As the price of the highway system grew by billions and billions of dollars, accusations of corruption ran rampant. Other controversies included estimates that up to 15,000 families and 1,500 businesses were being displaced every year as the project raced towards its completion.

By the end of 1962, 14,300 miles of the interstate system had been opened, and a year later that jumped to 16,600 miles. Today more than 46,000 miles are in operation. The price of construction was pegged at $129 billion, as estimated in 1991, which is the equivalent of around $285 billion in today's money. The longest interstate is I-90, which connects Boston to Seattle over more than 3,000 miles.

Read about other country-changing megaprojects from across the world

America's biggest past megaprojects