Well, actually it is one of three birthdays you can celebrate this year. On this date in 1956, President Eisenhower went before Congress and asked for the creation and funding for a national interstate system.
On June 29th, Congress passed the Federal Aid Highway Act, and on August 13, actual construction began on a stretch of I-70 by St. Charles, Missouri, a suburb of St. Louis. (This was on a section of the RT 66 bypass.) There are markers at the spot commemorating the event.
This is regarded as the biggest public works effort in history. This was great news to motorists and truckers, but definitely not so great for Route 66 which met its demise as a result. However, I wouldn't even want to consider how bad driving anywhere in the US would be without them. Imagine how bad traffic would be today if we were still relying on the existing roads of the time.
For more information on the interstates, Eisenhower's reason for establishing it, and plenty of trivia, go to this site:
Keep on that big OLD multilane asphalt Highway and Happy B-Day.-RoadDog