I think it would take several generations of education before the majority of Americans would even consider giving up their cars, even for a portion of the time. As long as society continues to teach people that driving a gas-guzzling SUV is somehow patriotic, we'll never make any progress.

Additionally, far too many Americans truly believe that cyclists are a bunch of selfish weirdos who seem to think they have a right inconvenience motorists by using roads to practice their eccentric hobby. Damn them!

And I'm not sure the economic collapse / poverty / increased gas prices will have much of an impact either, unless it goes on for decades. I recall reading a fluff piece in the local fishwrap about a poor woman who was struggling to make ends meet. The heart-wrenching story explained how she had to choose between buying food for her child and putting gas in her car. She needed gas for the car so she could get to her part-time job, which was her only source of income. Oh, the humanity.

Buried several paragraphs in, was that her job was a whopping 3/4 of a mile away from her home. And yet the idea that she could get off her fat ass and walk there didn't even occur to her. I doubt people like her would ever ride a bike, no matter what gas cost.