Surrogate safety assessment for a tight urban diamond interchange using micro-simulation

This paper presents development of a surrogate safety assessment method and its application to a real-life traffic engineering project. The Tight Urban Diamond Interchange (TUDI) is one of the most commonly used interchange types in the United States. Because of the complex traffic flow patterns, large turning movements and limited spacing between the traffic signals, TUDI is often a source of traffic accidents and bottlenecks. Although U-turns have proven to be beneficial to increase capacity, they also tend to substantially increase traffic conflicts and accidents around the interchange area. Installation of metering-type signals at the U-turn approaches of TUDI has recently been proposed by traffic engineers as a countermeasure to reduce traffic conflicts. In this study, the time-to-collision (TTC) and the post-encroachment-time (PET) are used as the surrogate safety indicators to evaluate the safety level of a TUDI. Several simulation plug-in modules are developed to extract the surrogate safety indicators for safety assessment of installing metering type signals. The results show that although applying a metering signal in U-turn areas will decrease the capacity, it has a positive effect on the intersection safety.