When did this expression become popular? To me a trip is a trip, but some seem to feel the need to specify their mode of travel. I don't remember hearing it before about 1990. Comments, anyone?

The OED Online's earliest citation is from a 1961 Newsweek: "He broadened teammates' minds by reading sensitive passages aloud during road trips."

Tinman

I think the Newsweek quote gives the clue: a road trip is something a team or a (rock, jazz) band does, presumably as opposed to touring by rail or air.

My gut feeling is that road trip is quite old -- i.e. reaching back into my neolithic youth. I get a vague memory of road trip applied to, say, the Glenn Miller Band etc. in the forties.

David