This study investigates the relationship between speed-limit increases and increases in the number of fatal crashes on U.S. rural and urban interstates. Past studies use expected historical trends to support claims that “speed kills.” Using structural modelling, we assess the change in the average of the time series after a known change in speed limit occurs. The analysis is carried out separately for urban and rural interstates for each state. The results cast doubt on the blanket claim that higher speed limits and higher fatalities are directly related. After the initial speed-limit increases in 1987, the number of fatal accidents on rural interstates increased in some states but not in all. The 1995 round of speed-limit increases generally showed smaller increases in fatalities on rural interstates and slight to no increase on urban interstates. The approach also allows identification of seasonal effects that vary across the states. (Author/publisher)
Abstract