I don't exactly think that $4 a gallon caused the housing market to collapse...
Four-dollars-per-gallon probably didn't have a significant effect, but at a certain price-point, people start considering accomodations closer to their jobs, local government offices, and businesses. In other words, given a sufficient spike in gas prices, the suburbs start to empty, and urban housing gets packed. It's not necessarily a formula for a total collapse of the housing market, but in the case of a sustained increase in fuel prices, the whole paradigm of build-out-not-up would have to get turned on its ear.
It's getting there though,...it's 3.28 out here in Omaha...$3.18 if you count the E10 I put in my truck.
It's roughly $2.85-per-gallon at the gas station near my apartment, in Knoxville. From that gas station, though, I could spit and hit a tap on one of the major branches of the Colonial Pipeline. Still I'm glad that I average less than a gallon-per-day in petrol use, because sitting on a pipeline or not, I doubt fuel prices have anywhere to go but up.