Pre-signals for bus priority: basic guidelines for implementation

Abstract

When compared to cars, public transportation (e.g., buses) can carry more people using less space. Hence, by increasing the share of people traveling by bus within an urban network, we can improve the efficiency of the urban transportation system, ultimately making it more sustainable. Unfortunately, buses operating mixed with cars can often get stuck in car congestion. One commonly used solution is to dedicate a lane for bus-use only. However, when bus flows are low, dedicated lanes running through intersections can reduce the discharge flows from these locations and lead to increased car delays, car queues, and all the negative externalities associated with congestion. This, in turn, can reduce the overall efficiency of the transportation network. Therefore, a solution is to discontinue the dedicated lane upstream of the main signal, removing bus priority at intersections. In this paper, we advocate the use of pre-signals upstream of signalized intersections to continue providing bus priority while minimizing the disruptions to car traffic. Pre-signals can allow buses to jump the car queues upstream of signalized intersections, while allowing cars to utilize the full capacity of the main signal when buses are not present. In this paper we provide practical guidelines on how to implement pre-signals at signalized intersections. Ideas on how to operate pre-signals are provided by using recent analytical and empirical findings from previous research on pre-signals. The reduction of system-wide (buses and cars) person hours of delay by using pre-signals, as compared to mixed-use lanes or dedicated bus lanes is also quantified. By doing so, the domains of application of pre-signals are also defined. This information can then be used to determine where and when pre-signals should be implemented in real urban networks and to quantify their benefits to the system.