Understanding Factors Affecting Safety Effects of Indirect Driveway Left-Turn Treatments

Abstract

This article summarizes research that evaluates the effects of various contributing factors on the safety effects of an important indirect driveway left-turn treatment: using U-turns as alternatives to direct left turns from driveways. Crash data were collected at 140 roadway segments where U-turns are used as alternatives to replace direct left turns from driveways, and 32 three-leg unsignalized intersections where direct left turns from driveways are permitted. It was found that U-turn crashes only account for a very small percentage of crashes related with right turns followed by U-turns (RTUT). U-turn crashes occur very infrequently at median openings and signalized intersections. The majority of crashes related with RTUT occur at the section between driveways and downstream U-turn locations. A crash prediction model was developed to identify the factors that contribute to the crashes related with RTUT at weaving sections (the segments between driveways and downstream U-turn locations). The model shows that the major street average daily traffic (ADT), the location of U-turn bay, and the separation distances between driveway exits and downstream U-turn locations significantly impact the safety of RTUT at weaving sections.