I will believe that fuel prices are high when I see that people stop wasting it and drivers slow down to the legal speed limit. When people start looking at getting a smaller RV instead of a bigger one so they have room for a 40" TV (or two).
Our "RV" averages 15 MPG and there are the Class B motorhomes like the Roadtrek that are built on the Mercedes platform and with the 5 cylinder diesel engine that average over 25 MPG. That assumes that people can forgo some of their creature comforts and the bigger is always better mentality.
Gas and diesel are more expensive in Europe but then they have protected pensions, free university schooling, free medical, great mass transportation systems (London to Venice entirely by high speed rail at 200 MPH), and work a month less per year than in the USA, and they live longer and they don't have to worry about their sons and daughters going off to fight and die or be permanently damaged in foreign wars for oil, so I guess it evens out.