Correlation between truck combination length and injury risk

Literature studies show that it is a very complex task to estimate how traffic safety is affectedby the introduction of longer truck combinations. Some studies indicate a slightly increased risk of crashes per vehicle kilometre and that the change in risk depends on the vehicle combination. Other studies show that the difference in crash risk in comparison to conventional heavy goods vehicles is small, at least for trucks travelling on larger roads. In the current study, the effect of increased vehicle combination length on the rates of fatal or severe injury crashes by vehicle kilometres travelled is investigated. The method uses Swedish national crash data fr om the period 2003 to 2012. Unlike most other countries in the European Union where an upper limit of 18.75 metr es is in force, vehicle combinations up to 25.25m are permitted in Sweden. The aim is therefore to determine whether “long” truck combinations (with a combination length of 18.76 – 25.25m) have a higher associated rate of severe or fatal crashes by vehicle kilometres travelled than “medium” (12.01 – 18.75m) or “short” combinations (less than 12m). Different approaches for comparing the number of fatal or severe crashes in the three length groups with the kilometres driven are discussed. The crash type distributions in the three length groups are compared and it is considered to what extent the observed differences can be explained by differences in the exposure data.