Now that Cash For Clunkers is as dead as the gas guzzlers it pulled off the road, let's revisit a more basic money-saving transportation question; why own a car at all?

Impractical to consider going carless? Not for some people, if the continuing growth of time-share autos as popularized by Zipcar and similar services holds. But would it work for you?

We've written about this concept before. Zipcar participants pay a yearly membership fee for the right to rent on a per-hour basis one of a fleet of autos stationed nearby. Campuses are a particularly appropriate locations for Zipcars, because of the high density of population and infrequent demand residents might have for a car.

On the University of Michigan campus, for example, students pay $35 a year plus a $25 application fee to join, which permits them to use one of the Zipcar fleet of fuel efficient cars for $8 an hour ($9 on the weekends), for up to 180 miles a day. Gas and insurance are included, and the company takes care of all upkeep. For students, this also saves them the cost of a parking decal, as well as the problem of coming up with a wad of cash to buy a car.

Sounds like a great deal, eh? Zipcar now claims 325,000 time-share cars members, which has attracted competition. A couple of the largest rental companies in the industry, Hertz and Enterprise, have joined smaller players including Chicago's I-GO in setting up similar offerings.

I wondered how well this concept would translate beyond the campus environment. In my city neighborhood of single-family homes, for example, there are a number of freelancers (yours included) with two cars in the household. Many of us could easily downsize to one if we had a Zipcar handy. How much could we save?

My yearly operating cost to drive my own car = $4,064

• Suppose I drove a Zipcar instead:
• Yearly dues plus application fee = $60
• Hourly cost = 416 hours x $8 per hour = $3,328

My yearly cost to drive a Zipcar = $3,388

My savings = $736

Not as much as I'd hoped, but still, $50 a month more in my pocket would be welcome.

Run the same process, however, assuming I could get by driving two times a week rather than four, and

My savings = $1,508. That's an appealing figure.

So yes, the Zipcar concept could have some appeal even to the middle-class, middle-aged driver, but it all depends on how often you really need to drive. Most people, I believe, underestimate their addiction to their car. The key to making this program work is to use it as little as possible. If you can't give up the habit, you're better off owning your own.