I've found that many people don't handle gas prices rationally. Say you have a paid off 2000 15mpg SUV with liability only insurance. 1200 gal at 18K miles/yr
You go buy new Honda fit that gets 30mpg in regular use in response to rising gas prices and you finance the new vehicle. With financing, you're required to have full coverage
In 5 years, you'll lose:
$9,024 in depreciation
$1,200 in interest if you do 8% @ $5,000 financed for 3 yrs
$xxx in required full coverage for the duration of financed ownership.
you'll save $9,000 in gas @ 18,000 mile / year @ $3/gal over 5 yrs.
You'll lose the extra space offered by SUV and the less you drive, the less you save. You hardly break even going from something that gets lousy mileage to a economy sub-compact with excellent mileage.
For most people, I can't see changing a car to get better mileage is going to help them with $$$/mile over the duration of ownership. Fuel has high perceived cost of ownership, but that doesn't mean actual cost is high.
Taking the public transit regularly in concurrent with vehicle ownership for any reason other than convenience (i.e. bus stop conveniently in front of your apt and your work) is a waste. If you drive less, you're simply going to increase the per mile cost of ownership of your car. Even if you don't drive it at all, you can't zero the fixed cost unless it's a junker with next to no value and you cancel the insurance and let the registration expire.
Bus passes are quite spendy, but they're economical alternative to a car if you don't own a car, but if you do, your car will still lose value even with no use, you'll still pay insurance, registration, and opportunity cost of spaced occupied by your car.
I drive around 10,000 miles a year and I get 28 mpg on the average. If the gas price goes up a dollar, my cost of ownership increases $360 a year. Not a big deal.