, Professor, Civil, Environmental and Geo-Engineering
A cross-median crash occurs when a vehicle leaves its traveled way, completely crosses the median dividing the highway's directional lanes, and collides with a vehicle traveling in the opposite direction. AASHTO's Roadside Design Guide recognizes two countermeasures for prevention of cross-median crashes: 1) medians wide enough to provide adequate "clear zones" in which a driver can stop or regain control of the vehicle before crossing into the opposing traffic stream, and 2) installation of median barriers when medians are less than 10 meters wide and annual daily traffic is greater than 20,000 vehicles/day. As with any safety countermeasure, installation should begin with those locations showing the greatest expected benefits. This project reviewed the state-of-the-art in median-crossing crash (MCC) protection through a literature review and a survey of current practices. This was followed by statistical modeling of the frequency of median-crossing crashes in Minnesota, with the goal of identifying those locations where countermeasure installation is most likely to pay off. A statistical technique was developed for estimating the frequency and rate of MCCs on each of a set of highway sections, which required the analyst to review only a subset of hard-copy accident reports. This technique was applied to Minnesota's freeways and rural expressways, and highway sections were ranked with respect to estimated frequency of MCCs. An initial version of a simulation model was developed for comparing the cost-effectiveness of barrier projects on different highway sections. The model used Monte Carlo simulation to estimate the probability that an encroaching vehicle crosses a median with a specific cross-section and collides with another vehicle traveling in the opposite direction. The model was implemented as a pair of linked Excel spreadsheets, with a companion macro written in Visual Basic for Applications. Finally, this project investigated method(s) for predicting the crash-reduction benefits of median barrier treatments on particular highway sections.