A Study of Headway Maintenance for Bus Routes: Causes and Effects of "Bus Bunching" in Extensive and Congested Service Areas

A healthy and efficient public transit system is indispensable to reduce congestion, emissions, energy consumption, and car dependency in urban areas. However, some bus routes chronically underperform. Research on travel data suggest the compactness of the urban area and network may have a significant influence on the efficiency of transit services and the mode shares of transit and walking (Pucher and Renne, 2003). Dispersed suburban areas and low densities negatively affect costs and service levels. In addition, uncertain travel times and passenger demand preclude schedule adherence and headway uniformity. In a stochastic environment, deviations from schedules are unavoidable and…

A healthy and efficient public transit system is indispensable to reduce congestion, emissions, energy consumption, and car dependency in urban areas. However, some bus routes chronically underperform. Research on travel data suggest the compactness of the urban area and network may have a significant influence on the efficiency of transit services and the mode shares of transit and walking (Pucher and Renne, 2003). Dispersed suburban areas and low densities negatively affect costs and service levels. In addition, uncertain travel times and passenger demand preclude schedule adherence and headway uniformity. In a stochastic environment, deviations from schedules are unavoidable and “bus bunchingâ€Â takes place when headways between buses are irregular leading to longer waiting times for riders, overcrowding in some buses, low number of passengers in the remainder buses, and an overall decrease on level of service and capacity. This study will focus on TriMet, the transit operator in the Portland metropolitan region, routes that experience difficulties in terms of schedule adherence and on time performance. These routes, denoted route 15 and route 72, are characterized by their long distance and their high buffer to absorb uncertainties. As TriMet is implementing a new state-of-the-art communication and bus dispatching system in 2010-2011, the main goals of this proposal are to: (a) provide a before and after study of the dispatching system performance using routes 15 and 72 as a case study, (b) understand the causes and effects of bus bunching, (c) study the tradeoffs between schedule adherence, route length, and headway regularity, (d) propose new control strategies that can be implemented with the new dispatching and communication system, and (e) explore the use of bus location visualization techniques to help understand the bus bunching problem. The combination of advance statistical analysis, mathematical modeling, and visualization is an innovative approach to the research of transit operations. Recommendations for the new system architecture will be provided based on the data needs and opportunities identified in the course of this research.