Safety Analysis of Constructed U-turns in the City of Tehran

Directional midblock median openings with Left-Turn Lanes and Loons between four-leg signalized intersections without median openings are designed to smooth flow of traffic especially on main streets. In recent years, there has been growing interest in their potential benefits as raising mental capacity of drivers by increasing the flow and reducing the delay caused by traffic signals. This interest has developed a need for data on safety effect of U-Turns. In this paper, the safety effect on u-turns crashes of converting signalized intersections in Tehran from traffic signal removal to install directional midblock median was estimated. The six such conversions were studied in this research. Safety analysis of u-turns conversions was done by modeling of U-turns crashes by statistical methods. Accident prediction models for crash types and crash frequency were developed to examine the geometry and traffic factors contributed to the crashes at u-turns conversions. The data analysis results show that a 10% increase in separation distance (weaving length), external radius and median opening length will result in a 2.36%, 37.6% and 12.6% decrease in angle crashes, respectively. Also, a 10% increase in roadway width will result in a 20% decrease in total crashes. Increasing speed on major roadway, will result increase in rear-end accidents due to large speed differential between u-turn and through vehicles. Therefore speed increase on minor roadways that converges to the major ones, will result in decrease in rear-end crashes. Furthermore, total crashes and crash types are increased with the ADT increase on the major streets and u-turns.