Effective placement of detectors at diamond interchanges

Abstract

Most signalized interchanges in Texas are tight urban diamond interchanges of freeways having one-way frontage roads. At these interchanges, traffic actuated control with improper location of detectors may result in inefficient traffic operations. Further, the signal designer usually does not have published guidelines on the optimal location of detectors at diamond interchanges based on traffic conditions. Therefore, application guidelines on the placement of detectors at diamond interchanges are needed which would result in efficient traffic operations. This research addressed the problem of determining the effective placement of inductive loop detectors on frontage roads at diamond interchanges to minimize total interchange delay. TEXAS Model for diamond interchanges was used to perform simulation studies to determine the optimal location of loop detectors on the frontage roads of diamond interchanges. "Figure 3 and Figure 4" signal operations were the two phasing strategies considered for study. This research developed a set of detector application guidelines which were shown by TEXAS Model to provide efficient traffic operations. When a 40-foot long stop line detector and a 6-foot long advance detector are used on the frontage roads, it appears that a 100-foot setback distance for the advance detector results in the lowest interchange delay for both "Figure 3 and Figure 4" phasing sequences. The I 00-foot setback distance produces less delay than detector layouts having longer advance detector setback distances. In addition, total interchange delay appears to be very sensitive to increase in U-turn volume for the "Figure 4" phasing sequence.