Every now and then I browse around on YouTube looking for this and other things, and today I found it! It's "GM Motorama Exhibit 1956
At the 1:35 the teenager wonders what it would be like in 1976, and the scene changes to that "far future". He refers to his car as a "Firebird", which is where I got the thought it was a T-Bird. And just like I remember, there is a ludicrous lack of traffic on the highway, and an actual live person giving him detailed personalized directions.
I still have no idea where I originally saw this, though.
This one can be moved to Solved.