Sensitivity Analysis of Transit Signal Priority Impacts on Operation of a Signalized Intersection

Abstract

The study consists of a systematic simulation evaluation of transit signal priority (TSP) impacts on the operations of a single signalized intersection within a coordinated arterial system. The study demonstrates first that in general TSP provides benefits to transit vehicles that receive priority. Second, TSP has a marginal systemwide impact for low traffic demand, although as the demand increases, so do the systemwide disbenefits of TSP. Third, the systemwide impact of TSP is directly proportional to the frequency of transit vehicles. Fourth, TSP impacts are sensitive to the demand distribution at a signalized intersection. Specifically, transit vehicle arrivals on heavily congested approaches may result in systemwide benefits if the conflicting approaches are not congested. Alternatively, transit vehicle arrivals on lightly congested approaches may produce significant systemwide disbenefits if the conflicting approaches are heavily congested. Fifth, the systemwide benefits of TSP are dependent on the phase at which the transit vehicles arrive, especially if the cycle length is maintained within the priority logic. Sixth, the systemwide benefits of TSP are highly dependent on the optimality of the base signal timings. Finally, transit vehicle dwell times at nearside bus stops can have significant systemwide impacts on the potential benefits of TSP.