterthe intensive round of test driving.A full account of the measurements and analysis results is contained in a separate report[64].The expert analysis of the impact of the vibrations on the human body, conducted at theNational Institute for Working Life, is presented in a separate report [65]. A summary ofthe conclusions is compiled here in Chapter 7.The following are extracts from the SNRA’s current data on the road surface condition andthe results from collating this data with the vibrations measured inside vehicles. 49(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E6.1 Road surface condition as per the SNRA’s ”PMS” database6.1.1 Roughness expressed as International Roughness Index Rv 90: Fördelning av mätsträckornas ojämnheter (IRI-värde) 60 50 Jämn: Skarped - Remsle Ojämn: Näsåker - Skarped 40 Antal observationer 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 IRI-värde [mm/m]Figure 26 National Highway 90: IRI20 distribution. Values from the smooth stretch in blue, values from the rough stretch in pink. Mätsträckor på Rv 90 Sträckornas ojämnhet uttryckt i måttet IRI [mm/m] 8,00 7,00 6,00 5,00 Medelvärde IRI Stdavv IRI 4,00 5 percentil IRI 95 percentil IRI 3,00 2,00 1,00 0,00 Jämn: Skarped - Remsle Ojämn: Näsåker - SkarpedFigure 27 National Highway 90: statistical properties of the distribution of the IRI20 values. Smooth stretch to the left, rough to the right. 50(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Rv 90, jämn del 15 10 Ojämnhet IRI 5 0 67000 67397 67797 68197 68597 68997 69397 69797 70197 70597 70997 71397 SektionFigure 28 IRI20 values, extract from the smooth stretch of National Highway 90. Even here there are a couple of substretches that clearly have a sharp effect on vehi- cle motion and ride quality. Rv 90, ojämn del 15 10 Ojämnhet IRI [mm/m] 5 0 92003 92403 92803 93203 93763 94163 94563 94963 95363 95763 96163 96563 96963 Sektion [m]Figure 29 IRI20 values, extract from the rough stretch of National Highway 90. Where the IRI values are as high as they are here, one must drive extremely slowly to avoid uncomfortable vibrations. However, commercial drivers especially must keep to a time schedule, which often dictates the speed, and the only variable is the cab vibration. 51(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E6.1.2 Crossfall Rv 90 10 8 6 4 2Tvärfall 0 0 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 00 41 69 83 11 13 27 55 97 25 39 53 67 81 95 09 23 37 51 65 79 93 07 21 35 49 63 77 91 05 19 33 47 61 67 67 67 67 68 67 67 67 67 68 68 68 68 68 68 69 69 69 69 69 69 69 70 70 70 70 70 70 70 71 71 71 71 71 -2 -4 -6 -8 -10 SektionFigure 30 Crossfall, extract from the smooth stretch of National Highway 90. The red lines show maximum permissible crossfall [%] in curves when constructing a new road (target value, excluding tolerance margins). Rv 90 10 8 6 4 2 Tvärfall 0 82791 83191 83591 83991 84391 84791 85191 85591 85991 86391 86791 87191 87591 -2 -4 -6 -8 -10 SektionFigure 31 Crossfall, extract from the rough stretch of National Highway 90. The red lines show maximum permissible crossfall [%] in curves when constructing a new road. Notice the substantial, abrupt changes in the crossfall, which causes ma- jor roll motions when driving at a normal travel speed. 52(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E6.1.3 Lane cross-sections Rv 90: tvärsektion bildad över 20 m i östgående körfält Delsträcka med jämn vägbana och där låga vibrationsnivåer uppmätts 35 25 15 5 Nivå [mm] 0 500 1000 1500 2000 2500 3000 -5 -15 -25 -35 Sidoläge (mm)Figure 32 Lane cross-section, smooth stretch of National Highway 90. Exaggerated vertical scale. Rv 90: tvärsektioner bildade över 20 m i östgående körfält Delsträcka med ojämn vägbana och där mycket höga vibrationsnivåer uppmätts 35 25 15 5 Nivå [mm] 0 500 1000 1500 2000 2500 3000 -5 -15 -25 -35 Sidoläge (mm)Figure 33 Lane cross-sections, rough stretch of National Highway 90. Exaggerated vertical scale. 53(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E6.1.4 Seasonal variation in road roughness, County Road 950Figure 34 shows that there can be a vast difference in roughness between winter and sum-mer. VTI conducted the winter survey within the framework of the SNRA Central Re-gion’s BÄRUND project (bearing capacity survey). Ojämnheter (20 m), Y 950 14 12 Den tjälrelaterade ojämnhets- ökningen är här ca 450 % 10 IRI IRI sommar 96 [m m/ 8 IRI vinter 98 m] RUD, åtgärd 20 m RUD, åtgärd 400 m 6 Mål e. rekonstr. 4 2 0 28 68 108 148 188 228 268 308 348 388 428 468 508 548 588 628 668 706 756 796 836 876 916 956 996 1036 Sektion [m]Figure 34 Variation in road roughness IRI between summer and winter. The summer survey is shown by the dark green dotted line, and the winter survey by the blue dotted line. The horizontal green line shows the target level after reconstruc- tion, the red and orange lines show the SNRA’s recommended specifications for maintenance and operations (RUD) [24 ]. Seasonal differences up to 450% can be seen. 54(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E6.2 Cab acceleration model as a function of road roughness (IRI)Figure 35 shows a typical example of a derived model for the relation between truck cabvertical vibration acceleration (that is frequency weighted etc as specified in ISO 2631-1),and road roughness measured as IRI value.There is a greater variance in cab vibration acceleration at road roughness levels above 3mm/m. This is probably due to the fact that the IRI is attuned to reflect the resonancefrequencies of cars rather than trucks and that the acceleration of the vibration in the cab,unlike the IRI, is frequency weighted (see Figure 39). It could also be due to the emergencyroad repair undertaken in the period between the road roughness survey and the cab vibra-tion survey and to the fact that vehicles changed their lateral position on the carriageway toavoid major visible roughness (even to the extent of driving on the wrong side of the road).Even a ny minor changes in speed would have some effect. Truck with trailer (75 km/h) 2,0 1,6 Dz [m/s ] 2 1,2 0,8 Measured 0,4 Regression Fit 0,0 0 1 2 3 4 5 6 7 8 9 10 IRI [mm/m]Figure 35 Regression analysis (prior to the division into IRI classes) for vertical translational vibrations at the seat in the truckFigure 36 presents the resulting relationships, which can be used to calculate the meanvalue over 3 – 5 seconds of the (x, y, z)-vector translational vibrations with a frequency of0.5 – 80 Hz in the cab (at the truck driver’s seat and on the stretcher in the ambulance),given that one knows the IRI100-values. 55(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Trucks and ambulances Model for predicting translational vibrations from International Roughness Index 2.5 2.0 1.5 1.0 0.5 0.0 0 1 2 3 4 5 6 7 8 IRI [mm/m], average during 100m MICU ambulance, 120 km/h Emergency ambulance, 90 km/h New Truck + Trailer, unloaded, 75 km/h Old Truck + Trailer, unloaded, 75 km/h "The Golden Car" (only z-direction) A little uncomfortable Fairly uncomfortable Uncomfortable Very uncomfortable Extremely uncomfortableFigure 36 Model for (x, y, z)-vector translational vibrations as a function of road roughnessFormulae 6 and 7 can be used to mathematically describe a model for translational (x, y, z)-vector vibrations in trucks (with a trailer) in normal condition and travelling at a speedaround 75 km/h. A similar relationship for a large ambulance travelling at a speed of about120 km/h can be described by Formulae 8 and 9. The best degree of correlation is ob-tained through using Formulae 6 and 8. Formula 10 is used to calculate the sensitivity ofthe IRI model, restricted to vertical (z) motion only.RMS ( atranslation ) = 0.18 + 0.30 * IRI 100Formula 6 Translational vibrations in a truck with a trailer at an IRI100 of 0 – 3 mm/mRMS ( atranslation ) = 0.35 + 0.22 * IRI 100Formula 7 Translational vibrations in a truck with a trailer at an IRI100 of > 3 mm/mRMS ( atranslation ) = 0.04 + 0.33 * IRI 100Formula 8 Translational vibrations in a large ambulance at an IRI100 of 0 – 3 mm/m 56(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31ERMS ( atranslation ) = 0.49 + 0.20 * IRI 100Formula 9 Translational vibrations in a large ambulance at an v of > 3 mm/mRMS ( a z ) = 0.16 * IRI 1secFormula 10 Vertical vibrations in the ”Golden Car” at a speed of 80 km/h 57(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E7 DiscussionAn expert analysis of the effect of exposure to whole-body vibration was conducted byProfessor Ronnie Lundström of the National Institute for Working Life. The following isan account of the discussion in the analysis:”The findings from this pre-study clearly show that drivers and passengers/patientstravelling in logging trucks/ambulances on the rough stretches of National High-way 90 were exposed to an unacceptably high vibration load in connection withseveral of the driving conditions measured. In many cases, the loads reached levelsthat bring a potential or probable health hazard, judging from the guidelines speci-fied in ISO standard 2631-1. The vibration registrations also showed the frequentoccurrence of shock and rotational vibration, both in the vertical and horizontaldirection during the ride. The development of vibration-related injury symptomsamongst logging truck drivers, such as lumbago and ischias, must therefore be re-garded as highly probable under these driving conditions, particularly through re-peated exposure day after day, year after year. Shock, roll and pitch can also resultin body motion that can impair driving performance and consequently the ability ofthe driver to maintain full control of the vehicle. This in turn can jeopardise roadsafety. The analysis of the vibration load in ambulances shows that the ride on therough stretch of National Highway 90 entails a potential, and in some cases even aprobable health hazard based on ISO 2631-1. This interpretation applies to healthyindividuals. It is unclear how this load should be related to the effect on patients inneed of medical care. There are good grounds to assume that they are more vulner-able than healthy people. In any event, the vibration load could cause them addi-tional harm.”A summary of Professor Lundström’s conclusions is contained in section 7.4.1. A completeaccount of the analysis is given in a separate report [65]. 58(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E7.1 Road stretches where the roughness presents a health hazardTo set a limit for an acceptable level of road roughness is not a trivial matter. It is knownthat people are more disturbed when exposed to high levels of several stress factors incombination (e.g. vibration, noise and infrasound) than to one at a time. In other words, acombination of disturbances has an amplifying effect. This cannot be disregarded, as apartfrom causing vibrations, road roughness is a primary source of high frequency sound (>500 Hz), low frequency noise (20 – 500 Hz) and infrasound (< 20 Hz) [72].Let’s take a closer look at a specific example: When heavy vehicles drove over a sharp edgein the road surface that was 25 mm high, the noise level registered at the side of the road 7metres away increased by as much as 23 dB(A). The same study showed that driving in ahollow with an amplitude of 40 mm over a wavelength of 2.4 m resulted in an increase inthe noise level with as much as 29 dB(A), with peak values for total noise up to 106 dB(A).The main source of noise did not come from the contact between tyre and carriageway,which has been the focus of research up until now. It was a much more mundane problem:rattling vehicle parts [4]. Unfortunately, the study did not mention the increase in noiseinside the cab.In the general assessment amongst road authority representatives concerning what levels ofroughness are acceptable, the major focus up until now has been on how they themselvesexperience road stretches with varying degrees of roughness. This approach is, however,highly questionable, since healthy men under short exposure in relatively new comfortablecar models (a category in which almost all Swedish road authority employees on businesstrips can be placed) ought to belong to the least sensitive group of road user. Focus shouldinstead be on road users who are more vulnerable than the average, and on exposure thatapplies to commercial drivers over an extended period of time.One conclusion that can be drawn from the differences shown in the graphs in Figure 36 isthat the effect of road roughness on the vibration level in the cab is about 2 - 3 timeshigher in a truck than in a normal car.An important fact to keep in mind is that the phenomenon of resonance means that tworoads with the same IRI value, but different wavelengths, cause entirely different distur-bances at speeds other than the reference speed of 80 km/h. In practice, this is of key im-portance as illustrated by the following examples:1. Figure 37 shows that the IRI value, which is calculated at a reference speed of 80 km/h, is more than twice as sensitive to roughness with a wavelength of 2 m than when the wavelength is 1 metre. In Figure 38 we can see that if we let the “Golden Car” (the car model used to calculate the IRI value) simulate a ride at a speed of 40 km/h, roughness with a wavelength of 1 m causes acceleration of the cab that is more than twice as high as the resulting acceleration when the wavelength is 2 metres. In practise, this means that it is relatively senseless to evaluate road roughness driving one’s own car at a low speed along the road in question, and expect to achieve an a s- sessment in tune with the IRI values measured by the roughness profilometer vehicles.2. Consider a carriageway that is completely smooth, except for one irregularity where the wavelength is 2 m and the amplitude 10 mm. Figure 38 shows a momentary vertical cab acceleration of 10*0.23/0.5 = 4.6 m/s2 at the reference speed of 80 km/h. If the speed is reduced to 50 km/h the vibration is reduced to 10*0.13/0.5 = 2.6 m/s2. If the speed 59(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E is increased to 120 km/h the vibration is reduced to 10*0.13/0.5 = 2.6 m/s2. (This also means that reducing the speed is not an obvious solution to the problem of vibration. On the contrary, it can intensify the problem (depending on the wavelength of the road damage). See also Figure 7).The phenomenon of resonance also means that the kind of basic relationship that is plot-ted in Figure 37 cannot completely explain the significance of road roughness on cab accel-eration. In order to develop models that can explain this well, the wavelength componentof the roughness must also be taken into consideration. Furthermore, since discomfort hasbeen found to be best correlated with running rms of weighted cab acceleration, integratedover 1 second (and while many roughness elements will typically be traversed at highwayspeed during such a long time frame), it seems unavoidable that ride quality should be a s-sessed from continuous ride simulations rather than from some kind of general relationbetween single roughness components (or compound indices such as IRI-values) and cabaccelerations.Figure 37 IRI value for roughness with an amplitude of 0.5 mm, as a function of wavelength. Source: Study in progress at the SNRA involving a general review of cause and effect. 60(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 38 Floor vibration in the ”Golden Car” for roughness with an amplitude of 0.5 mm, as a function of wavelength. Source: Study in progress at the SNRA involving a general review of cause and effect.As seen in Figure 37, the measurements in the study at hand show that it is uncomfortableto drive an older truck at a speed of 75 km/h on roads where the roughness is calculated atan IRI = 1.8 mm/m. In a new truck, the corresponding figure is 2.3 mm/m. In a large am-bulance at a speed of 120 km/h, an IRI = 2.2 mm/m is uncomfortable for a healthy per-son. In a ”small” ambulance at 90 km/h this is 4.8 mm/m. The mechanical properties inthe smaller ambulance seem to be comparable to a typical passenger car, like the ”GoldenCar” used to calculate the IRI value.Figure 39 clearly shows how vibrations are a function of wavelength and vehicle speed. Thevertical translational acceleration in the figure has been frequency weighted using the ISOfilter (Wk), which takes into consideration human body sensitivity to vibration energy im-mission as a function of vibration frequency. An indication that the IRI value underesti-mates the impact on the human body of road roughness is given when the ratio in the fi g-ure differs from 0.16 (the ratio between the frequency weighted acceleration of the cabacceleration and the IRI value at 80 km/h). It can be observed that the IRI ”gives too lowan estimation” in three areas:• wavelength 1 - 2 metres, speed 30 - 50 km/h;• wavelength 3 - 6 metres, speed 100 - 140 km/h;• wavelength > 20 metres, speed >100 km/hThe implication of this is that a better indicator should be developed and implementedwithin road maintenance. 61(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EIRI values are not enough to indicate the risk of motion sickness and as such should not beused for this purpose. Rather, this risk should be assessed through direct vibration meas-urements, 0.1 – 0.5 Hz, or through studying undulations measured on the carriageway.IRI is, however, preferable to indicators that have been frequency weighted according tothe ISO 2631 standard for human exposure to vibrations when assessing the risk of vehicledamage, dynamic pavement load etc. But also for this kind of assessments, other indicatorsmay be even better than IRI.In light of the above, it is recommended that roughness above the level of IRI20 = 3mm/m should, in practice, be regarded as entirely unacceptable in road maintenance man-agement in Sweden. In other words 3 mm/m in average over 20 meter (corresponding toan accumulated vertical suspension displacement of 6.0 cm during each second of a drive at72 km/h or 20 m/s highway speed) should be seen as a provisional disgrace limit. Beyondthis, an eventual reduction of this limit should be discussed -- and first and foremost --supplementary indicators of disturbances related to vibration be implemented. At present, alower IRI disgrace limit is not, however, of interest, since it is seen in Figure 40 that a limitof IRI20 = 3 mm/m means that the condition on about 1/3 of the state roads is unaccept-able. Considering the budget-/financing need, this presents such a crisis that it is of littleinterest to discuss the grey zone below an IRI20 = 3 mm/m within the foreseeable future.Figure 39 Relationship between the frequency weighted vertical cab acceleration and IRI in the ”Golden Car”. Source: Study in progress at the SNRA involving a general review of cause and effect.Assuming that the initial defects after surfacing works can be kept below IRI20 = 0.6mm/m, once the contractors have learned how to make best use of modern road mainte-nance engineering methods [63], and that the average increase in roughness is 0.1 62(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31Emm/m*years during the life span of the road, this would result in a 24-year theoretical cy-cle of roughness repair actions. A reasonable target would then be that no more than 1/24= 4% would have an IRI20 greater than 2.9 mm/m (the 3.0 limit minus the previous year’sdeterioration of 0.1). Compared to the condition shown in Figure 40, the current situationis extremely worse than this provisional target condition.Figure 41 shows the number of kilometres of road in the different road management re-gions that is unacceptable (according to the provisional disgrace level recommended in thisreport). Andel av det statliga belagda vägnätet som (redan sommartid) överskrider ojämnhetsnivån IRI = 3 mm/m 100,0% 90,0% 80,0% 70,0% 60,0% 50,0% 40,0% 30,0% 20,0% 10,0% 0,0% Vägar med färre än 2000 bilar per dygn Vägar med fler än 2000 bilar per dygnFigure 40 Paved state roads with unacceptable roughness, more than IRI20 = 3 mm/m. Data applies to the road network condition during summer, without frost-related additional roughness such as during the spring thaw. Data is given in blue for roads with an AADT less than 2000, and in red where the AADT is over 2000. 63(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E Längd [km] av statliga belagda vägnätet som överstiger ojämnhetsnivån IRI = 3 mm/m 5000 4000 3000 2000 1000 0 M No M St Sy Vä Sk itt äla oc dö ån st rr kh rd st e olm ale nFigure 41 Total length [km] of road stretches with roughness over IRI20 = 3 mm/m in the summer per Swedish road management region7.2 Variations in the road crossfall are particularly hazardousAccording to a current proposed revision7 of ISO 2631 [10], the natural frequency of atypical human spine on the X-Y axis is about 2.1 Hz. It is therefore extremely importantthat humans are not exposed to strong vibrations at frequencies around 2.1 Hz in or acrossthe direction of travel.As seen in section 4.5, heavy vehicles start to sway on their own if they are exposed to rollat frequencies under 3 Hz. Roll with frequencies under 5 Hz do not occur when travellingon ”normal” roads and at normal speeds. Therefore, in practice, vehicle manufacturers donot focus much attention on the problem of roll resonance. According to a leading truckmanufacturer, there is a theoretical possibility, by designing the vehicle with an extremelylow roll stability. However, this would mean very poor cornering stiffness, and thus a majortendency to capsize in connection with lateral manoeuvres, which is unacceptable from aroad safety perspective and therefore impossible to implement in practice.The mechanical impact of vibrations, distributed over the vibration frequencies, for a truckin good condition with a loaded/unloaded trailer is shown in Figure 42 and Figure 43.When the truck is driven unloaded, a peak can be seen in the Y-direction (across the direc-tion of travel) just in the 1.5 – 2.5 Hz range, i.e. exactly around the natural frequency of thelumbar region of the back. Where the truck is loaded, the effect in this frequency range isless. See the red circle in each figure.The conclusion is that the crossfall variations on badly deformed Swedish roads means thatthese are no longer satisfactory surfaces on which to drive normal heavy vehicles.7Translation comment: the proposal has been adopted as a draft upcoming part of the 2631 standard, enti tled ISO/DIS 2631-5 ”Me-chanical vibration and shock - Evaluation of human exposure to whole-body vibration – Method for evaluation of vibration contain-ing multiple shocks”. 64(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 42 Power spectral density at the driver’s seat in an unloaded truck (in good condition) [64] 65(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31EFigure 43 Power spectral density at the driver’s seat in a loaded lorry (in good condition) [64] 66(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E7.3 Methods to reduce whole-body vibration in connection with road transportSection 26 of the Swedish Road Act [21] stipulates that the road manager must ensureroads are kept “at a satisfactory standard for transport and communication” through main-tenance and repair. It could also be of interest to discuss other ways of reducing vibrationthan through more road maintenance and repair (and greater focus on roughness reductionmeasures, particular using state of the art CAD/CAM technique [63]).7.3.1 Changed travel speedsNeedless to say, no vibrations are generated from road roughness when the vehicle isstanding still. IRI, the road roughness indicator, is calculated at a simulated speed of 80km/h. It would therefore be reasonable to think that road roughness (a road with high IRIvalues) could be compensated through slowing down8 and thereby improve the ride quality.However, when speed data was correlated with roughness data at VTI, it was found thatdrivers showed very little tendency to slow down on rough roads.Figure 37 shows that the vibrations in the vehicle and its suspension are not actually a func-tion of the travel speed itself, but only of the wavelength (which determines the frequencyof the vibrations) and amplitude (determines the vibration effect at a given frequency) ofthe roughness. However, the frequency that occurs when driving over a specific irregularitydepends on the travel speed. Thus, speed can have an indirect effect on the vibration level,depending on the type of road roughness. The faster one drives, the more the longer wave-lengths will be able to affect the movement of the vehicle body and suspension.The roughness found on roads has all kinds of different wavelengths. Since the amplitudegenerally is greater for longwave roughness, the vibration energy in most cases will increaseas speed increases. This is not, however, self-evident, but actually is due to the over-representation of large amplitudes in the longwave road roughness. With modern tech-niques, these can now be efficiently measured and remedied at road repairs. See [63]. Theresonance phenomenon means that it can be better to actually increase the speed in certaincases - particularly on roads with shortwave roughness. See section 7.1.A speed reduction model would be a helpful tool in road management to be able to takethe effects of existing roughness into consideration. However, such a model would have toconsider the mechanical properties of the vehicle in addition to both the amplitude andwavelength of the road roughness. This kind of speed model is shown in Figure 44 forvehicles like the ”Golden Car”, which is used to calculate the IRI value, in other words, atypical passenger car. The model is based on the physical relationship between vertical vi-bration and the IRI value at different effect density spectra for road roughness, while a p-plying restrictions for the vibration level. The model is based on the assumption that thegraph in the effect density spectra for road roughness can be described by a gradient coef-ficient. See ISO 8608 [5].Figure 44 shows that when travelling by car at parking speed on a road with predominantlyshortwave road roughness, a sense of discomfort starts at an IRI = 2.5 mm/m. If instead8Translation comment: In a recent paper ”International Roughness Index, IRI, and ISO 2631 Vibration Evaluation” by Kjell Ahlin &Johan Granlund, it has been analytically proved that speed must be reduced to levels below 20 – 40 km/h to bring substantial ride qualityimprovement. Some of the analysis done when preparing the paper work can be seen in Figure 44. 67(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31Ethe road has predominantly longwave roughness, an IRI up to 10 mm/m can be tolerated.If the speed is increased to 140 km/h, the longwave roughness cannot exceed an IRI above1.6 mm/m. However, at the same speed, shortwave roughness with an IRI = 2 mm/m canbe tolerated without discomfort.The conclusion is that even longwave roughness must be eliminated in an efficient roadtransport system. Högsta komfortabla hastighet i "The Golden Car" Olika samband vid olika lutning för grafen i PSD-diagrammet för vägojämnhetsprofilen 140 120 Hastighet [km/tim] 100 -2,5 (0,63) -2,0 (0,63) 80 -1,5 (0,63) -2,5 (0,315) 60 -2,0 (0,315) -1,5 (0,315) 40 20 0 0 1 2 3 4 5 6 7 8 9 10 IRI-värde [mm/m]Figure 44 Vertical vibration-related speed model. The steepest lines refer to roads with a large predominance of shortwave roughness, and the flattest to roads with predominantly longwave roughness. Vibration limits of 0.315 and 0.63 m/s2 were used in the figure. Source: Study in progress at the SNRA involving a general review of cause and effect.At the time of writing, the speed limit on National Highway 90 between Näsåker andSkarped is 90 km/h. Figure 44 shows that cars should not be driven at a higher averagespeed than 65 - 80 km/h, with the roughness that occurs there, and not faster than about20 km/h (if that) on the stretches where the roughness is greatest. Heavy trucks are about 2- 3 times more sensitive than cars to increased road roughness. Speed reductions wouldincrease transport times drastically -- and thus transport costs -- for the private sector. Asan example of the significance of transport costs in national economy, mention can bemade of how the forestry industry has already declared that the loading and transport ofraw products accounts for as much as 20% of their refinement value.As significant roughness does not exist everywhere along a road, the method of reducingexposure to vibration through changes in speed means that the driving rhythm will bemore affected than the average speed. An irregular driving pattern is both dangerous intraffic (encourages reckless overtaking, heavy vehicles have to brake more than cars atrough spots) and is more harmful to the environment. 68(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E7.3.1.1 Low-frequency (motion sickness) vibrationsFormula 5 shows that at speeds under 30 km/h, roughness where the wavelength is greaterthan 10 m (which is the longest wavelength within which we know from experience that athin new wearing course layer alone can noticeably reduce roughness) will cause such lowfrequency motion that the vibration frequencies will be less than 0.1 Hz. As far as weknow, such low frequency vibrations have no effect on humans. The question is, however,whether road users will accept driving as slowly as 30 km/h, particularly in long-distanceemergency ambulance transport.7.3.2 Changes in vehiclesDeveloping vehicles that could dampen extremely low frequency (0.1 – 0.63 Hz) randomvibrations does not seem realistic. In practice, it is even very difficult to dampen vibrationswith frequencies below around 5 Hz. The fact is that a very soft suspension design is nec-essary for the natural vibration range to be low enough.Transport needs are not constant, thus changes develop over time. This also means thatunsuitable vehicles (vis-à-vis vibration) are being increasingly used for certain transports;e.g., there is a growing demand for more medical intensive care and monitoring equipmentin ambulances, which means a greater load and that ambulances are starting to resembletruck & bus constructions more and more.In trucks, some of the vibrations transferred through the seat and back rest can be damp-ened to a certain extent by replacing older seats with new, modern ones fitted with im-proved vibration isolators. Reducing vibrations at the floor may bring a change to a spring-mounted cab. This, however, can suppress vibrations that are positive in the sense that theyinform the driver about the movement of the vehicle (thus erasing “road feeling”). Chang-ing to a spring-mounted cab could also possibly increase the low frequency vibrations (in-cluding side-to-side vibrations on roads with damages that include much cross slope vari-ance), through the cab suspension’s own transformation of high-frequency vibrations. Thiscan intensify travel sickness. Both of these side effects are negative from a road safetyviewpoint. Perhaps it would be of more merit to install a Central Tyre Inflation (CTI) sys-tem to regulate tyre pressure during travel. This permits easy reduction of the tyre pressurewhen the vehicle is being driven with a light load or without any load at all, which meansthat the vibrations are not propagated as easily up via the wheel axles and onward into thecab. At the time of writing, this system not being favoured in the preliminary Europeannorm 1032 on vibration emission values in vehicles [73]. The present issue focuses on thedifference between vibrations in wheel axles and the seats, not on the difference betweenthe roughness profile of the road and the vibrations higher up. This plays down the signifi-cance of the wheels.If the road manager were to provide statistics on the wavelength/amplitude characteristicsalong different parts of the road network (through PSD diagrams as per ISO 8608 [5]), oreven better; complete roughness profiles, vehicle manufacturers would be able to custom-ise the mechanical properties to the road roughness encountered by the customer and thespeeds at which s/he intends to drive. Considering the extreme segmentation of the vehiclemarket that this would mean, the price for the relatively limited improvement that could beachieved in this way would probably be very high. 69(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E7.3.3 Road maintenanceIt ought to be an obvious goal that the alignment and roughness on all roads (during theentire year) would be such that driving at normal speeds in vehicles that comply with EUmechanical directives and that have passed vehicle inspection would not cause motionsickness or expose vehicle occupants to vibrations that are uncomfortable, or even injuri-ous. As far as the discomfort limit is concerned, 0.315 m/s2 has been recommended forcars in the project entitled ”Ergonomic vehicle classification” [35].In order to prevent motion sickness, the road roughness index must be acceptable for allwavelengths up to 350 metres [63] and the horizontal curvature must meet the require-ments of motor vehicle traffic. This entails a major need for up-grading/re-construction onroads that originated as cow paths.During the past ten years or so, the SNRA has collaborated with different suppliers to co-develop a CAD/CAM geometric pavement model to optimise “mill and fill” road mainte-nance in the method specifications entitled ”Procedures at road repairs” [63]. Throughsurveying the road geometry, planning the best action to take and using plant and equip-ment as directed, all road roughness known to have a negative impact on people and vehi-cles can be minimised within budget allowances. On roads with poor bearing capacity orfrost damage, a new simple bituminous surface is not cost effective. What is then needed isreconstruction and frost-proofing in spots or along complete road stretches. 70(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E7.3.4 Does the choice of road maintenance strategy matter? Tillståndsutveckling vid två olika underhållstrategier 3,5 3 2,5 Ojämnhet IRI [mm/m] 2 1,5 1 0,5 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Tid [år]Figure 45 Roughness development over years in connection with two different strategies of road maintenance and repair.Figure 45 shows, in principle, the surface condition deterioration caused by traffic load andclimate over the years in connection with two different maintenance strategies. Roadroughness steadily increases from the ideal (green line). The road is repaired when itreaches the intervention level (red line). The one strategy means undertaking few, but dura-ble measures (black graph). The other strategy entails several weak measures (orangegraph). A simple mathematical analysis shows a considerably higher dose of disturbancewhere many, meagre measures are undertaken. Moreover, this entails much greater distur-bance from frequent road works. 71(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E7.4 Conclusions7.4.1 Evaluation of impact on humans of vibrations related to road roughnessThe following is a summary of the conclusions drawn by Prof. Ronnie Lundström of theNational Institute for Working Life, subsequent to having analysed the vibrations measuredin this study:– road roughness has a decisive impact on the vibration load to which the vehicle occupant is exposed in all respects,– when travelling on the old part of National Highway 90 in both the logging trucks and the ambulances, drivers, passengers and patients were exposed to an unacceptably high vibration load,– when travelling on the old part of National Highway 90 and County Road 950• the vibration load is compatible with potential, and sometimes even a probablehealth hazard,• the vibration load is compatible with a considerably higher degree of discomfortcompared to the newer and smoother part of National Highway 90,• the vibration load is compatible with a greater risk of reduced performance ability,• the occupants run a higher risk of developing symptoms of travel sickness thanwhen travelling on the newer and smoother part of National Highway 90,– when transporting patients in a state of health that demands keeping the body completely still, for example in the case of brain, spinal and neck injuries, the ride on the old part of National Highway 90 and County Road 950 generates un- acceptably high vibration levels,– the vibrations registered on the old part of National Highway 90 and County Road 950 have a clear element of shock and rotational motion at levels high enough that they probably exacerbate the risk of injury, discomfort and motion sickness.7.4.2 Assessment of the need to take action on the road network, etc• A reduction in speed of between 30 - 50 km/h in the ambulance resulted in a reduction of discomfort by 0 (zero!) ISO class on the rough test stretch of National Highway 90 and by one (1) ISO class on the smooth part [65].• Changing from a badly run down truck to a new one resulted in a reduction of discom- fort of one (1) ISO class on both test stretches of National Highway 90 [65].• Changing from a lurching intensive care ambulance to a comfortable emergency ambu- lance resulted in a reduction of discomfort of one (1) ISO class on both test stretches of National Highway 90 [65].• In all the trucks and ambulances, driving at a given speed on a test stretch with a “smooth” carriageway, compared to driving on a ”rough” one resulted in a reduction of discomfort of 2 – 3 (!) ISO classes on both test stretches on National Highway 90 [65].• The mechanical properties of the smaller ambulance are comparable to a normal car (see Figure 36). The fact that driving a car 4 hours a day on a carriageway where the roughness is equal to the rough stretches on National Highway 90 means ”potential health risk” [65] is alarming considering the effect on travelling salesmen, taxi drivers, etc. 72(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E• Increased road roughness affects the vibration levels in the cab of a truck about 2-3 times more than in a car.• A considerable amount of the vibration problem is caused by relatively longwave / extremely longwave road roughness and by uneven crossfall. This type of road damage is not shown particularly well by the IRI, which means that objective knowledge about this kind of deterioration is lacking in the SNRA PMS database. Longwave road rough- ness is considered primarily to be caused by settlement. In certain types of soil, this kind of steady damage can continue up to 100 years after the road was first built or most recently strengthened. This in combination can explain why drivers feel that the quality of the ride has deteriorated despite the fact that the IRI statistics remains rela- tively stable.• The problem is greatest during late winter / spring, due to frost heave variance in and under the road structure.• Badly damaged stretches must be completely re-constructed.• Exceptionally sharp curves and steep undulations should be remedied.• Moderately damaged stretches can be repaired, based on ergonomic principles, through the use of the best state of the art technology as in the SNRA’s ”Procedures at road works”, the so-called “mill and fill” CAD-design [63].• A provisional ”disgrace limit” for road roughness is an IRI20 = 3 mm/m, correspond- ing to 6.0 cm accumulated suspension stroke per second during a 72 km/h passenger car ride. The 3 mm/m limit is based on human considerations (risk of injury, reduced performance ability, etc) rather than on potential vehicle damage, etc.• Even in the summer, about one-third of the state road network is in a completely una c- ceptable condition (IRI20 > 3 mm/m).• A special plan of action for repairing the road network will involve extensive amounts of transported road materials. As far as possible, materials from borrow pits should be transported and stored close to road projects during winter, when the roads are frozen and the bearing capacity is good in order to prevent further damage to the roads.• Stretches within each road class where the condition is worse than the disgrace level can only be prioritised according to “worst first”. Otherwise, the disgrace limit princi- ple can be ignored.• One possible alternative on low traffic volume roads is to reconstruct them as gravel roads, which can then be graded regularly.• For now, the ambition is that the IRI20 after remedial works should be less than 1.00 mm/m during unfrozen ground conditions and 1.40 mm/m when the ground is fro- zen. With the exception of the first 100 m on the traffic lane in the direction of travel -- where movement in the body of the vehicle can be caused by damage ahead of the re- pair -- an IRI20 higher than 1.8 mm/m should fail inspection, and the contractor should be required to take the necessary action to rectify this without any additional remunera- tion. This would, however, be under the condition that the road authority had specified that the design should take into consideration all roughness that affects the IRI during each respective season.• In connection with surveys for drawing up design documents for ergonomically correct road maintenance, or when inspecting contract works, etc, the road roughness must be measured with profilometers that can handle wavelengths up to at least 70 m. Also, to be completely able to prevent the risk of motion sickness, it is necessary to be able to measure wavelengths up to some 350 m. Instruments that are unable to meet the envi- ronmentally related needs of road users -- traditional recording coaches, straightedges, yardsticks, visual inspection, etc. -- are completely out of the question for the purposes 73(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E mentioned above. See also the Environmental Code, Instructions on Load Ergonomics published by the National Board of Occupational Safety and Health, Instructions on the design of installations, etc.7.4.3 Need for further research and development• Ensure that any problems (technical, contract, organisation, etc.) that would prevent the full application of the SNRA’s ”Procedures at road repairs” [63] CAD/CAM- technology are eliminated immediately.• Refined limits for road roughness and texture that put human health at risk should be further examined in consultation with the National Institute for Working Life based on the criteria for the combined exposure to vibrations, noise and infrasound for truck drivers driving at legal speeds, and for particularly vulnerable people during emergency transport in ambulances (defined as driving about 25% faster than the posted speed).• Motion sickness is reported much more frequently by medical orderlies and patients in ambulances than by those travelling in cars. A unique motion sickness constant, K m, see formula 7 in [65], should therefore be determined for these particular categories of road user.• Develop different filters9 for the profilometers that replace the IRI value when assess- ing the risk of discomfort, injury and motion sickness. The filters should be used on vehicle models like ”The Golden Car”, but should ultimately process the vibrations in compliance with the Wk and Wf filters in ISO 2631. The assessment of vehicle damage costs, etc should, however, continue to be based on the IRI value (or other unit of measure for suspension vibration that is not filtered with respect to human sensitivity to frequency).• Develop specifications for ergonomically correct geometric design for road mainte- nance purposes. New construction specifications are not completely applicable at the maintenance stage. Examples of questions that need to be answered (see also the fore- going paragraph): ”What roughness can be accepted in different wavelength bands in the longitudinal direction of the road?”, ”How much can the nominal crossfall be a l- lowed to vary along the road?”, ”When is a curve so sharp that it must be straightened out through re-construction?”, ”What nominal crossfall is to apply in existing curves, when these are considerably sharper than what is allowed in the specifications for new construction?”.The possibilities and problems associated with vibration measurements are presented in atechnical report [64]. Any vehicle used for collecting measurement data should be equippedwith a distance meter (like the KUAB road logger, Coralba Digitrip or similar) that can beconnected to a computer when registering data that is to be correlated with the road sur-face condition data stored in the SNRA’s road database. This reduces the work spent oncorrelating data by at least 90%.9 Translation comment: This is done in the recently developed software Ride Quality Meter ® 74(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E8 Reference list[1] Nationalencyklopedin.[2] Sandberg, U. (1998). Influence of Road Surface Texture on Traffic Characteristics Re-lated to Environment, Economy and Safety. Väg- och transportforskningsinstitutet, Notat53A-1997[3] Strandberg, L. (1996). Olycksrisker och bromskraftfördelning i personbilar. Väg- ochtransportforskningsinstitutet, Meddelande 768-1996[4] Harris, G.J. & Nelson, P.M. (1999). Control of body noise from commercial vehicles.TRL Journal of Research 1999, vol 2, no 1[5] Mechanical vibration - Road surface profiles - Reporting of measured data. (1995). In-ternationell standard, ISO 8608:1995[6] Trafikantbetyg. Vägverket. Årliga rapporter under perioden 1995-98 från IFS AB tilltrafikantavdelningen.[7] Vibration och stöt - Vägledning för bedömning av helkroppsvibrationers inverkan påmänniskan – Del 3: Inverkan på människan av vertikala helkroppsvibrationer i z-riktningen inom frekvensområdet 0.1 – 0.63 Hz. (1985). Svensk och internationell stan-dard, SS-ISO 2361/3[8] Granlund, J. (1996). Funktionsmätning på väg – med Laser RST mätbilar. ISSN 0349-6023. Luleå Tekniska Högskola.[9] Tekniska NomenklaturCentralen. http://www.tnc.se[10] Vibration och stöt - Vägledning för bedömning av helkroppsvibrationers inverkan påmänniskan – Del 1: Allmänna krav. (1998). Svensk och internationell standard, SS-ISO2361/1[11] Griffin, M.J. (1990). Handbook of Human Vibration. Human Factors Research Unit,University of Southampton.[12] Gillespie, T.D. & Sayers, M.W. (1983). Guidelines for the Conduct and Calibration ofRoad roughness Measurements. Supplementary report to the World Bank, WashingtonD.C.[13] Karamihas, S.M. & Sayers, M.W. (1997). The Little Book of Profiling. University ofMichigan. http://www.umtri.umich.edu/erd/roughness/litbook.html[14] Magnusson, G. (1993). Metoder och instrument för mätning av egenskaper som ärviktiga för vägytans funktion. Väg- och transportforskningsinstitutet, Opublicerat manu-skript 75(79)
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    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E[36] Förstberg, J. (1998). Varför kan man bli åksjuk när man åker tåg? Väg- och trans-portforskningsinstitutet, Särtryck 296-1998[37] Årsredovisning 1998. (1999). Vägverket, Publ. 1999:33. http://www.vv.se/[38] Arnberg, P.W. & Åström, G. (1979). Vägojämnheters inverkan på bilförares presta-tion och trötthet. Statens väg- och trafikinstitut, Rapport 181-1979[40] Meriam, J.L. & Kraige, L.G. (1987). Engineering Mechanics, vol. 2, Dynamics. JohnWiley & Sons, New York.[41] Automobile Ride, Handling, and Suspension Design. (1996). Robert Q Riley Enter-prises. http://www.rqriley.com/suspensn.html[42] Evaluation of vibration. (1999). Ergotech company.http://www.ergotech.co.za/vib_wbv.htm[48] Weigh-In-Motion of Road Vehicles. (1999). European Commission, Directorate Gen-eral Transport. COST Action 323. http://www.cordis.lu/cost-transport/src/cost-323.htm[51] Helkroppsvibrationer: Stötar och icke-harmoniska vibrationer. Förekomst samt effek-ter på människan. (1986). Arbetarskyddsstyrelsen, Slutrapport ASF 78-1550[52] Arbetarskyddsstyrelsens föreskrifter om belastningsergonomi. (1998). Arbetarskydds-styrelsen, AFS 1998:1 http://www.arbsky.se/afs/1998_01.pdf[53] Ont i ryggen. (1991). Statens beredning för medicinsk utvärdering. http://www.sbu.se/[54] Dana, H.J. (1933). The Dana Automatic Recording Roughometer for MeasuringHighway Roughness. Highway Research Board, Proceeding[55] Cebon, D. (1999). Handbook of Vehicle-Road Interaction. University of Cambridge,England.[56] Dana, H.J. (1930). Formation of Washboards in Gravel Highways. Highway ResearchBoard, Proceeding[57] Nilsson, L-E. et al. (1989). Trafikledsteknik, del 1: Vägar, gator, trafik & miljö.Institutionen för vägbyggnad, Chalmers Tekniska Högskola.[58] Sylwan, O. (1937). Lyx och komfort. Svenska Humanistiska Förbundet.[59] Widding, L. et al. (1996). Svenska äventyr, 1710 - 1780.[60] Buckle, P. et al. (1980). Factors influencing occupational back pains in Bedfordshire.Spine 5.[61] Tengström, E. (1991). Bilismen – i kris? Rabén & Sjögren. 77(79)
    • Whole-body vibration when riding on rough roads SNRA Publ. no. 2000:31E[62] Nationell plan för vägtransportsystemet 1998 - 2007. (1998). Vägverket, förslag[63] Vägbanemodell för datorstödd utformning av underhållsbeläggningar. (1999). Väg-verket, publ 1999:100 http://www.vv.se[64] Ahlin, K. (2000). Helkroppsvibrationer vid färd på ojämna vägar. IngemanssonTechnology AB, Mät- och Analysrapport S-13542-r-A http://www.ingemansson.com[65] Lundström, R. (2000). Helkroppsvibrationer vid färd på ojämna vägar - en förstudie.Arbetslivsinstitutet, tekniska enheten, uppdragsrapport 2000:1. http://umetech.niwl.se/[66] Gillespie, T.D. et al. (1982). Truck Cab Vibrations and Highway Safety. HighwaySafety Research Institute, University of Michigan. FHWA report RD-82/093[67] Life-Cycle Cost Analysis in Pavement Design. US Department of Transportation,Federal Highway Administration. Publication No. FHWA-SA-98-079http://www.fhwa.dot.gov[68] Hegmon, R. R. (1993). A close look at Road Surfaces. Public Roads.http://www.tfhrc.gov/pubrds/summer93/p93su4.htm[69] Hedberg, G.E., et al. (1991). Mortality in circulatory diseases, especially ischemic heartdisease, among Swedish professional drivers. J Human Ergol., 1991;20:1-5[70] Hedberg, G.E., et al. (1993). Risk indicators of ischemic heart disease among maleprofessional drivers in Sweden. Scand. J Work Environ Health, 1993;19:326-33[71] Hedberg, G.E. & Langendoen, S.M. (1989). Factors Influencing the turnover of Swed-ish Professional Drivers. Scand. J Soc Med, 1989;17:231-237[72] Landström, U. & Löfstedt, P. (1987). Buller, vibrationer och vakenhet under last-bilskörning. Arbete och hälsa, 1987:41[73] Mechanical vibration - Testing of mobile machinery in order to determine the vibra-tion emission value. (2000). Preliminär Europanorm, prEN 1032[74] Bovenzi, M. & Hulshof, C.T.J. (1999). An updated review of epidemiologic studies onthe relationship between exposure to whole-body vibration and low back pain (1986-1997).Int Arch Occup Environ Health (1999) 72:351-365[75] Spång, K. (1997). Assessment of whole-body vibration containing single event shocks.Noise Control Eng. J., 45(1), 1997, pp 19-25. 78(79)
    • SE-781 87 BorlängeTelephone +46 43-750 00. Fax + 46 243-753 25. Text telephone +46 243-750 90 E-mail: vagverket@vv.se / Internet: www.vv.se