Accessibility-Based Ethics-Aware Transit Design

Abstract:

We propose a new strategic transit design methodology that places accessibility and equity at the center of the trade-off. By guiding transit design with ethical theories, it promises to improve vertical equity. We consider two ethical principles: the utilitarian principle and John Rawls's egalitarian principle known as the difference principle. A simple 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 entails 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.

Bio:

Dr. Marco Nie is currently a Professor of Civil and Environmental Engineering at Northwestern University. He received his B.S. in Structural Engineering from Tsinghua University, his M.S. from National University of Singapore and his Ph.D. from the University of California, Davis. Dr. Nie's research covers a variety of topics in the areas of transportation systems analysis, transportation economics, and sustainable transportation. Dr. Nie had served as a member of the TRB committees on Transportation Network Modeling and Traffic flow Theory and Characteristics. He is currently an Associate Editor for Transportation Science, an Area Editor for Networks and Spatial Economics, and a member of the Editorial Advisory Board for Transportmetrica-B and Transportation Research Part B. Dr. Nie's research has been supported by National Science Foundation, Transportation Research Board, US Department of Transportation, US Department of Energy, and Illinois Department of Transportation.