Multimodal pricing and optimal design of urban public transport: The interplay between traffic congestion and bus crowding

Tirachini, Alejandro; Hensher, David A.; Rose, John M. · 2014 · OpenAlex-citations

DOI: 10.1016/j.trb.2014.01.003

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Summary

This paper addresses the complex interplay between traffic congestion and passenger crowding in the optimal design and pricing of urban public transport systems. The authors identify a gap in existing literature, which typically treats congestion and crowding externalities independently. The research aims to determine how these competing forces influence optimal bus frequency, vehicle size, internal layout (specifically the number of seats), and fare structures. The study is motivated by the need to maximize social welfare while accounting for the trade-offs between reducing user waiting times (via higher frequency) and increasing operational costs and road congestion. The authors develop a multimodal social welfare maximization model with spatially disaggregated demand, applied to a single transport corridor in Sydney, Australia. The model allows users to choose between traveling by bus, car, or walking. Key decision variables include bus fare, congestion toll, bus frequency, bus size, fare collection technology, boarding policy, and the number of seats per bus. The model incorporates detailed formulations for travel time, including mixed-traffic congestion using the Bureau of Public Roads formula and bus stop delays modeled via the IRENE simulator. Crucially, the model distinguishes between seating and standing areas, treating the number of seats as a variable that affects both passenger comfort and vehicle capacity. Four utility models are tested to capture varying levels of user disutility associated with crowding and standing density. The numerical application reveals that optimal bus frequency is highly sensitive to assumptions regarding crowding costs and the impact of buses on traffic congestion. The results demonstrate that crowding and congestion act as colliding forces: crowding externalities push for higher frequency to reduce standing discomfort, while congestion externalities (including bus-induced delays to cars and queuing at stops) push for lower frequency. The study finds that if crowding is significant to users, buses should be designed with as many seats as possible, constrained only by minimum space requirements for aisles, doors, and wheelchairs. If planners opt for fewer seats to increase overall capacity, frequency must be increased to compensate for the resulting discomfort. Furthermore, accounting for crowding externalities leads to a substantial increase in the optimal bus fare and a corresponding reduction in the optimal bus subsidy. The significance of this work lies in its comprehensive integration of internal vehicle design and multimodal externalities into public transport optimization. By treating the number of seats as a decision variable rather than a fixed attribute of bus size, the paper highlights the trade-off between comfort and capacity. The findings provide actionable insights for transport planners, suggesting that ignoring crowding costs can lead to suboptimal service designs, such as insufficient frequency or inappropriate vehicle layouts. Additionally, the inclusion of walking as a mode alternative underscores its role in optimizing transport systems under high congestion scenarios. The study concludes that optimal pricing and design must balance the external costs imposed on road users with the internal comfort levels of public transport passengers.

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• traffic density