Urban transportation planning in the United States underwent important changes in the decades after World War II. In the immediate postwar period, federal highway engineers in the Bureau of Public Roads dominated the decision-making process, creating a planning regime that focused almost entirely on the building of modern expressways to relieve traffic congestion. In the 1960s, however, local opposition to expressway construction emerged in cities across the nation, reflecting growing discontent with what many citizens perceived to be a closed planning process that resulted in the destruction of urban neighborhoods, environmental degradation, and inadequate attention paid to alternative modes of transportation. Local freeway protestors found allies in the new U.S. Department of Transportation, which moved in the mid-1960s to absorb the Bureau of Public Roads and support legislation promoting a planning process more open to local input as well as a greater emphasis on federal aid for urban mass transportation. The changing culture of transportation planning produced a series of freeway revolts, resulting in the cancellation or modification of interstate highway projects, in major American cities. Changes in transportation planning played out differently in every city, however. This dissertation examines controversies over Philadelphia's major expressway projects - the Schuylkill Expressway, the Delaware Expressway, and the never-built Crosstown Expressway, in addition to major mass transit developments such as the city's subsidization of the commuter railroads, the creation of the Southeastern Pennsylvania Transportation Authority, and the building of a railroad tunnel known as the Center City Commuter Connection, in order to trace the evolution of the city's transportation politics between 1946 and 1984. Significantly, Philadelphia's own freeway revolt succeeded in eliminating the proposed Crosstown Expressway, which would have created a daunting racial barrier while decimating several low-income African American neighborhoods. The Crosstown Expressway revolt, however, failed to change the overall trajectory of Philadelphia's transportation planning politics, which continued to be dominated by an exceptionally strong alliance between City Hall and large business interests. Philadelphia's turn to mass transit in the 1970s, in contrast to those of other cities, failed to redistribute transportation resources to its low-income residents, mainly because the city chose to devote a massive percentage of its federal funding to the Center City Commuter Connection, a downtown rail tunnel designed to serve approximately 8% of the region's commuters. The prioritization of a rail system serving predominantly affluent white suburbanites left Philadelphia's lower-income population saddled with a crumbling urban mass transit system, demonstrating that, despite a more open planning process and a greater emphasis on mass transportation, fundamental inequalities persisted.