Optimization Model for Transit Signal Priority Under Conflicting Priority Requests

Abstract

This study proposed an optimization model to resolve conflicting transit signal priority (TSP) requests. Bus travel delay was selected as the index to measure the priority level of a TSP request. Meanwhile, weighting expressions for priority strategy, transit route level, and transit mode were introduced to this model. Here, requests calling for different priority strategies and coming from different transit route levels and transit modes were granted different levels of importance. This model grants priority to the buses with the largest weighted delay. Vissim and its COM interface were then used to conduct a case study and to demonstrate the performance of the proposed model. Results indicate that the proposed model significantly outperformed the baseline model (no priority), Model 1 (using a first-in, first-service policy), and Model 2 (a typical previous optimization method) in average bus delay and associated impacts on other vehicles and systemwide. More specifically, average bus delay was reduced by more than 20.47% versus the baseline model, 16.52% versus Model 1, and 11.70% versus Model 2; the delay of other vehicles was 4.34%, 12.1%, and 8.69% lower than for the other three models, respectively. Average systemwide delay was improved 4.08%, 15.16%, and 7.28%, respectively, versus the other three models separately. When the proposed model was compared with Models 1 and 2, the benefits to transit vehicles provided by the proposed model increased as traffic demand increased.