Comparison of Operations of Single-Point and Tight Urban Diamond Interchanges

Single-point urban interchanges (SPUIs) and tight urban diamond interchanges (TUDIs) are alternatives typically considered in locations where roadway right-of-way is constrained. The body of research comparing these two interchange types is limited, and operational comparisons are varied in their findings. It is believed that the traffic operation performance of these two interchange types does not differ significantly, which makes it challenging for transportation practitioners to select a preferred interchange type for a specific location. The operations of the geometrically similar SPUIs and TUDIs were compared using microscopic simulation analysis for a wide range of volume conditions. The analysis was conducted with CORSIM using optimum signal phasing and timing for both interchange types. Three specific test volume cases and five varying volume levels were developed for both interchange types to evaluate the interchanges over a range of capacity conditions. The 30 cases were analyzed using microscopic simulation, and results were summarized to compare the two interchange types. The findings show that for the geometric and volume conditions tested, the SPUI provides greater traffic operation performance than the TUDI. Over the range of tests, the SPUI provided higher average travel speeds, fewer phase failures, a lower percentage of stops, and a considerably higher capability to serve traffic. The results typically show that the TUDI will reach capacity conditions when the SPUI is operating at average conditions.