Heavy truckers out of control

Writing in the International Journal of Vehicle Safety, the researchers explain that negotiating a bend is the main cause of loss of control, closely followed by avoidance manoeuvres, and road-edge recovery.

Sogol Kharrazi and Robert Thomson of the Department of Applied Mechanics, at Chalmers University of Technology, Gothenburg, Sweden have analysed data from the Large Truck Crash Causation Study database and looked at what caused the drivers to lose control of their vehicles. They considered accident type, what kind of manoeuvres preceded the accident, the class of vehicles involved in the accident, driving conditions and road characteristics.

By identifying common critical manoeuvres the team hopes, not only to educate the trucking industry but also to inform those involved in truck design and manufacture and road building about the factors that lead to the most accidents involving heavy trucks. Their study did not take into consideration accidents involving trucks in which the truck was not the cause or where driver fatigue, inattention or vehicle failure was involved.

Overall, they explain, loss of control was associated with almost a fifth of trucks involved in accidents. Turnover was a more common type of loss of control than yaw instability, skidding or jack-knifing, with more than half of trucks that underwent loss of control rolling whereas less than a third involved simply severe deviation from the intended path due to under-steer, over-steer, or trailer swing. About 14% experienced both yaw instability and turnover. Most (84%) of loss of control accidents involved a single vehicle.

Negotiating a bend in the road was the main critical manoeuvre leading to loss of control, with almost two-thirds of incidents taking place on a curve, the researchers say. Avoidance manoeuvres accounted for more than one in ten of loss of control accidents and similar numbers where the driver was attempting to regain position on the road after veering off into a verge.

Intriguingly, wet conditions were not a common factor in loss of control accidents. Dry road conditions were present for three quarters of all trucks which underwent loss of control, the researchers report. However, wet road conditions were associated with more than half of trucks that jack-knifed or otherwise underwent yaw instability.

Turning at intersection, lane change, heavy braking on straight roads, collisions with pedestrians or animals, or speeding on low-friction straight roads also accounted for a small percentage of loss of control accidents, the researchers add. For the heavy braking accidents, trucks involved often had no Antilock Braking System installed.