[Not that facts should ever be permitted to get into the way of an argument supporting greater socialization of the US economy, but the federal government didn’t build interstate highways in the 1950’s. Superhighways in the 50’s were built by the states. The construction cost was financed through the sale of bonds into the private marketplace.]
Really? They might have built them, but according to this the funding was 90% FEDERAL GOVERNMENT.
The Dwight D. Eisenhower National System of Interstate and Defense Highways, commonly called the Interstate Highway System (or simply the Interstate), is a network of limited-access highways (also called freeways or expressways) in the United States. It is named for President Dwight D. Eisenhower, who championed its formation. As of 2006[update], the system has a total length of 46,876 miles (75,440 km),[1] making it both the largest highway system in the world and the largest public works project in history.[2] The Interstate Highway System is a subsystem of the National Highway System.
While Interstate Highways usually receive substantial federal funding (90% federal and 10% state) and comply with federal standards, they are owned, built, and operated by the states or toll authorities.
Those of us who actually remember that era will recall that the first 3,000 miles or so of what later became the interstate highway system were built by the states without federal involvement and were privately financed. While the law authorizing federal financing of the interstate system may have been passed in 1956, construction largely took place in the 60's and 70's.
Federal financing of interstates might, however, provide us with an accurate prediction of how the high speed rail boondoggle will turn out (as if Amtrak isn't sufficient). The interstate system approved in 1956 was predicted to be completed in 12 years at a cost of $25 Billion. It took 35 years at a cost of $114 Billion.