Analytical formulation and empirical evaluation of pre-signals for bus priority

• Investigate using additional signals (pre-signals) for bus priority.
• Develop analytical models for estimating delay due to pre-signals.
• Validate analytical models for pre-signals with empirical data.
• Prove that pre-signals can benefit the system for a broad range of situations.

One of the major causes of bus delays in urban environments are signalized intersections. A commonly used solution to give priority to buses at signalized intersections is to dedicate a lane for bus-use only. However this strategy can waste valuable green time at signals and impose additional delays to cars, especially when bus flows are low. Overall, the total person hours of delays in the system (i.e., buses and cars) can increase due to excessive delays experienced by car users. To this end, an additional signal upstream of the main signal, called a pre-signal, can be used to better utilize the capacity of the main signal while still providing bus priority to reduce the system-wide person hours of delays.The aim of this research is to analytically quantify and empirically evaluate the delays encountered by cars and buses with the use of pre-signals. The ultimate goal is to provide domains of applications for the proposed strategy. The paper presents analytical formulations to compute bus and car delays using queuing theory. The analytical models show that for a wide range of cases pre-signals can minimize the system-wide person hours of delays, as compared to dedicating a lane for bus-use only or operating buses and cars completely mixed. The analytical model is validated with empirical data collected at an existing pre-signal, which shows that the delay predictions of the model closely follow reality.