Accidents between pedestrians, bicyclists and motorized vehicles: Accident risk and injury severity

Sammanfattning: The aims of this work are to better understand (1) the relation between exposure and the risk of an accident between pedestrians and motorized vehicles and between bicyclists and motorized vehicles occurring at urban intersections and (2) how the speed environment and the victim´s age relate to the injury severity/outcome once a pedestrian or a bicyclist has been struck by a motorized vehicle. Cross sectional studies are used, and the relations are analyzed using multinomial logit models, negative binomial regression and other statistical methods. The results show that there is a positive correlation between the exposure of pedestrians, bicyclists and motorized vehicles and the number of accidents, i.e. the more road users there are, the more accidents occur. The models also suggest that this relation is non-linear; the accident risk per road user is lower at sites where the exposure is greater (safety in numbers effect). Furthermore, the results show safety in numbers effect for single pedestrian accidents, which might suggest that the underlying reasons for this effect is more complex than previously assumed. The thesis suggest an alternative way to interpret risk values and risk curves for injury severity/outcome (if one is involved in an accident), in which differences arise depending on whether the aim is to interpret the relation from an individual perspective or from the perspective of society as a whole. The results furthermore show a strong correlation between the speed environment, the age of the victim and the injury severity/outcome. A considerable proportion of the serious injuries occurs in low speed environments, seniors suffer more serious injuries than younger pedestrians and cyclists do, and the effects differ substantially for struck pedestrians versus struck bicyclists.