My guess is that people will just hang onto the cars they already have, or buy compact/subcompact imports. That's especially true now that the price of gas has gone back down for the moment.

IMO, the big 3 made a huge strategic mistake by trying to make people believe (via massive advertising campaigns) that they need 8 passenger 4WD gas guzzlers to drive (alone) a few miles to work. Some people might be becoming more eco-friendly or learning to live on smaller budgets, but not enough to take up cycling: maybe enough to buy a small, (relatively) cheap, reliable car. Most of the people in my neighborhood could get to work on a golf cart if they left 20 minutes earlier. Oh yeah, and if there was infrastructure (for a golf cart).