Road accidents of trailer combinations in Finland: A case study

In the years 1982 - 1986, road accident investigation teams in four counties in Finland made in-depth investigations of 171 accidents involving at least one lorry & trailer or lorry & semitrailer combination. About 1/2 of the accidents were collisions between motor vehicles outside junctions, 1/4 collisions at junctions, 1/7 were single accidents and 1/10 accidents involving pedestrians, cyclists or mopedists. The trailer combination was considered the main quilty party in 39 % of the collisions between motor vehicles. 44 % of the collisions between motor vehicles caused by trailer combinations were rear-end collisions or accidents caused by last-moment manoeuvres to avoid a rear-end collision. 22 % of the single accidents were also of the latter type. These accidents were frequently caused by too close following and too high speed. Driver fatigue was one of the causes in 35 % of the single accidents and 16 % of the collisions were caused by trailer combinations. Defective or ineffective brakes were one of the accident causes in 11 cases. The brakes were sufficiently effective and the brake force distribution between the lorry and the trailer was well balanced only in 1/7 of the trailer combinations involved in the accidents. The time fag from the moment brake pedal was stepped on to the moment wheel brakes began to operate was within satisfactory limits (not more than 0,6 - 0,8 s) in about a third of the trailer combinations. There is, however, no evidence that the bellies of the vehicles involved in accidents were any worse than the brakes of all other such vehicles in traffic. According to the survey, accidents of trailer combinations could be reduced if a) drivers would keep greater distances when following other vehicles, b) drivers would avoid driving underfatique, c) police enforcement of compliance to the driving time regulations were increased, d) driver aspirant selection and education were improved and e) regulations concerning the brakes of trailer combinations were more up-to-date.