Service Reliability and Hidden Waiting Time

Abstract

Traditional transit service quality measures separate waiting time from service reliability and thereby underestimate the real cost of waiting and fail to evaluate the effect of unreliability on passengers. This study's analysis of passenger behavior shows that, for short headway service, the cost of waiting involves not only the mean time spent waiting on the platform but also potential waiting time, that is, the additional time that passengers have to budget for waiting. Budgeted waiting time is based on an extreme of the waiting time distribution such as its 95th percentile value, which is extremely sensitive to service reliability. Methods for determining the distribution of passenger waiting time from automatic vehicle location (AVL) data are derived. For long headway service, actual and budgeted waiting times are shown to be related to high and low extremes of the schedule deviation distribution, which can likewise be determined from AVL data. Two other components of long headway waiting, schedule inconvenience and synchronization cost, are also analyzed. Waiting cost functions and waiting time measures that account for both headway and service reliability are developed and are harmonized in a framework that provides a smooth transition from short to long headway waiting. Examples show how service reliability can be measured as a waiting cost and how service reliability improvements can reduce waiting cost as much as a large reduction in headway can.