Research Papers (2009 – 2013)

Abstract

Directional mid block median openings with left-turn lanes and loons between four-leg signalized intersections without median openings are designed to smooth the flow of traffic, especially on main streets. In recent years, there has been growing interest in their potential benefits as they raise the mental capacity of drivers by increasing the flow and reducing the delay caused by traffic signals. This interest has created a need for collecting data regarding the safety effect of U-Turns. The safety effect of converting signalized intersections in Tehran to u- turn with directional mid block medians was estimated by a preliminary analysis. It removes through movements in minor roadways as well as all left turns from both major and minor roadways. Using crash and traffic volume data for a comparison group, regression models were computed to represent the safety performance of signalized intersections by crash frequency as a function of traffic volume. An empirical Bayesian procedure was used to estimate what would the expected number of crashes at the converted intersections have been had they not been converted. The empirical Bayesian estimates were compared with actual counts of crashes after the conversion. Aggregate results indicated that after replacing signals with U-Turns, there was an increase of approximately 13.57 % in crashes.

Abdolreza Shikholeslami and Leila Azizi