Does Car Sharing Reduce Your Driving?

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A spirited debate broke out a few weeks back on the Car-free Living listserv run by Livable City about the merits of car sharing. Does it reduce driving and car ownership or increase the impetus to drive among the car-free? One poster who didn't own his own car called car-sharing a gateway drug that encouraged him to increase the number of times he uses a vehicle for all manner of trips, while others argued that VMT is reduced when fewer people own their own cars and share more.

Despite an initial analysis of San Francisco's City CarShare service showing an inducement to drive, in large part because early adopters were "self-professed environmentalists and avid cyclists," a 2003 study on car sharing found that over time the service showed the opposite trend.

By City Car Share's second anniversary, 6.5 percent of emember's trips and 10 percent of their vehicle miles traveled were in carshare vehicles.  Mathed-pair comparisons with a statistical control gropu suggest that, over time, member have reduced their total vehicular travel.  Because carshare vehicles tended to be small and fuel-efficient, per capita gasoline consumption and greenhouse gas emissions among members also appeared to go down.

The study also found that 30-percent of members had sold one or more vehicles and that two-thirds had decided not to buy a vehicle.

Adam Millard-Ball of Nelson Nygaard Consulting, who authored the definitive car-share report several years ago for the Transportation Research Board (TRB), cited a recent report (PDF) presented at TRB by Susan Shaheen demonstrating that car sharing removes 4.6 to 20 cars per shared-use vehicle from the transportation network depending on the city. The same report showed that car-share program members increased walking and transit use by wide margins.

"I think that we are confident now that mature, large-scale car-sharing programs bring great benefit in reducing vehicle ownership and vehicle travel," said Millard-Ball

Tom Radulovich of Livable City asserted that there is an environmental benefit to shared cars that is mostly overlooked: the embodied energy of a vehicle, or the amount of carbon required to produce, maintain, and ultimately dispose of the vehicle.

Estimates of the 'embodied energy' of a car vary quite a lot from authority to authority, but could be anywhere from 10 to 40 percent of all the energy a car  A car in the city generally gets driven a lot less than a suburban car. That means that the urban car's embodied energy is a higher percentage of its life-cycle cost, even if the car's overall energy consumption over its lifetime is lower. If a group of people share a small fleet of cars, rather than all purchasing their own cars, they will save energy and reduce their environmental impact, even if their driving habits don't change at all.

Both Millard-Ball and Radulovich were confident that a further car-sharing benefit to land-use policy would become evident as more data is collected.

"In a city like San Francisco that has great constraints on parking, scarce parking is the thing that keeps people from owning a car," said Millard-Ball. "Car Sharing is helping to change the built environment by reducing parking so that we lock in these reductions in vehicle ownership, and not just free up on-street spaces that someone else can take advantage of."

Said Radulovich: "Think of what the city would be like if all of the folks who seldom use their cars were instead to share cars; they would save money, reduce greenhouse gas emissions, and free up tremendous amount of precious urban space."

Streetsblog SF would like to know how you feel about car-sharing services, whether they've changed your transportation choices and travel behavior, whether you've sold your personal car, or held off on buying a new vehicle.  In addition to the comment section below, feel free to send us your story at tips@sf.streetsblog.org

Flickr photo: The Sierra Club