The complex relationship between increases to speed limits and traffic fatalities: Evidence from a meta-analysis

Speed plays an important role in road safety as it affects accident risk and severity. Among safety policies implemented to control driving speed, speed limits are the most highly developed. Since the 1970's, numerous studies have focused on the effectiveness of speed limits, but even today there is still no clear consensus as to the impact that raising the speed limit has on traffic fatalities. With the aim of consolidating knowledge on this topic, a meta-analysis has been carried out of a set of econometric studies assessing the effects on traffic fatalities of increasing speed limits in the US. Two sub-samples were obtained, taken from the traffic fatality measures considered by studies (fatality count and fatality rate normalized per vehicle miles traveled), and two approaches were analyzed: rural interstates (where speed limits were increased in 1987 and 1995), and a statewide approach (all roads network). Our findings show that by count traffic fatalities went up on both rural interstates and statewide level, although the effect was higher on rural interstates. In other respects, statewide fatality rates could be improved in relative terms by raising legal speed limits, although the effect would be weak.