Even though U.S. pump prices are nearly half the $4 per gallon ($1.06 per liter) levels of a year ago, the legions of American fans of gas-guzzling SUVs and trucks don't have much to celebrate.

President Barack Obama's White House has unveiled new fuel-efficiency rules that will push auto companies into making more small cars and General Motors and Chrysler -- both heavily associated with large vehicles -- have sunk into bankruptcy.

But don't expect many dents in the Sport Utility Vehicle fan club.

Cities like Houston, where driving is at the heart of the daily routine, are proof of the American love affair with the big car.

I couldn't get by without this thing, said Kathy Fieldman, a mother of three who was washing her black Chevrolet Suburban at the Bubbles Car Wash in Houston.

Obama can do whatever he wants -- I need to get my kids to school, she said. I can afford to put gas in it, especially where it is now.

GM, the country's No. 1 automaker, filed the biggest bankruptcy in history by a U.S. industrial company on Monday under the direction of the Obama administration. Fellow Detroit auto giant Chrysler had filed for creditor protection in May.

GM's move came weeks after Obama ordered the struggling auto industry to make more fuel-efficient cars under tough new national standards to cut heat-trapping carbon dioxide emissions and increase gas mileage.

GRADUAL CHANGE

The new fuel rules and Detroit's economic hardships will transform the face of the U.S. auto fleet over time and nudge Americans toward smaller models, said Joe Wiesenfelder, a senior editor at Cars.com.

But the change will be gradual and driven by financial, not environmental, concerns.

People who have Hummers and pickup trucks don't need to dump them and get a (Toyota) Prius, he said. When it's time to buy something new, they are absolutely going to get something more efficient -- even if it's one size smaller.

For the typical two-car American family, one might be an SUV for local trips and the other a smaller, more fuel-efficient model for long-haul excursions, he said.

For many Americans, the choice between buying an SUV or a fuel-efficient hybrid seems to be about meeting family demands of carpools and soccer games.

There's still an SUV market in Texas, said Michael Wolf, a salesman at Sterling McCall Toyota, beside a bustling highway where 20,000 people commute to Houston from the suburb of Sugar Land every day. There are all those families with two and three kids down in Sugar Land. 

But if gas prices return to last July's record U.S. average of $4.11 a gallon -- versus about $2.44 a gallon now -- SUV drivers might have little choice but to seek lighter cars.

No one had to tell people who were spending $100 a week to fill their tank that this isn't sustainable, Wiesenfelder said. That is not a lesson that people forget.

For Dan Bryant, a member of the Houston Hybrid and Hypermilers Club and owner of a 2007 Toyota Prius, using a fuel-efficient car for his 15-mile (24-km) commute from his home in Cypress, Texas, has little to do with ecology.

I'm not the stereotypical hybrid owner, he said. My primary motivation has nothing to do with the environment or polar bears.

Instead, Bryant said he drives a hybrid to help cut U.S. dependence on crude oil imports.