Empirical Findings of Bus Bunching Distributions and Attributes Using Archived AVL/APC Bus Data

Bus bunching takes place when headways between buses are irregular leading to longer waiting times for riders, overcrowding in some buses, and an overall decrease on the level of service and capacity. This paper presents a method to identify and visualize bus bunching events temporally and spatially, and an additional method to identify the potential causes and consequences of bus bunching. Sensitivity analyses are performed to compare results across different threshold sets. This research is based on a half-year's worth of data for TriMet's Route 15. TriMet is the transit provider for the Portland, Oregon metropolitan region. Temporal and spatial distributions of bus bunching events indicate high concentration during high frequency service, and increasing concentration toward downstream. Causes and consequences analyses indicate bus bunching due to at-stop variation more than between-stops variation. A switch from schedule-based control strategy to headway-based control strategy during high frequency service is suggested.