Cross-Median Collisions on Pennsylvania Interstates and Expressways

Abstract

Cross-median collisions (CMCs) on high functional class roadways are a concern because of the potential economic and social losses that often accompany these crashes. The Pennsylvania Department of Transportation (PENNDOT) design policy suggests protecting medians on divided highways where the median width is less than 10m (32.8 ft) and the average daily traffic is above 20,000 vehicles per day. However, CMC crashes have occurred where a barrier was not warranted by the policy. The methodology used to assess median safety on Interstates and expressways in Pennsylvania is reviewed, and the findings are reported. A critical review of literature and an assessment of various state department of transportation median safety practices were undertaken. An expert panel qualitatively assessed median safety practices and provided input for quantitative data collection. Two PENNDOT databases, police accident reports, photologs, and field data were analyzed to complement the qualitative findings. Qualitative results suggest that the three-strand cable system, strong-post W-beam guiderail, or the concrete safety shape are recommended median barriers in appropriate site conditions. Quantitative results show that CMC crashes are rare events; however, nearly 15% involve fatalities and 72% involve nonfatal injuries. In addition, CMC crash rates at earth-divided highways decrease as the median width increases, CMC crashes appear more likely to occur downstream of interchange entrance ramps, and CMC crashes are more likely to involve adverse pavement surface conditions (wet or icy) than are other crashes. Negative binomial regression models were used to model CMC crash frequencies on earth-divided highways.