Effects of emergency escape ramps on crash injury severity reduction on mountain freeways: A case study in China

Abstract

Emergency escape ramps (EERs) is an infrastructure of mountain freeways to stop runaway vehicles. As the last defence of vehicle occupants’ safety, the performance of EERs in reducing crash injury severity is a concern for stakeholders of road safety. Based on crash records collected on a mountain freeway equipped with five EERs, this study compared the injury severity of crashes on EERs and other road sections, and identified the factors that significantly influence injury severity in the two conditions. Estimations of the parameter coefficients and marginal effects of a random parameters ordered probit model were used to infer EER performance under the impacts of various factors. The results confirm the effectiveness of EERs on the reduction of crash injury severity. The protection function of EERs is weakened by nighttime, the rollover status of crashed vehicle, multi-vehicle collisions, improper design or installation of the roadside infrastructure, drivers’ unfamiliarity with local driving conditions, and crashed vehicle weight. The paper compares the findings with those of previous studies and proposes some recommendations to improve EER performance for occupant and property protection on mountain freeways.