If gas in the US ever hits 5-10 dollars a gallon, people will walk, people will use public transport and bikes, they will do whatever they have to do to use whatever isn't current practical. For now.. Gas works fine.
I suspect you're completely wrong there, people will still use it just as before - it's that price elsewhere, and it has had very little effect on consumption.
Currently petrol here is about $9 a gallon, although ours are proper gallons of course