Analysis of Bus Bunching Impact on Car Delays at Signalized Intersections

In uncontrolled bus systems, buses tend to bunch due to the stochastic nature of traffic flows and passenger demands at bus stops. It is widely acknowledged that bus bunching affects transit operations increasing passenger waiting times and variability. However, transit systems are a part of urban transportation systems. Accordingly, buses also affect traffic flows at signalized intersections leading to additional car delays. In this paper, the impact of a linear bus stop on cars caused by one bus is analyzed by employing the shockwave theory. Further, the operating characteristics of bus bunching in terms of the dwell time at a linear stop are analyzed, in both passenger self-organization and stop-skipping control strategy scenarios. Then, the total dwell time of two bunched buses is calculated, considering different passengers on the two successive buses and the difference between boarding and alighting passengers. Finally, the proposed car delays model is simulated with the aid of computer, where numerical analysis is done to obtain the difference in car delays between two evenly spaced buses and two bunched buses. The results of the numerical analysis indicate that bunched buses lead to additional car delays compared to evenly spaced buses. In addition, numerical tests are conducted for the self-organization and stop-skipping control strategies considering imbalanced passengers on two successive buses and the difference between boarding and alighting passengers. The results show that larger differences between the numbers of passengers on the two bunched buses and lower differences between the numbers of boarding and alighting passengers lead to larger car delays.