The J-turn, also known as RCUT (Restricted Crossing U-Turn) and Superstreet, is an innovative geometric design that can improve intersection safety. Even though this design has been in use in several states for many years, there is very little research-based guidance for several design parameters. A driving simulator study was conducted to analyse the parameters of lane configuration, U-turn spacing, and signage. Two lane configurations were examined: 1) acceleration/deceleration configuration where acceleration and deceleration lanes are provided and 2) deceleration only configuration where only deceleration lanes are provided. Lane configuration was found to be the most important parameter affecting J-turn safety based on speed-differentials. The only significant interaction effect among parameters was between lane configuration and U-turn spacing. The acceleration/deceleration configuration performed better than the deceleration only configuration with 66.3% fewer safety critical events. Vehicle trajectories and average lane change locations showed that U-turn spacing impacted significantly the acceleration/deceleration configuration (e.g. average merge locations changed by 96% to 101%) but not the deceleration only configuration. No strong preference was demonstrated by the study subjects for either the directional or the diagrammatic signage style. This report presented the first human factors study of the J-turn focused on developing design guidance. This human factors approach complements other traditional approaches such as crash analysis and micro-simulation. (Author/publisher)
Abstract