Redesigning black spots in traffic: an effect evaluation

Abstract

In order to work to a better traffic safety, many countries handle a black spot program, through which the most dangerous traffic spots are selected and subsequently the infrastructure is adapted. To handle these black spots, a lot of means are invested, but often the outcome for traffic safety remains unclear. Therefore we evaluated the effect of the adaptation of dangerous traffic spots on traffic safety. Through analysis of the crash rates, this study evaluates the safety effects of an extensive black spot program that has been implemented in Flanders-Belgium. This program included around 800 black spots, from which 134 locations, redesigned between 2004 and 2007 were included in this study. The adopted approach is an Empirical Bayes before-and-after study that accounts for effects of general trends and for the stochastic nature of crashes, including regression to the mean. Two different comparison groups were established. Furthermore ANOVA analyses were made to check whether differences in effects occurred depending on the characteristics of the location and the implemented intersection design. Dependent on the applied comparison group, the analyses showed a decrease in the number of injury crashes of 24 to 27%, significant at the 1%-level. A separate analysis for crashes with serious or fatal injuries showed a decrease of 40 to 52%, also significant at the 1%-level. The results suggest a more favourable evolution for intersections that were priority controlled in the before situation compared with signal-controlled intersections. Crash reductions were also higher at locations with a lower traffic volume compared to locations with a higher volume. This study shows the investment of the means in a black spot program does have a favourable outcome on traffic safety. A critical selection of the black spots can help to reach stronger traffic safety effects with less means.