In this paper we proposed a corridor transit design model 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 reviewed and examined four different ethical principle but were focused on the utilitarian principle (the status quo) and John Rawls’ difference principle (a form of egalitarianism). The main findings from our analysis of the design models are summarized as follows.

• When the transit service is homogeneous in space, the utilitarian design model and the egalitarian design model are mathematically equivalent. Thus, they always produce identical designs for all forms of the opportunity distribution.
• With supply heterogeneity, the egalitarian design has a prominent equity-enhancing effect, whereas the utilitarian design tends to exacerbate inequity, especially in presence of large innate inequality.
• Correcting innate inequality by applying the egalitarian principle often entails interventions that appear more “discriminatory” than the status quo. Whether such distributive measures are justified, the appearance of unfairness can be met with skepticism, if not outright opposition, from the general public.
•  Our ability to promote equity is restricted not only by the resources available but also by the structure of the problem at hand. The difference principle is useful because it defines the upper limit of equity that we may strive to reach but should not exceed.

It is worth recalling the egalitarian design based on the difference principle tends to reduce the total accessibility of all residents, compared to the incumbent design regime of utilitarianism. When innate inequality is large, the loss of accessibility can be substantial, up to 40\% according to our experiments. This, of course, is hardly a surprise, given the primary concern of the difference principle is the distributive justice, not the total utility. One thing is clear though: the benefits to the most disadvantaged could come at a hefty price to society writ large. Steven Dubner, the host of the popular podcast Freakonomics, likes to quip,

Economists know the price of everything but the value of nothing.

No doubt the same can be said about many if not most engineers. In some sense, our study constitutes an attempt to price social values in engineering practice. To be sure, these values are priceless to many an advocate, who would be quick to point out that the obsession with pricing everything is precisely what got us here in the first place. However, understanding the consequence of imposing certain values in engineering systems is still a crucial task, if only because we always need to secure public support or determine affordability.

The work is partially funded by Northwestern University’s Catalyst fund and NSF’s Smart and Connected Community (S&CC) Planning
Grant.  A prerprint of the paper may be downloaded here.