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Safety Impacts of Directional Median Openings at Downstream U-turn Locations

Over the past decades, many states and local transportation agencies have installed directional median openings on urban divided roadways to help avoid potential conflicts. At directional median openings, left-turn movements from driveways or minor streets have to make an alternative movement, i.e., a right-turn followed by a U-turn, which would increase the U-turn demands at the downstream openings and may increase the crash risk at the U-turn locations. Therefore, the objective of this study was to investigate the safety impacts of directional median openings at downstream U-turn locations. For this purpose, a Poisson regression model was developed to analyze the factors that contributed to the crashes that occurred at the downstream U-turn locations of directional median openings. The results showed that 1) higher downstream U-turn volume and left-turn volume resulted in more crashes at downstream U-turn locations and 2) the closer the downstream U-turn location was to the subject opening, the more crashes that occurred at the downstream U-turn location. These findings indicated that the selection of U-turn locations is critical for the safety performance of directional openings because converting a full median opening to a directional median opening generates more U-turns at downstream openings. Diverted left-turn traffic should not be allowed to make U-turns at a closely-spaced opening that already has significant U-turn or left-turn volumes.