Have They Bunched Yet? An Exploratory Study of the Impacts of Bus Bunching on Dwell and Running Times

If transit agencies wish to retain and attract riders, they need to provide reliable and efficient services. Transit agencies tend to run high-frequency bus routes during peak hours, and in many cases, different routes can also overlap along major corridors. In some instances, consecutive buses can arrive at a shared stop simultaneously or while another bus has been standing at the stop. This phenomenon, known as bus bunching, can delay buses and passengers, and is inefficient. In this study, the authors attempt to understand how bus bunching from the same or different routes can impact bus operations, specifically dwell and running times. This research uses stop-level records obtained from automatic vehicle location (AVL) and automatic passenger counter (APC) systems from TriMet, Portland, OR. Using linear modeling, we find that bus bunching increases both dwell and running times. Specifically, when different routes are scheduled to arrive at a bus stop within a short time frame, dwell times increase more than if buses bunched from the same route. In contrast, bunching from the same route prolongs running times more compared to bunching with buses from different routes. The authors findings suggest that bus schedulers and operators consider adding more time between consecutive buses from different routes at shared stops to minimize the negative impacts that they observed from bus bunching.