Meta-analysis of the difference in accident risk between long and short truck configurations

To investigate whether there is a difference in accident risk for differently sized truck configurations, a meta-analysis was undertaken of all available research. It was found that most studies had been made in the US, and that several methodological problems have plagued this area of investigation, mainly the lack of good exposure data. As larger trucks tend to drive on bigger, and therefore safer, roads, this needs to be taken into account. Some researchers have also suspected that there are systematic differences between drivers of different trucks, but the present analysis showed that this is probably a weak effect. Furthermore, it has been shown that the effects of accidents increase with increasing weight, at least up to a certain point, which makes the comparisons of accident risk sensitive to what type of accident has been investigated. Mean values of the risk ratios between long and short truck configurations were calculated from more than 20 studies, in the categories All, Injuries and Fatal. Also, separate values were computed for studies that had held the influence of road type constant in some way, and those that had not. Given that larger trucks replace a higher number of smaller ones on the roads, the differences in all categories of accidents would seem to indicate that, as a population, heavier trucks have fewer accidents, although the difference is small for Fatal. Unexpectedly, this positive traffic safety effect was more pronounced for the studies that had held road type constant. Furthermore, it was evident from the literature that although the overall effects were positive regarding truck size, larger vehicles have specific problems, which probably put them more at risk in certain environments, like towns.