Use Car-Sharing Instead of Owning
Join a car-sharing program like FlexCar or Zipcar and you may never need your own car again. Parked in dozens of locations around San Francisco (and other cities), you reserve a car online, go to the car, swipe your car and drive off. You don't pay extra for gas or insurance.
It's estimated that each shared car put in service takes about 15 other cars off the road. Flexcar for example has a fleet of Ultra Low Emission Vehicles and fuel-efficient hybrids averaging more than 30 miles per gallon