Cost-effective approach to improve median safety on Pennsylvania interstates

Each year nearly 40,000 motorists die and another 3 million are injured in highway-related crashes. The majority of these occurrences are due to driver error. Associated with the many casualties resulting from transportation crashes are enormous societal and economic costs. This research considered both accident prediction modeling and cost-effectiveness evaluations for divided Interstate highways in Pennsylvania.; Research is performed to investigate the appropriateness of the Pennsylvania Department of Transportation median barrier warrants for limited-access, high-speed Interstate highways. Various databases were merged to evaluate both cross-median crashes and collisions with longitudinal median barrier using both Poisson and negative binomial regression. Crash frequency is modeled as a function of geometric and traffic operational variables. Crash severity models were developed using logistic regression with geometric and environmental variables used as predictors. The results of the statistical modeling effort are used to perform a cost-effectiveness evaluation of median safety.; The results of the research show that cross-median collisions are more severe than median barrier crashes. Also, median-related crash frequency models best fit the negative binomial distribution; however, the Poisson distribution also provides an adequate fit to median barrier crash frequency data only. The results of the crash severity modeling suggest that an unordered response for median barrier crash severity is appropriate.; The crash frequency and severity models were used to develop the expected number of fatal, injury, and property-damage only crashes that occur annually on Pennsylvania Interstates. An economic evaluation, using benefit-cost analysis, shows that median barrier should be placed on earth-divided sections of Interstate highway with median widths up to 70 feet wide, and with directional average daily traffic volumes greater than 20,000 vehicles per day, when longitudinal barrier is located at the center of the median. When the barrier is located closer to the traveled way (e.g., 4-feet from left edge), the benefit-cost ratio is reduced. In such situations, benefits outweigh the costs for sections with median widths between 30 and 70 feet and for directional traffic volumes between 20,000 and 50,000 vehicles per day.