Guidelines for the Use of Some Unconventional Intersection Designs

Several unconventional intersection schemes have been proposed to improve the performance of intersections with heavy left-turn movements. These unconventional schemes were shown to outperform conventional intersections under moderate- and high-volume conditions or in the existence of extremely heavy left-turn movements. However, guidelines for the implementation of these intersections have not been extensively discussed. Little research has been done comparing the performance of these intersections under different flow conditions. This study evaluates and compares the operational performance of four unconventional intersection schemes: the Crossover Displaced Left-Turn (XDL), the Upstream Signalized Crossover (USC), the Half USC, and the Median U-turn (MUT) design. The paper discusses signal optimization strategies for the intersections and identifies the important operation issues. The micro-simulation software VISSIM was used to model and analyze the four unconventional intersections as well as a conventional one. Intersection average control delay was used as a Measure of Effectiveness (MOE) to compare the performance of different designs. Based on the analysis, guidelines for the implementation of each design under various traffic volume scenarios are presented.