Sadly, Wikipedia says it is not true. See here:

http://tinyurl.com/yz66ej

http://www.tfhrc.gov/pubrds/mayjun00/onemileinfive.htm

It occurs to me that the previous comments only addressed whether the interstate highway system was intentionally built with one mile in five being straight so aircraft could land on it. This is an unresponsive answer, because the question ahd to do with Air Force training, not with the layout of the interstate system.

I would imagine that because all pilots are taught about alternate landing sites, pilots would naturally consider straight stretches of interstate highway as potential emergency landing sites, even if two lanes plus shoulders is rather narrow for a modern jet airliner or bomber.

But the question asked whether or not this was specifically included in Air Force pilot training. I wish I knew the answer, but I was a jarhead.

The Germans used the Autobahns at the end of World War II as airstrips, and the Luftwaffe continued to practice from time to time using the highways during the Cold War. Other Air Forces have done the same during times of tension or crisis, such as the Taiwanese and the Pakistani. I have never heard, however, that USAF ever used American highways as dispersal airfields.

Let me add something to my post. The Germans did mark the sections of the Autobahn that could be used as airstrips, whereas the Interstates don't have markings. The importance of the markings is that pilots would have to know where it would be safe to operate--that is, no overhead power and telephone lines that are almost impossible to see from an aircraft. So, unless someone has ever seen airstrip markings on the some section of the Interstate system, you can be pretty sure that the US Armed Forces were not planning on using highways for dispersal airfields.

I have never heard, however, that USAF ever used American highways as dispersal airfields.

All of the freeway/highway landings I've ever heard of (around here, it seems to happen once every 2-3 years, on average) have been civilian aircraft having an emergency, never a USAF (or any other military) aircraft training.