It takes time for people to buy new cars. Any reasonable oil price doesn't cause people to junk their cars for new ones, it just causes them to consider it more carefully next time they buy a car. If the average car is on the streets 5 years, then you'd expect this whole cycle to flip over in about 5 years, but wait, it's worse than that. First there has to be demand (a year of high gas prices, with no end in sight convinces consumers that they need a more efficient car), then there needs to be redesign, and retooling, and if things keep up, in 3-4 years, new efficient cars are being produced in large numbers. So, all told, I think it takes around 10 years, give or take, and the price has to stay consistently high for all or most of that time. If that were to happen, then VMT would start to fall and efficiency would start to rapidly climb.

Also, GM and Ford would start to rapidly enter chapter 11, as their executives are hell bent on producing gas guzzlers even if it kills them, which it of course has indeed been doing.