Median Design Considerations Based on Crash and Cost Analyses

Depressed medians on limited access, divided highways separate opposing traffic and provide a recovery area for errant vehicles that run-off-the-road left of the traveled way. Appropriate median widths are determined based on the potential need for median barrier. The American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide provides median barrier warrant criteria based on median width and average daily traffic volume. These guidelines have remained relatively unchanged since the 1970s. Most state transportation agencies have adopted the AASHTO median design policy as standard practice for all high-speed, limited access, divided Interstates and expressways. Roadway inventory and median-related crash data were collected on limited access, divided highway in several states to evaluate existing median barrier warrant criteria. Analytical results from two separate studies are presented in this paper. Regression models of median-involved crashes were developed and comparative analyses were conducted to assess the adequacy of the existing AASHTO median barrier warrant criteria. Further, cost-effectiveness analyses using Pennsylvania Interstate data are presented. Based on the results of both studies, there is a benefit of installing longitudinal barrier on divided highways with median widths up to 70 ft. These results are based on using the existing design-decision variables of median width and average daily traffic.