As soon as the Highway Act was passed in 1956, interstate highway routing became part of the political process. Although highway engineers portrayed the decisions they made in highly technical and scientific terms, through studies on traffic counts, economics, strategic interregional connections, and defense; the reality is that highway routing was, and still is, a highly political activity, based as much on socioeconomics, power, and racial bias, as it was on technical engineering principles. Interstates went where powerful white men wanted them to go. Conversely, places that powerful white men wanted to remain disconnected, or without access, remained so.
As interstate highways moved from idea to reality in American cities, many urban mayors and state governors lobbied Congress to route highways close to downtowns for economic development reasons. Through the political process, increasing numbers of highways were planned in direct alignment with urban areas, especially near downtown and through minority and low-income neighborhoods. As urban interstate routing got closer to being finalized, the politics of power played out at a more local, intimate scale. State and local engineers were very important actors in routing decisions because they were more familiar with local land use, economics, and social circumstances than federal highway engineers.
In many cities, urban interstate construction also coincided with dramatic shifts in demographics and local racial politics. In the South, interstates were being routed through cities at the same time that civil rights activists were encountering violent reactions from white government officials to their demand for change. The laws that had legalized segregated public transportation on trains and buses were being strategically challenged. In the North, highway routing coincided with migration of African American refugees from Southern violence, murder, and incarceration.
While some highway routing through white neighborhoods was unavoidable, state and local highway engineers found it politically desirable to avoid as many white neighborhoods as possible. African Americans and other people of color lacked political power, and in many places were actively and violently targeted, so routing highways through their neighborhoods became not just a byproduct of highway routing, but a goal of it. This was described as the removal of urban blight, a condition validated through other planning documents and tools of oppression such as red lining.