Distributive impacts of demand-based modelling

Transport demand models play a crucial role in the distribution of transport facilities, and hence accessibility, over population groups. The goal of this article is to assess the distributive impacts of the widely-used four-step, demand-based, transport model. This article starts from the hypothesis that the consecutive application of the four-step model over a number of years, and successive investments in transport infrastructure consistent with the model results, will widen existing gaps between high-mobile and low-mobile groups, in terms of transport facilities and accessibility available to each group. A simplified fourstep model is then developed to test the hypothesis under different policy scenarios. The results are mixed. In each scenario, gaps between high-mobile and low-mobile groups are increasing and decreasing at the same time. Against expectations, the distributive implications of demand-based modelling seem to depend on the situation and the focus of analysis. Given the unpredictable distributive impacts, it is suggested that explicit justice indicators be incorporated in transport modelling if it is to contribute to a more just distribution of transport facilities and accessibility over population groups.