He probably meant Interstates, and 1956 is 60 years ago, which is why I'm guessing that. Interstate 5 (Seattle portion) was only completed in 1969[0] so depending on where you are, it could be significantly less.
Good point. I-80 wasn't complete coast-to-coast until 1986.
There were gaps in the Western sections for years. That was the first coast-to-coast Interstate, the old Lincoln Highway route. I-40, the "Route 66" route, was completed even later.
[0] - http://www.historylink.org/index.cfm?DisplayPage=output.cfm&...