When Coloradans traded in their old cars for new ones in the federal "Cash for Clunkers" program, they received an average 9.8 miles per gallon increase in fuel efficiency. About 40 percent of those folks waved goodbye to gas-guzzling SUVs and opted instead for passenger cars.

That's certainly good news. But don't think the billion-dollar federal program did anything to measurably improve the environment.

In reality, the program only helped a relative few select consumers.

First and foremost, the "Car Allowance Rebate System" was designed to help the ailing car industry. Auto dealers around the country got a one-time boost, and some argue the surge in sales helped jump-start the economy.

But the program also intended to reduce carbon dioxide emissions, reduce America's dependence on foreign oil, and improve urban air quality.

"Don't pretend it helps the environment," says professor Don Stedman at the University of Denver. Stedman has been studying vehicle emissions around the country and the world since 1987. He and other air quality specialists agree the $3 billion program was too expensive for what it achieved.

CARS was just too small to have any real impact on global warming or pollution. An Associated Press analysis predicts the program will save about 2.1 million tons of carbon emissions a year. That seems enormous — until you realize the nation's discharge is 6.4 billion tons.

More than 4.9 million vehicles are registered in Colorado, so the estimated 8,000 vehicles replaced is just a drop in the bucket.

While it is true vehicles older than five years cause much of today's urban air pollution, Stedman believes the program wasn't specific enough to make a difference.

Most cars today aren't big polluters, he says. In fact, about one-half of current emissions come from only 2 percent of the cars on the road, and those aren't necessarily old. He cites some taxis as an example: They might be newer vehicles, but they are broken, high mileage cars that pollute. Owners don't want to fix them because days in a repair shop means less income.

He also believes most CARS participants traded in vehicles that had less value to them. "The more you drive a vehicle, the higher value you place on it," he says. Some people traded in the cars they kept parked in the back yard. So those vehicles, even if they were big polluters, spent little time contributing to the emissions problem.

Also, the program allowed wealthier folks who probably planned to purchase new vehicles in the coming years to snap up the limited rebates. The most common car turned in was the Ford Explorer.

The program also ignored the biggest polluters and those Americans who could have benefitted most: Those with lower incomes who drive old "clunkers," not Ford Explorers.