Evaluating the cost-effectiveness of roadside culvert treatments

Roadside cross-drainage culverts have been found to affect vehicle accident injury levels. As a result, highway designers have commonly used three safety treatments to protect errant motorists from striking culvert openings. These safety treatments have included: culvert extension, guardrail installation, and the application of safety grating. However, the identification of the most appropriate safety treatment for roadside culverts may be challenging; accident costs may dramatically change under different road and traffic characteristics. The purpose of this study was to estimate accident costs for a wide range of road and traffic scenarios and then define the safest treatment (i.e., treatment with lowest accident cost) for a variety of traffic, roadway, and roadside characteristics. Over 3,000 highway scenarios were modeled using the Roadside Safety Analysis Program (RSAP). This study showed that the selection of culvert safety treatments should be flexible when considering different road and traffic characteristics. The findings demonstrated that culvert extension and grating were found to produce the lowest accident costs for all highway scenarios that were modeled, and guardrail protection was not recommended for any of the scenarios. Therefore, it is believed that the expanded adoption of culvert extension and culvert grates can improve overall highway safety.