Reducing Health and Safety Riskson Poorly Maintained Rural RoadsJohan Granlund, MSc, IPMA BChief Technology OfficerVectura Consulting AB, Sweden
Lateral forces and low / split friction really don´t mix well [Photo: Torbjörn Elverheim] [Photo: Niclas Thunborg] Instability crashes are not randomized.
The paper in a nutshellDisproportionate risk on rural low volume roads.NVF statement on need of actions to mitigate over-risks.Health and safety issues raised by high ride vibration.Roadex-project case study on the Beaver Road 331.Identifying road features decisive for risk factor such as:• lateral force,• poor road surface drainage, and• low friction; often in combo with split friction,using available data from road profilers.
Disproportionate risks in the rural EU Northern Periphery153 % higher risk to die in a vehicle crash in rural NP areas, than in metropols Stockholm, Gothenburg & Malmoe. [Photo: Torbjörn Elverheim]NP road crashes take 39 % more lives than the worst therapeutically treatable “big killer” Diabetes Mellitus.Truckies 3 times higher prevalence of heart disease.
Nordic Road Association Statement“-There is a need to implement new knowledge and practical methods into new approaches, aiming to make an efficient reduction of the disproportionally high health and safety risks on hot spot sections on the road network.This will improve the working environment for professional drivers and is expected to reduce crash risk for both heavy vehicle and light vehicle traffic as well”. NVF Working Group on Vehicles and Transportation Helsinki 2010-02-02
Health and safety issues raised by ride vibration Road Feel Driver’s Performance Vibration Driver Response Accident Potential Vehicle Performance Driver/Vehicle Ride Excitation Ride Environment Driver Response Accidents Performance Low Level, Physical (Biodynamic) Potentially Influenced by Multi-Modal Vibration Driver Distributed Response – Vibration of Roughness - Visual Acuity -Prefatigue Vigilance Severe, Dominant Frequencies Body Parts and Organs Localized 1 to 10 Hz - Reaction Times Physiological Effects - Fatige-decreased Vigilance - Tracking and other Frequency Dominant Amplitudes eg. Visual Motor Tasks -Drivers’ Modulation of SteeringSpeed Influence up to 2 m/s2 Cardiovascular and Brake Controls Amplitude Rattling Control Vehicle - Driver Affected by Ailments Vehicle has: Instruments and Mirrors Psychological Effects eg. Discomfort - Road Holding - Image Clarity in Mirrors • Variable Payload Possible Momentary Stress - Component Wear • Stiff Suspension -”Unseated” Driver by Severe Jolt ”Unseating” of Driver - Component Failure • Dry Friction in the Springs Pathological Effects - Vehicle Road-Holding • Flexible Frame eg. Back Pain Performance • Multiple Coupled Masses • Rotating Nonuniform Components [Highway Safety Research Institute]
2002/44/EC Physical Agents Directive - VibrationIf the truck drivers exposure exceeds the Action Value A(8)= 0.5 m/s2, the employer is obliged by law to take measures to minimize vibration exposure.
EU Roadex III project case study on the Beaver Road 331A regional 170 km route across Västernorrland, Sweden.Annual Average Day Traffic, AADT, 350 to 2000 veh/day.Speed limits 90 and 70 km/h.
Mounting truck ride sensorsTest truck Scania R480 164 G 6x4, GVW 60 ton incl trailer. Z-axis 1 kHz at L and R frame and at front wheel axle. GPS + 6-axis 100 Hz inertial unit in the cab. X, Y, Z-axis 1 kHz seat pad.Camera for right of way.Mic for interior noise.
Daily Vibration Exposure A(8) Daily vibration exposure A(8) Scania R480G 6x4 timber logging truck Route, 8 h morning shift: Ramsele - Backe (unladen), Forest Road, Backe - Stavre - Ortviken (loaded), Ortviken - Backe (unladen), Backe - Ramsele (loaded) and some misc driving. 0,90 0,76 0,80 0,70 0,60 Vibration [m/s2] 0,50 0,50 Current exposure 0,40 EU Action Value 0,30 0,20 0,10 0,00Results for normal driving shifts, taking roundtrips from the Forests to the Coast:A(8) = 0.76 m/s2, over EU Action Value A(8) = 0.5 m/s2.
Reference road measurement [Photo: Mats Landerberg]• Road alignment (curvature, grade, cross slope),• roughness,• texture, and more.
Truck seat vibration vs road roughnessTruck seat vibration intensity @ 75 km/h: RMS(ax,y,z) = 0.18 + 0.30 * IRIZero vibration (0 m/s2) during 100 min loading & pauses.Maximum road roughness for 380 driving min / day, without exceeding the Action Value A(8) = 0.5 m/s2: IRI < 1.27 mm/m, a challenge on low volume roads!Recommended minimum short-term action:Seek to eliminate local road damage causing IRI20m higher than 3 mm/m, as well as steps at road/bridge joints and potholes causing Megatexture1m over 0.60 mm.
Quasi-static lateral forces:-Too sharp curves with insufficient outer banking
Side friction demand is used when designing curve superelevation ν2 ≈ tan(α ) + f s R*g [Swedish Vägverket, VGU] [Norwegian Statens Vegvesen, Håndbok 111] [UK Design Manual for Road s and Bridges ]Side friction demand can also be used as a control measure for instability risk in existing curves, using measured data on curvature and cross slope!
Example side friction demand in a fatal rural curve 5 crashes within 45 m, 2 of them were fatal Excessive friction demandPitfall: Many road design codes use too high side friction supply factors, overseeing the higher side friction need of long vehicles driven with large slip angles.
Transient lateral forces on roads without a strong shoulder:-Deformed pavement edge, due to insufficient lateral support
Rut Bottom Cross Slope Variance -predicting truck roll and lateral buffeting Cause to Rd 331, Ramsele - Ärtrik Variance of Truck Cab Roll Angle vs Variance of Cross Slope difference at HS Åkerö edge damage at 125 275 m 1,2 HS Åkerö 1,0 seen on next 0,8 Variance slide 0,6 0,4 0,2 0,0 126400 126200 126000 125800 125600 125400 125200 125000 RDB distance [m] Variance of truck cab roll angle Pavement RBCSVPhoto: Max Risberg Read the paper for details on RBCSV calculation, draft limit and correlation with hazardous sites.
3D laserscan at HS Åkerö Note: Exploded truck tire A 69 mm deep deformation
Insufficient drainage gradient (DG) -Hot spots located at entrance/exit of banked outercurves. i Right hand traffic Left hand trafficE DG = √ ( i 2 + E 2)DG being lower than 0.5 % is one of the key causal factors behind the fact that outer curves show 5 times higher rate in fatal crashes!
Many new road construction projects has a built-in skid risk: - Insufficent drainage gradient Rd 90, Rödsta - Näsåker Skid risk: If the Drainage Gradient doesn´t exceed 0.5 %, water pools will be formed 6,0 3,0 5,0 2,0 Curvature = 1000 / Radius [m] 4,0 1,0 Gradient [%] 3,0 0,0 2,0 -1,0 1,0 -2,0 Photo: High Coast Rescue Dept 0,0 -3,0 0 2000 4000 6000 8000 10000 12000 Distance [m] Drainage Gradient Unacceptably low Drainage Gradient Curvature12 risk sections with DG lower than 0.5 % in a 12 km long new road.All risk sections located at entrance/exit of banked outercurve.
Curve with 5 crashes within 2 weeks?!?Improper asphalt patching gave extreme crash outcome when raining just after the road work. [Photo: Bengt Andersson]
Patch with low texture gave severe Split-friction Rv 61, Åmotfors - Kristinehamn Vägbanans makrotextur (ytskrovlighet) Avgörande för våtfriktion samt hastighetsberoende del av friktionen Olycksplats 10/9 vid distans ca 4680 m (- upp till ca 200 m) 3,0 2,5 2,0 Textur [mm] 1,5 1,0 0,5 0,0 4300 4350 4400 4450 4500 4550 4600 4650 4700 Distans [m] MPD Vänster MPD Mitt MPD HögerA 66 m long ”fat” patch in the near roadside wheelpath.Patch texture far below intervention level ”Minimum 0.6 mm”.This equals having slick worn tires on one side of the vehicle.
Summarizing the paperNVF statement on the need of actions to mitigate disproportional health and safety risk.Roadex III project case study on the Beaver Road 331.Identifying road features decisive for risk factor such as:• Ride vibration and shock,• lateral force,• poor road surface drainage, and• low friction; often in combo with split friction.Analysis based on available data from road profilers.