Crash Modification Factors for Road Diets in Virginia

A “road diet” is a technique that reconfigures the roadway by reducing the number of lanes in hopes of achieving traffic calming and improving safety. Common road diets involve changing a roadway from a four-lane undivided roadway to a three-lane roadway with a center two-way turn lane. This study aims to evaluate the safety effectiveness of road diets in Virginia using the empirical Bayes method and focusing on the common cross sections of AAAA to BATAB and AAAA to BuATABu (A = automobile/general purpose travel lane, B = standard bicycle lane, Bu = buffered or separated bicycle lane, and T = one-way or two-way left-turn lane). A total of 40 sites were identified in 15 Virginia cities. A crash modification factor (CMF) of 0.65 is recommended for total segment crashes and a CMF of 0.41 is recommended for fatal and injury (FI) crashes. The standard errors for both these CMFs are 0.125 and 0.154, respectively, and both CMFs were found to be statistically significant at a 95% confidence level. Further research and data collection are needed to expand this work for other roadway cross sections as well as development of intersection CMFs. Based on the computed results, it is concluded that road diets can potentially reduce crashes and public agencies should consider the benefits of road diets in both safety and mobility when justifying roadway improvements.