Accessibility-based ethics-aware transit design

Abstract

This study proposes a new strategic transit design methodology that places accessibility and equity at the center of the trade-offs. By guiding transit design with ethical theories, it promises to improve vertical equity. We consider four ethical principles: the utilitarian principle, the sufficient principle, the maximax principle, and the difference principle. As the last three are all related to egalitarianism, the difference principle is selected as the representative. A parsimonious corridor transit design model is developed that differentiates travelers according to their location-based access to opportunities. Its objective is defined by the underlying ethical principle: maximizing the total accessibility for the utilitarian principle and maximizing the accessibility of the most disadvantaged for the difference principle. When transit service is homogeneous everywhere along the corridor, we prove ethical principles make no difference in the optimal design. In response to this finding, spatial supply heterogeneity is introduced into the design models. We then find the egalitarian design has a prominent equity-enhancing effect, whereas the utilitarian design exacerbates inequity, especially when the spatial distribution of opportunities is highly uneven. The results highlight the usefulness of the difference principle, notably its ability to identify the upper limit of equity when the decision is bounded by limited resources or the underlying structure of the problem at hand. However, correcting innate inequality by applying the difference principle may entail interventions that not only appear “discriminatory” but also impose a steep price in the form of lost total accessibility—up to 40% in our numerical experiments.