Evaluation of Bus Reliability Measures and Development of a New Composite Indicator

Abstract

Reliability is cited as a key aspect of service quality, but many of the indicators in use today do not measure reliability from the user's perspective. A review of earlier work on transit user behavior concluded that the traveler's perspective of reliability was driven by punctuality in arriving at the destination, short waiting times at the origin stop, and consistent wait and travel times. Twenty indicators were assessed, but none were well suited to capturing all of these elements of reliability. A new measure, journey time buffer index (JTBI), was therefore proposed; the index used estimates of wait times at bus stops while capturing variability in wait and travel times that tended to increase the disutility of transit travel. Alternative formulations were developed for short and long headway service, and the new indicator was applied to the London Transit Commission's bus network in London, Ontario, Canada. This procedure demonstrated that the JTBI was better suited to identifying the factors contributing to unreliable service than metrics that focused on a single component of reliability. A linear regression analysis also highlighted that route length, stop spacing, time of day, route orientation relative to the city center, and passenger load all influenced reliability although the low adjusted R2 value of .298 showed that some major causes of reliability were not captured by the model.