Car-sharing can be a great alternative to ownership for those who don't need a car very often, and for those who want to help the environment. Not only do you avoid a monthly car and insurance payment, but you can also avoid parking fees and expensive maintenance and repairs.

For the present car-sharing is only available in big cities like Atlanta, Chicago, San Francisco, and New York.

There are several different car-sharing programs currently available in the United States, including the Zipcar, I-go, and Hertz on demand (previously known as Connect by Hertz).

Car sharing provides a green alternative to car ownership especially in larger cities that provide other travel alternatives like buses and subways.

Even with public transportation available in these cities there may be times when you need a car for a few hours or a couple of days, but don't use a car enough to make buying one a viable option. Car sharing prevents more vehicles from being put on the road than are necessary, and in big cities may one day greatly reduce traffic jams and air pollution.

Zipcar is currently available in major cities in 32 US states and is also available in London, Vancouver, and Toronto.  For every one Zipcar approximately fifteen privately owned cars are kept off the road. Zipcar membership is very easy to obtain provided you have a valid driver's license and debit or credit card. They have different membership plans suited to how much you need to drive.

After you receive your zip-card  you will be able to make reservations for a car any time. Your reservation includes gas, insurance, and 180 miles a day. You are of course able to drive more miles than that for a small fee. To find out more about zipcar visit www.zipcar.com.

Currently I-go is only available in the Chicago area. I-go offers a variety of cars from standard vehicles, to hybrids, and total electric vehicles. When you join you choose the membership plan that best suits your needs. I-go also offers special plans for businesses.

I-go cars are available twenty-four hours a day, seven days a week, and you can make reservations online. I-go covers the price of insurance, gas, maintenance and twenty-four hour roadside assistance.

If you are in the Chicago area and wish to learn more please visit http://www.igocars.org/how/faq/ .

Hertz on-demand (previously known as Connect by Hertz) is available in select cities in nine states, Spain, France, Germany, Canada, and the United Kingdom.

They offer a free membership with rentals available by the day or by the hour, gas, insurance, and 180 miles per day are covered in the rental agreement. Hertz offers both standard and green vehicles for you to choose from.

Car-sharing is certainly not for everyone, but it does seem to be growing in popularity. This is certainly a greener and less expensive option for drivers who only occasionally need a car. If this sounds like something that might be good for you look into car-sharing options in your area.