Reassessing the financial and social costs of public transport

Abstract

This paper uses a previously developed spreadsheet cost model which simulates public transport modes operated on a 12km route to analyse the total costs of different passenger demand levels. The previous cost model was a very powerful tool to estimate the social and operator cost for different public transport technologies. However, as the model is strategic based, some assumptions are very basic and idealized and the demand was assumed to be exogenous (externally fixed). When the level of demand is high for the lower capacity public transport technologies, passengers may find the incoming vehicle full and therefore they have to wait more than one service interval. This paper applies queueing theory to investigate the probability of having to wait longer than the expected service headways which will affect the average passenger waiting time. The extra waiting time for each passenger is calculated and applied in the spreadsheet cost model. The speed-flow equation in the original spreadsheet model assumes the speed decreases according to the ratio of the current frequency and the lane capacity which is based on the safety headway without any passenger boarding. However, this may vary in different operating environments. Therefore, the speed equation is improved by moving from a linear equation to a piecewise equation that considers the features of different operating environments. To evaluate the differences after applying these equations, endogenous demand rather than exogenous demand will be investigated by using the elasticities for passenger waiting time and journey time.