Evaluation of transit signal priority and optimal signal timing plans in transit and traffic operations

Transit signal priority (TSP) systems have been in place for several years. Traffic simulation models are frequently applied to evaluate the benefits of such treatments before implementation. These benefits can take several forms, including reduced travel time for transit customers, improved schedule adherence, and reduced operating costs for the transit provider. This paper reports a case study that highlighted and embodied the following issues: (a) if signal timing is optimized, the TSP may provide only incremental benefits and not be a cost-effective investment; (b) if signal plans are not updated as often as needed, TSP may provide a way of adapting the base signalization, providing much of the benefit of signal plan updates; (c) side-street traffic does not always suffer because of TSP, nor does main-street nonbus traffic; (d) some critical intersections, with heavy competing volumes, may need to be dropped from the TSP plan to have no excessive adverse impact on the cross street, which may itself be an arterial; and (e) bus travel time reductions can result in fewer buses needed to serve the demand at the same level of service and thus reduce bus transit operating costs. Simulation was an important and cost-effective tool in this case study.