Effect of Different Median Barriers on Traffic Speed

Abstract

This study assesses the impact of the types of median barriers installed on the comfort speed of drivers traveling in the median lane. Current guidelines and practices in most jurisdictions across the world assume that the types of barriers used do not have any impact on drivers' choice of speed. However, anecdotal evidence suggests that different drivers react differently to the presence of different types of median barriers due to differences in risk perceptions. If drivers do adapt their behaviors according to the types of barriers installed, then this relationship should be explicitly considered in the selection criteria. A speed study was therefore undertaken at selected sites with different median barriers such as ditch, curb, w-beam, thrie-beam, F-barrier, and F-barrier with chain-link fence. Also, sites were selected in both 70km/h and 80km/h posted speed zones to determine if effects would be consistent across different speeds. By comparing the mean speeds obtained at the barrier sites to those at non barrier sites, consistent differences in comfort speed were found for both speed zones considered. Discussion of implication to road safety and capacity is discussed and some recommendations on future barrier selection are provided.