Evaluating the Operational Performance of St. Augustine U-turn Interchange (SUTI)

Abstract

This study evaluates the operational performance of a novel median U-turn interchange—St. Augustine U-turn interchange (SUTI)—as an alternative to a conventional median U-turn on arterial interchange (MUTAI) and four other existing service interchanges. The research integrates two analytical stages: Critical Lane Volume (CLV) analysis using the Highway Capacity Manual (7th Edition), and microsimulation analysis using PTV VISSIM with travel time and maximum queue lengths as the primary measures of effectiveness (MOEs). The simulation is conducted over ten random seeds per scenario to assess all the interchanges under various traffic demands, turning movement proportions, and traffic distributions. The results indicate that the new SUTI interchange required the lowest average cycle lengths to achieve the lowest volume-to-capacity (v/c) ratios, the second-best mean travel times, and the shortest mean maximum queue lengths across various demand scenarios. The conflict-point analysis revealed a reduction in conflict points when compared with conventional diamond interchanges. Overall, the SUTI and diverging diamond (DDI) interchange showed similar results. The new median U-turn design of the SUTI interchange demonstrates a significant improvement in travel time compared to the conventional MUTAI interchange.