Operational Evaluation of a Compact 120 m Median U-Turn Offset: A Microsimulation Case Study of an Existing Urban Corridor

As rapidly urbanizing cities face increasing car dependency, traditional intersections often reach saturation, necessitating unconventional geometric interventions. This study evaluates the operational efficiency of an unsignalized Median U-Turn (MUT) configuration, specifically investigating the impact of imbalanced offset distances on a high-volume urban corridor in Riyadh, Saudi Arabia. The research evaluates a compact 120 m crossover representing the lower bound of AASHTO recommendations against a conventional imbalanced configuration featuring offsets of 864 m for the Northbound approach and 1.37 km for the Southbound approach. Utilizing PTV Vissim microscopic simulation under a peak demand of 2,415 veh/hr, the methodology analyzes movement-specific dynamics through a 600 second analysis interval scaled to hourly performance. Findings demonstrate that the unsignalized MUT configuration with an imbalanced 120 m offset provides satisfactory operational performance, achieving a system-wide average delay of only 11.11 seconds per vehicle (LOS A). Critically, despite the high Southbound demand of 1,119 veh/hr, the maximum observed queue of 26.63 m utilized only 22.2% of the available 120 m storage length. These results empirically suggest that extreme distances of 864 m and 1.37 km are operationally redundant for this corridor. Implementing the compact 120 m MUT design reduces the additional travel distance for U-turning vehicles by up to 2.4 km per trip by replacing the existing long crossover configuration. The simulation results demonstrate that the proposed 120 m MUT operates efficiently under the observed traffic demand, providing evidence that a compact offset is operationally feasible while improving land-use efficiency without compromising operational stability.