An axiomatic characterization of fairness in transport networks: Application to road pricing and spatial equity

This paper considers the important issue of fairness in transportation. Designing fair policies in transportation is critical since transport networks are generally recognized as public goods. Moreover, the effects of road pricing may be significantly different for travellers from different geographical regions. Hence, any revenue collected from road pricing or infrastructure funding policies ought to be appropriately redistributed among the population of different geographical regions. In this work, we focus on spatial equity in the road pricing revenue assignment problem. We examine well-known fairness schemes commonly discussed in the literature: opportunity fairness, proportional fairness (individual value and marginal value), and market fairness. We conduct an axiomatic characterization of these schemes to demonstrate their properties and highlight their policy implications. We then present a practical implementation of the proposed fair pricing revenue assignment mechanisms on Winnipeg's downtown network. The results reveal that market fairness is the most axiomatically restrictive scheme and that this scheme is related to individual value and proportional value proportional fairness under specific conditions. We also demonstrate a paradoxical situation where a market or marginal value proportional fair assignment requires a certain group to pay taxes, because they receive more benefits than other groups. In turn, opportunity fairness is shown to be the least restrictive revenue assignment scheme and to require minimal computational resources.