The impact of irregular headways on seat availability

This paper introduces seat availability reliability, a new reliability measure that assesses the performance of transit lines. This alternative reliability indicator is defined in terms of the coefficient of variation, which examines the relative deviation of seat availability. An analytical approach is utilized based on the conditional expectation to achieve relationships for the mean and variance of the number of boarding and alighting passengers and seat availability at stops. Furthermore, confidence intervals for seat availability are derived. It is proposed that such information might be useful for traveler information systems. The proposed model is applied to a schematic transit line to show how sensitive seat availability is to headway variation (irregular dispatching) and demand uncertainty.