A Model to Evaluate the Impact of Headway Variation and Vehicle Size on the Reliability of Public Transit

Reliability of public transit systems is a chronic concern for transit operators, authorities, and users, in terms of system utilization and level of service. This paper develops a theoretical model to evaluate factors that influence the reliability of public transit systems and examines their performance based on stochastic variations in passenger arrival, boarding, alighting, and travel time on the regularity of headway along the route with multiple stops. The model is based on a Markov chain technique to obtain numerical estimates of performance. The predictions of this model are verified based on replicating the well-observed phenomenal relationship between the mean and variance of delay experienced by passengers. The numerical examples offer insights into the factors that affect the reliability of public transit systems. This investigation provides a better understanding of determinants of reliability of public transit systems and it can be used as an analysis tool by transit planners to evaluate the effectiveness of various policies.