Safety Evaluation for Turnarounds at Diamond Interchanges: Assessing the Texas U-Turn

Abstract

Texas frontage road turnarounds at diamond interchange locations are a common treatment in the State of Texas. This configuration, also often referred to as the Texas U-turn, allows vehicles traveling on a one-way frontage road to access the opposing direction one-way frontage road via a U-turn before the terminal intersections at the diamond interchange. This technique removes two potential left-turn maneuvers from the adjacent at-grade intersections. The frontage road turnaround has operational benefits that result from shifting vehicles that would typically be occupying the intersection. The safety of these turnaround configurations, however, is not well known. This paper focuses on the observed safety performance of these turnaround configurations at diamond freeway interchanges in Texas. The authors first developed a large randomly sampled data set to facilitate a statistically reliable assessment of U-turn safety performance for Texas interchanges. Next they conducted a safety performance assessment at locations with and without turnarounds and determined that site features that significantly influence the number of crashes include the volume of cross street traffic, the cross street right-turn configuration at frontage roads, the minimum radius in the turnaround, the longitudinal distance from the U-turn exit to the closest downstream driveway, and the number of lanes on each frontage road. The safety performance findings at locations with and without turnarounds suggests that an agency could construct a turnaround to enhance facility operations with the knowledge that construction will not adversely impact safety. Although the research introduced in this paper focuses on Texas locations, the findings should be applicable to similar facilities in other states if the turnaround conditions are similar.