Impact of Transit Signal Priority on Level of Service at Signalized Intersections

The assessment of Transit Signal Priority (TSP) impacts at traffic signals is typically based on simulation and field studies. There is a need for macroscopic procedures for analysis of TSP as part of the Highway Capacity Manual (HCM) analysis methodology for signalized intersections. This capability will allow prediction of TSP impacts (and related control strategies) at a planning and operations level without the complexity of simulation modeling. The paper presents a technique of estimating the average green times for each lane group, and modifications to the HCM formula for estimating control delay in order to estimate the impact of TSP on the Level of Service (LOS) at each approach and the whole intersection. The technique uses readily available information on the frequency of the transit vehicles, TSP features (e.g., green extension, or red truncation), and also takes into consideration the additional delays because of the residual queues that are likely to occur on non priority approaches operating close to saturation. Application of the method at a signalized intersection with signal priority in the San Francisco Bay Area, and comparisons with simulated data show that the proposed methodology provides reasonable estimates of the TSP impacts, and it can be incorporated into the HCM analysis procedures for signalized intersections. © 2011 Published by Elsevier Ltd.