Back in the old days, when kids wanted to go somewhere, they jumped onto their bicycles and off they went. They didn't know — and didn't care — that they were using the "greenest" mode of transportation available.

Those kids are grown up now, battling traffic in their gas-guzzling SUVs. A run to the office or around town on errands covers mileage only a Lance Armstrong could achieve without a motor.

Nowadays riding a bicycle is simply out of the question for most. Because of the distances involved, it might as well be uphill both ways.

There has to be a greener, more efficient way to get around that's like the good old bicycle — healthy, cheap and more exhilarating. Could the scooter, extremely popular in Europe and Asia, bring back that free feeling and rush of adrenaline without damaging the environment?

Maybe not.

"In general, scooters are not as good a deal for the environment as they seem to be because of how much they pollute," says Bryan Welch, publisher of Mother Earth News, an environment-minded monthly magazine.

So how can such a zippy little machine that gets double the mileage of cars and triple that of SUVs be a bad deal?

According to the Environmental Protection Agency, most people who think scooters and motorcycles are less polluting than four-wheelers fail to take into account the sophisticated emission controls found in most cars today.

"Because of the size and design of scooters, you can't have the catalytic converters and emission controls that you can in a car," explains the EPA's Cathy Milbourn. "Scooters produce fewer greenhouse gases such as carbon dioxide (CO2), but produce significantly more hydrocarbons (HC) and nitrogen oxides (NOx)."

According to current EPA standards, cars are allowed to emit 0.16 grams of HC and NOx per mile. Scooters can get away with emitting 1.3 grams per mile — more than eight times the amount of cars.

HC and NOx are precursors to ground-level ozone and ultimately smog, a serious problem in cities across the United States. Ground-level ozone is formed in sunlight by reactions that include HC and NOx.

Ozone has been known to cause health problems such as lung damage, difficulty breathing and poor cardiovascular functioning. Some hydrocarbons can cause cancer or other health problems. And scooters are most likely to be used in warm weather, when ozone levels are already high.

Then again, smog and ozone, longtime bugaboos of the environmental movement, have taken a backseat to a new, more pressing problem — carbon dioxide-induced global warming.

"Ozone is more of a concern closer to the source of output such as urban settings. Globally it's less of an issue," explains Welch, "But ozone is not a top priority right now. What is most important is burning less fossil fuel."

Burning less fossil fuel directly lowers the amount of CO2 put into the atmosphere, cutting back on a major greenhouse gas. It also would reduce our dependence on foreign oil producers.

Piaggio Group Americas, Inc., stateside subsidiary of the Italian maker of the iconic Vespa scooter, makes its case very plainly.

"If Americans used a Vespa for 10 percent of their everyday travel," the company declares, "they could reduce national fuel consumption by 14 millions gallons per day and decrease CO2 emissions by 324 million pounds per day."

Since scooters made after 2006 produce, on average, 72 percent less CO2 than the average car and 78 percent less than the average SUV, things are looking greener.

"At the end of the day, it would be a net gain for the environment if more people would ride scooters," says Welch. "A good rule of thumb is to go on how much fuel you burn — if it burns less it's better for the environment."