Performance Analysis of Parallel Flow Intersection and Displaced Left-Turn Intersection Designs

Abstract

The displaced left-turn (DLT) design, also known as the continuous flow intersection, has proved to be a superior alternative to the conventional intersection in terms of handling heavy volumes during peak periods. In locations where the availability of additional right-of-way and driveway access is not a major concern, the DLT design is a cost-effective and time-saving option compared with the expensive option of grade-separated interchanges. Recently, a new nontraditional intersection design called the parallel flow intersection (PFI) has been proposed. The PFI is also an at-grade design and operates with the same number of signal phases as a DLT. This research compares the operational performance of DLT and PFI designs based on the maximum through and left-turn movement throughputs for three different high-volume scenarios using traffic simulation. The results indicate that maximum throughput values of through movement in the PFI were very close to the values obtained for the DLT. The designs produced similar results, mainly because both operate as two-phase signals (at the main intersection) with equal green times for through movements. The left-turn movement throughputs in the PFI were found to be lower than those in the DLT. For two study cases, the DLT was able to process 180 and 80 more vehicles per hour per lane than the PFI. This is attributable to left-turning vehicles experiencing a greater number of stops, on average, in a PFI than they would in a DLT.