What interstate has been traveled on by the highest percentage of Americans?

[Gnutella]

I-27.

Maybe, but I'm thinking I-99 might have it beat...
In all seriousness, my guess is it's I-95. Over a hundred million Americans live near it.

But seriously, I-99 passes by State College, and Penn State has students and alumni from many different states.

I know that I-27 serves Lubbock, which has Texas Tech, but it's smaller and more geographically isolated than Penn State, and it doesn't have as high of a profile globally or nationally.

[Kulerage]

I'm going to have to go with the majority and say I-95. With how heavily populated the eastern part of the country is compared to the west, and with how many population centers that it passes though, I'd say that I-95 is pretty much unavoidable for your entire life there.

[GaryV]

But seriously, I-99 passes by State College, and Penn State has students and alumni from many different states.

I know that I-27 serves Lubbock, which has Texas Tech, but it's smaller and more geographically isolated than Penn State, and it doesn't have as high of a profile globally or nationally.

Those places may have a few people from a high percentage of states.  But not a high percentage of the total US population.