An analytical approach to real-time bus signal priority system for isolated intersections

Abstract

Bus signal priority (BSP) is an active traffic management measure to reduce bus travel delay at signalized intersections and to improve the bus service reliability. In this paper, we present a real-time BSP system with a primary focus on its practical implementation. We tackle two inter-related issues of existing priority systems, namely, real-time computation and solution optimality, using an analytical approach. The core of the proposed priority system involves two signal controller actions – red truncation (RT) and green extension (GE), which determine the priority timings based on the objective of minimizing total person delay incurring at the subject intersection. We demonstrate the analytical approach by deriving closed-form expressions for optimal RT and GE for a two-phase signal using cumulative count curves. The inputs required for these priority models are based on average traffic and bus conditions limited to the current signal cycle alone. Solutions for the RT and GE models indicate that three dimensionless variables – ratio of bus-arrival time to traffic queuing time, ratio of bus passenger occupancy to other vehicles’ average passenger occupancy, and ratio of traffic demand to saturation flow ratio – govern the priority decisions. Simulation results showed significant delay reduction for buses (≈22%) with a negligible impact on other traffic users during low to medium traffic conditions and high bus frequencies (3 min headway).

Keywords:

• Green extension
• person delay minimization
• real-time bus signal priority
• red truncation

Acknowledgments

We thank Abhishek Damera, a former student at the Indian Institute of Technology Madras, India for his partial contribution with the green extension formulation. We also thank the Ministry of Electronics and Information Technology (MeitY), Govt. of India for supporting this research through the project ‘InTranSE-II – Development of a bus priority system at signalized intersections using V2I communication’. Finally, we thank the three anonymous reviewers for their comments that greatly enhanced the quality of this paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).