“It is broadly accepted that fairly dense urban development is an essential feature of a successful public transit system. However going beyond this generality to specific guidelines on where, when, and by how much to increase urban densities is never easy. This paper investigates the relationship between transit and urban densities in the United States from multiple perspectives. While empirical evidence suggests that recent-generation rail investments in the U.S. have in many instances conferred net social benefits, considerable skepticism remains, particularly among the more vocal critics of American transit policy. All sides agree that increasing urban densities will place public transit on firmer financial footing. Our analysis suggests that light-rail systems need around 30 people per gross acre around stations and heavy rail systems need 50 percent higher densities than this to place them in the top one-quarter of cost-effective rail investments in the U.S. The ridership gains from such increases, our research showed, would be substantial, especially when jobs are concentrated within a quarter-mile of a station and housing within a half-mile. For smaller cities, such densities are likely politically unacceptable, however, as suggested by the reactions of stakeholders in Stockton, California to photo-simulations of higher densities along proposed BRT corridors.”