1st INTERNATIONAL SYMPOSIUM ONFREEWAY AND TOLLWAY OPERATIONS           TRB Freeway Operations Committee                   ...
Setting speed limits: a complex trade-off     safety, environmental                                          mobility     ...
Objectives• Investigate drivers’ speed choice behaviour and  their attitudes towards speed limits• Review the current prac...
Drivers’ speed choiceMost drivers select a reasonably safe speed for the conditionsunder which they travelThey select thei...
Driver speeds in the trunk road network in Greece Surveys in the context of the research project “Method for Setting Relia...
Motorway with local speed limit 90 km/h
Probability distribution of observed speeds in      motorwaydistribution ofwith local speed limitwith speed        probabi...
Motorway with general speed limit 120 km/h
Probability distribution of observed speeds in motorway    Cumulative probability distribution of observed speeds in the l...
Roadside surveys• Self reported speed and relation to drivers’  characteristics• Drivers’ attitudes towards speed limits
Self reported speeds in motorways with general         Histogram and cumulative probabality distribution of self reported ...
Self reported speed and driver’s age      in motorways with general speed limit 120 km/h                = < 80istribution ...
Self reported speed and vehicle engine’s power      in motorwaysreported speed in motorways with speed limit120 km/h      ...
Self reported speed and frequency of use      in motorways with general speed limit 120 km/h         Distribution of self ...
Relationship between self reported speed and personal                characteristics of driversReference values:          ...
Exceeding the motorway speed limit:       Factors affecting driver choices       Binary logit coefficients                ...
Reasons that car drivers conform with the         motorway general speed limit (120km/h)                                  ...
Reasons that drivers exceed the motorway general                speed limit (120km/h)                                     ...
Drivers’ views on the 120km/h general speed limit on                     motorways                 Drivers views on the le...
Should drivers exceed speed limits?                     Speed limits should never be                      Speed limits sho...
Should drivers exceed speed limits?                 Current Speed limits are lower than the limit                 for safe...
Should drivers exceed speed limits?                              Speed limits are inaccurate                     Drivers c...
Main findings from surveys Current speed limits are exceeded by the vast majority of drivers. Speed limit offenders are mo...
Reasons for regulating drivers’ speedSelf optimum speed : Driver tries to minimise                          travel time,  ...
Different approaches in setting speed limits                  (Fildes et al. for Austroads 2005)Engineering  Road geometry...
Economic optimisation approach                (EU-MASTER, Cameron)Explicit framework that takes account of :•   Road accid...
Road accident costs              AccC =         Σi   NiA * VAcciwhereNA      the number of accidents of category iVacc the...
The number of Road accidents                     (Nilsson (1984)      NA = (VA/VB)p * NBNA = number of accidents After the...
Travel time costs    TimC = Traffic Volume * Travel Time * VoTrequires reliable estimates of the value of timeVehicle oper...
Traffic emissions costsAtmospheric emission pollutants which are normally regarded asthe ones of most concern include:    ...
Traffic emissions costs EmisC = Σi Volume Pollutanti * CoPiwhereCoPi the cost of pollutant i.  Traffic emission impact dep...
Noise pollution impactDepends on the size of the population living in the vicinityof the road, and who are exposed to nois...
Speed limits, speed distribution and speed enforcement                                             Low/moderateAll relatio...
Future researchFurther research in• Effect of level of enforcement on speed distribution• Speed – accident relationships• ...
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Driver's Attitudes toward Speed Limits

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Findings of greek driver's attitudes toward speed limits.

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Driver's Attitudes toward Speed Limits

  1. 1. 1st INTERNATIONAL SYMPOSIUM ONFREEWAY AND TOLLWAY OPERATIONS TRB Freeway Operations Committee Athens 2006SPEED LIMITS: planning perspectivesand drivers’ attitudes in Greece Petros Vythoulkas Basil Psarianos Pavlos ChorianopoulosFaculty of Rural and Surveying EngineeringNational Technical University of Athens Eva KasapiMinistry of Environment, Regional Planning and Public Works
  2. 2. Setting speed limits: a complex trade-off safety, environmental mobility and and economic energy costs costs speed• Speed may affect the severity and risk of accidents.• But unreasonably low speed limits increase drivers’ violation of the speed limits
  3. 3. Objectives• Investigate drivers’ speed choice behaviour and their attitudes towards speed limits• Review the current practices in setting speed limits.• Directions for future research
  4. 4. Drivers’ speed choiceMost drivers select a reasonably safe speed for the conditionsunder which they travelThey select their self-optimum speed primarily on the basis of Travel time minimisation Accident risk minimisation Minimisation of the Risk of being caught speeding Fuel economyThe self-optimum speed is related to driver’s Personal characteristics age, income, driving experience, risk behaviour, environmental awareness Journey characteristics
  5. 5. Driver speeds in the trunk road network in Greece Surveys in the context of the research project “Method for Setting Reliable Speed Limits in Greece” funded by the Ministry of Environment, Regional Planning and Planning Works. Speed choices are analysed based : a) on actual speed data collected through the use of radar meters at 15 stations along the rural highway network of Greece. b) on a dataset collected through a questionnaire survey that was conducted at 5 motorway toll plazas in Greece.
  6. 6. Motorway with local speed limit 90 km/h
  7. 7. Probability distribution of observed speeds in motorwaydistribution ofwith local speed limitwith speed probability section observed speeds in motorway 90 km/h limit 90 km/h histogram Cumulative Probability Distribution25% 120% 21%20% 100% 85% 80%15% 12% 12% 60% 11% 11%10% 8% 7% 7% 40% 5%5% 3% 2% 20% 2% 0% 0% 1,5%0% 0% 85 90 95 100 105 110 115 120 125 130 135 140 145 150 observed speed Speed limit V85 = 127 km/h
  8. 8. Motorway with general speed limit 120 km/h
  9. 9. Probability distribution of observed speeds in motorway Cumulative probability distribution of observed speeds in the left with general speed limit 120 km/h and right lane of motorway with speed limit 120 km/h120%100% 85% 80% Left lane 60% Right lane both lanes 40% 31,7%19,3% 20%5,6% 0% 90 100 110 120 130 140 150 160 170 180 190 200 Speed limit 140 152 157 Speed (km/h)
  10. 10. Roadside surveys• Self reported speed and relation to drivers’ characteristics• Drivers’ attitudes towards speed limits
  11. 11. Self reported speeds in motorways with general Histogram and cumulative probabality distribution of self reported speeds in speed limit 120km/h motorways with with speed limit 120 km/h Histogram Cumulative probability distribution35% 120% cumulative probability distribution30% 100% 29% 26%25% 80%20% 60%15% 40%10% 12% 8% 5% 20%5% 6% 6% 3% 1% 1% 1% 1% 0% 0%0% 0% 70 80 90 100 110 120 125 130 135 140 150 155 160 170 180 190 200 220 V85 = 140 ~150 km/h self reported speed (km/h)
  12. 12. Self reported speed and driver’s age in motorways with general speed limit 120 km/h = < 80istribution of self reported speed in-motorways with speed limit 120 km/h101 -age D km/h 81 100 km/h by drivers 120 km/h 121 - 130 km/h 131 - 140 km/h > = 141 km/h50% 46% 42% 41%45% 37%40% 34% 34% 32%35% 31% 27%30% 25% 25% 24% 24% 23%25% 18% 17% 16%20% 15% 14% 13% 14% 13% 11% 11%15% 10% 9%10% 5%5%0% 18 - 24 25 - 34 35 - 44 45 - 54 55 - 64 > 65 Sample drivers age
  13. 13. Self reported speed and vehicle engine’s power in motorwaysreported speed in motorways with speed limit120 km/h Distribution of self with general speed limit (120 km/h) by vehicle engine size = < 80 km/h 81 - 100 km/h 101 - 120 km/h 121 - 130 km/h 131 - 140 km/h > = 141 km/h70% 64%60% 50%50% 43%40% 34% 29%30% 25% 26% 20% 21%20% 17%10% 7% 8% 9% 7% 7% 8%0% <= 1100 1101 - 1400 1401 - 1800 1801 - 2300 > 2300 sample
  14. 14. Self reported speed and frequency of use in motorways with general speed limit 120 km/h Distribution of self reported speed in motorway and trip frequency < 110 km/h 110 - 130 km/h > 130 km/h80%70% 67% 63%60% 57% 53% 49% 46%50% 42% 44% 43% 41% 44%40% 36% 30%30% 20%20% 14% 16% 13% 7% 10%10% 5% 3%0% almost 1 - 2 days/ once in a once a several 1 - 3 times Sample every day week fortnight month times a a year year
  15. 15. Relationship between self reported speed and personal characteristics of driversReference values: Linear regression coefficients- Age > 65 Coef value t (Constant) 109,94 13,19- Engine =< 1100 cc AGE 18 - 24 29,961 5,22- Frequency 1- 3 /year AGE 25 - 34 27,864 5,85- Gender male AGE 35 - 44 19,266 4,04- Not involved in accident AGE 45 - 54 21,596 4,56 AGE 55 - 64 20,229 4,10- No speeding ticket ENGINE > 2300 cc 24,926 3,61- Do not consider safety Frequency: Almost every day 6,593 1,82as a reason for GENDER -6,011 -1,93conforming with speedlimit Involvement in an accident -5,214 -1,95 Speeding ticket in the last 5 years 6,529 2,75 Safety is a reason for conforming with speed limit -11,127 -4,01
  16. 16. Exceeding the motorway speed limit: Factors affecting driver choices Binary logit coefficients β Sig.AGE 18 - 24 1,551 0,005AGE 25 - 34 1,3 0GENDER (0:male, 1:female) -0,826 0,033ENGINE > 2300 cc 2,64 0,014ENGINE 1801 – 2300 cc 0,946 0,014ENGINE 1401 – 1800 cc 0,601 0,023SPEEDING TICKET 0,967 0,001SAFETY is a reason forconforming with the speed limit -1,002 0
  17. 17. Reasons that car drivers conform with the motorway general speed limit (120km/h) Driver’s speedReasons for conforming with % of Drivers whospeed limit drivers Conform with Others F sig speed limitSafety 76,2% 128 142 23,4 0Risk of getting a speedingticket 25,5% 130 136 4,929 0,02Legislation 14,3% 131 131 0,005 0,94Fuel cost 4,4% 127 131 0,573 0,45Driver is not in a hurry 4,1% 121 132 3,059 0,81Environmental 1,4% 122 131 0,695 0,40Other reasons 1,4% 127 131 0,128 0,72Drivers who stated thatthey do not conform withthe 120km/h speed limit inmotorways 3,4% 160 130 20,26 0
  18. 18. Reasons that drivers exceed the motorway general speed limit (120km/h) Drivers whoReasons for exceeding the % of exceed the Others F sig.speed limit drivers speed limitBeing in a hurry 42,9% 131 131 0,01 0,91The limit for safe driving is higherthan 120km/h in motorways 31,3% 138 128 13,1 0Other reasons 24,5% 134 131 0,36 0,55Adjusting to the speed of othervehicles 5,1% 132 131 0,02 0,89Enjoy speeding 4,8% 149 130 10,1 0,00Being bored driving at low speed 4,8% 147 131 8,1 0,01No specific reason 3,4% 133 131 0,11 0,74Never/rarely exceed the speedlimit 24,5% 116 136 56,5 0
  19. 19. Drivers’ views on the 120km/h general speed limit on motorways Drivers views on the level of speed limit in motorways (120km/h) 70% 65% 150 60% mean speed (km/h) 138 140% of drivers 50% 40% 130 31% 30% 120 112 120 20% 110 10% 5% 0% 100 Its very high and Its about right Its very low and should be decreased should be increased
  20. 20. Should drivers exceed speed limits? Speed limits should never be Speed limits should never be exceeded exceeded 45% 160 42% 40% 152 35% 150 35% mean speed (km/h) 30%%Drivers 139 140 25% 131 20% 126 130 15% 10% 10% 8% 120 5% 114 5% 0% 110 Strongly Agree Neither Disagree Strongly Agree agree not Disagree disagree
  21. 21. Should drivers exceed speed limits? Current Speed limits are lower than the limit for safe driving andkm/h or more 10 thus could be exceeded Speed limits are lower than the speed limit for safe driving, and thus they could be exceeded by by 10 km/h or even more 60% 151 160 50% 150 46% 137 138 mean speed (km/h) 140 40%% of Drivers 36% 124 130 30% 120 20% 110 14% 100 10% 100 2% 2% 0% 90 Strongly Agree Neither agree Disagree Strongly Agree not disagree Disagree
  22. 22. Should drivers exceed speed limits? Speed limits are inaccurate Drivers can judge forare inaccurate Speed limits themselves whether Drivers can judge whether they can drive slowly or fast . they should drive slowly or fast 70% 160 60% 150 59% 150 mean speed (km/h) 50%% of drivers 137 140 40% 134 130 30% 130 123 20% 18% 12% 120 10% 9% 2% 0% 110 Strongly Agree Neither agree Disagree Strongly Agree not disagree Disagree
  23. 23. Main findings from surveys Current speed limits are exceeded by the vast majority of drivers. Speed limit offenders are mostly Young drivers, Frequent users and drivers of high engine power cars. Safety is the main reason for conforming with speed limits. Being in a hurry is the main reason for exceeding speed limits. ~40% of drivers consider current speed limits as lower than the limit for safe driving, and believe that speed limits could be exceeded by 10km/h or more.
  24. 24. Reasons for regulating drivers’ speedSelf optimum speed : Driver tries to minimise travel time, perceived risk of accident perceived risk of being caught fuel cost drivers can impose significant risks Social optimum and uncompensated costs on others Different drivers have different risk Cost of travel time tolerances Accident costs May have inadequate information and/or misjudge roadway conditions, Environmental costs and own and vehicle capabilities Energy costs May misjudge the effect speed on Enforcement cost accident probability and severity
  25. 25. Different approaches in setting speed limits (Fildes et al. for Austroads 2005)Engineering Road geometry, Traffic speeds, Accident data, Traffic volumes, Roadside development.Drivers’ Choice Drivers select a reasonable and safe travel speed. The posted speed limit is the 85th percentile driving speed.Economic Optimisation All costs (travel time, injury, death, environmental, energy) associated with travel are expressed in monetary terms. The posted speed limit is the speed that results in the lowest cost.Harm Minimisation Life and health cannot be measured in monetary terms. Fatalities or serious casualties is not considered as an inevitable cost of increased mobility.
  26. 26. Economic optimisation approach (EU-MASTER, Cameron)Explicit framework that takes account of :• Road accident costs AccC• Travel time costs TimC• Vehicle operating costs OpC• Traffic emissions costs EmisC• Noise pollution costs NoisC
  27. 27. Road accident costs AccC = Σi NiA * VAcciwhereNA the number of accidents of category iVacc the cost of an accident Estimation of a fatal accident cost is a controversial issue Different methods Human Capital Approach Willingness to Pay can lead to significantly different costs of accidents
  28. 28. The number of Road accidents (Nilsson (1984) NA = (VA/VB)p * NBNA = number of accidents After the speed changeNB = number of accidents Before the speed changeVA = mean or median speed AfterVB = mean or median speed Before p = 4 for fatal accidents 3 for serious injury accidents 2 for minor injury accidentsPoor estimates of NB can result in highly inaccurate estimates ofNA, particularly in the case of fatal accidents where p = 4Speed variance is also considered as an important factor
  29. 29. Travel time costs TimC = Traffic Volume * Travel Time * VoTrequires reliable estimates of the value of timeVehicle operating costs OpC = Traffic Volume * distance * Fuel Consumption * fuel cost - Reliable Fuel consumption functions are available for different types of vehicles - Fleet composition data should be available
  30. 30. Traffic emissions costsAtmospheric emission pollutants which are normally regarded asthe ones of most concern include: Euro III_< 1.4 l Euro III_1.4 - 2.0 l Euro III_> 2.0 l • Hydrocarbons and other organic compounds (VOC), Euro IV_< 1.4 l Euro IV_1.4 - 2.0 l Euro IV_> 2.0 l benzene, 1,3-butadiene 0,8 NOx emissions rates • Carbon monoxide CO 0,7 • Nitrogen Oxides NOx 0,6 • Particular Matter (PM) – Ν Ο x e m i s s i o n s (g r / k m ) 0,5 particles emitted from the 0,4 exhaust 0,3 • CO2: is a main contributor to global warming. 0,2 0,1Extensive database of vehicleEmission functions is provided by 0,0 0 0 20 20 40 40 60 60 80 100 120 140 160 180 80 100 120 140 160 180the UK Dept of Environment Speed (km/h) speed (km/h))
  31. 31. Traffic emissions costs EmisC = Σi Volume Pollutanti * CoPiwhereCoPi the cost of pollutant i. Traffic emission impact depends on • the size of the population living in the vicinity of the road, and who are exposed to emissions, and • the emission concentration which the population is exposed to. Pollutant concentrations at the road side receptors should be estimated by taking into account the dispersion and dilution of the pollutants. Vehicle fleet composition Cost of different pollutants has not been estimated in Greece
  32. 32. Noise pollution impactDepends on the size of the population living in the vicinityof the road, and who are exposed to noise.Noise level depends on speed, traffic volume and form ofroadside development - Estimation of noise level is acomplex problem often requiring specialised SWCost and effectiveness of noise barriers should becompared to cost of reduced mobility due to speedreductionCost of noise pollution – hedonic pricing applied in urbanareas, WTP approachesNoise pollution cost has not been estimated in Greece
  33. 33. Speed limits, speed distribution and speed enforcement Low/moderateAll relationships for estimating enforcementsafety, environmental, energy andmobility implications are based ondriver speeds - not speed limits.Nonlinear relationships imply thatspeed distributions rather thanmean speed values should beused. f( E[v] ) ≠ E[ f(v) ] IntenseAccident frequency is related to enforcementspeed variance.Intensity of speed enforcementaffects speed distributionBut cost of intensive enforcementcan incur high costs Speed limit
  34. 34. Future researchFurther research in• Effect of level of enforcement on speed distribution• Speed – accident relationships• Reliable estimates of accident, pollution costsComplexities and uncertainties related to the estimation of themonetary values of the various benefits and disbenefits fromspeed changes dictate that alternative options that couldimprove accident rate should always be considered beforeproceeding to speed limit changes.
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