Years ago I watched a documentary called Divided Highways (1997), which I recommend for a quick overview of the system. One of the interviews was a transportation planner whose job was to locate the expressways through and around cities. Planners were trained to find the least expensive land, so no surprise that they often bisected the poorest, least connected neighborhoods. In Chicago the highways often ended up reinforcing segregation lines. Nothing like an 8 lane highway to discourage a casual stroll.
Speaking of planning, I found a study of New Orleans which considered a raised highway along the waterfront, effectively blocking off Jackson Square. The best part was an analysis of how much scenic New Orleans the drivers would be able to enjoy as they whiz past.