There was a political problem. The interstates were spending truly ungodly sums of money in rural area; the whole system cost something like $400 billion - $500

There was a political problem. The interstates were spending truly ungodly sums of money in rural area; the whole system cost something like $400 billion - $500 billion in inflation adjusted dollars. If you were a city, your residents--who tended to be wealthier than rural areas--were footing the bill and getting nothing in return except maybe somewhat lower shipping costs. So what's a politician to do? Easy: extend the highways to cities. In the 1950s the thought was that cars were going to lead us to a glorious future, free from congestion on public transit, so urban leaders gladly paved over their downtowns. There were (and still are) huge subsidies for suburban areas, and other fears were that without these highways cities would be irrelevant as everyone moved to the suburbs and jobs eventually moved with them. In the wake of the planning failures of the 50s and 60s with regards to highways cities moved huge amounts of planning powers to hyperlocal areas and requiring environmental reviews, stopping all the highway nonsense. Unfortunately, it created a new villain in the form of the newly empowered NIMBY.