For those times you do drive, you can take steps to increase mileage and even reduce emissions. Remember, the more gas a car uses, the more harmful emissions it's putting out.

Until zero-impact cars or fuels are invented, here's a list of things you can do to improve fuel efficiency:

• Aggressive driving, including rapid acceleration off the line and through traffic, wastes gas and increases emissions. Maintaining a smooth — and legal — pace will get you more miles to the gallon.

• Every car reaches its optimal fuel efficiency at a different speed, but it's generally around 60 miles per hour. According to the U.S. Department of Energy, for every 5 miles an hour you drive over 60 mph, it's like you are spending an extra 20 cents per gallon of gas.

• Carrying around heavy loads reduces a car's gas mileage. It makes more of a difference in smaller cars than larger ones because the weight carried is relative to the weight of the car.

The National Highway Traffic and Safety Administration calculated that the average mileage only increased 1.6 miles per gallon (mpg), from 23.1 mpg in 1980 to 24.7 mpg in 2004. The improvement could have been larger, but the huge successes of SUVs, relatively inexpensive gas, and more people idling in traffic brought down the mileage calculations (but did not decrease emissions).

• Idling, burning gas, and getting nowhere wastes gas. If you need another reason to avoid drive-through windows, consider this. Idling for longer than a minute or two actually uses more gas than starting the car, except in the case of hybrids. If you just have to get that burger and fries, you can park and walk inside instead.

Properly maintained engines operate more efficiently and get better gas mileage. Air filters remove impurities from the air before they can reach the car's engine. Clogged filters can allow some impurities to get through and reduce gas mileage. Finally, properly inflated tires are not only safer to drive on, they improve mileage, too.