HEADWAY DEVIATION EFFECTS ON BUS PASSENGER LOADS: ANALYSIS OF TRI-MET'S ARCHIVED AVL-APC DATA

Abstract

In this paper we empirically analyze the relationship between transit service headway deviations and passenger loads, using archived data from Tri-Met’s automatic vehicle location and automatic passenger counter systems. The analysis employs two-stage least squares estimation to account for the simultaneous relationship between headway deviations and loads. Controlling for the effects of passenger activity on delay, the results indicate that the observed incidence of excess passenger loads is systematically attributable to deviations from scheduled headways. In turn, analysis of the causes of headway deviations served to identify possible operations control actions that would improve service regularity and, consequently, reduce incidences of overloading and forestall the need for additional service.