SPUR’s report Critical Cooling recommends 42 options for reducing local carbon emissions. This is one of them. To learn about all 42 ideas, read the full report

Set Aside Parking Spaces on the Street to Promote Car Sharing

One of 42 options for reducing local carbon emissions, from our report Critical Cooling.

Urbanist Article
Annual savings potential:
Annual public cost:
Public cost per ton:
Implementing agency:
Horizon year:
850 tons
Revenue neutral
Municipal Transportation Agency


  • San Francisco will designate 500 parking spaces for use by car-sharing companies.
  • Car Share participants will drive, on average, 478 miles per year less as a result of membership
  • Each space that the City sets aside for City CarShare or Zipcar will allow a vehicle to be added to the fleet, and each new vehicle will generate 10 new members.


The two car-sharing companies now operating in San Francisco provide members with access to vehicles on demand. Overall, car-sharing members tend to drive less than they did before they signed up for the service. A group of policies could facilitate the continued growth of car-sharing in the city. One of these policies, which San Francisco committed to in its 2008 environment plan, is to make an additional 500 parking spaces available to car-sharing vehicles. Doing so could boost car share membership at little to no public cost, and provide a modest emissions reduction.

What we do now
Two car-sharing companies, City Carshare and Zipcar, now operate large fleets of vehicles in San Francisco. Their continued expansion, particularly into underserved neighborhoods, is limited by a number of factors, including parking availability.

What we could do
Car-sharing provides individuals with access to a fleet of shared vehicles, allowing them to avoid owning a car, or a second or third car. Policies to promote car-sharing can provide individuals with improved transportation choices while decreasing their overall VMT, and thereby reducing greenhouse gas emissions. For car owners, the price of vehicle purchase and insurance are sunk costs, and the only costs that tend to be considered when making travel choices are the costs of gas and parking. This provides an incentive to choose driving for many marginal trips. Car-sharing participants, by contrast, pay all the costs of vehicle operation on a per-mile or per-hour basis. They can therefore more rationally weigh the costs and benefits of different travel choices for each trip.

Localities can promote car-sharing through several policy changes: Reserve city-owned parking spaces for carsharing vehicles. Establish car-sharing through new development. Replace city vehicle fleets. Provide marketing support and other incentives. Cost
Car-sharing has been successfully implemented in many American cities, workplaces, and universities, and has proved financially self-sustaining. Two car-sharing companies, City Carshare and Zipcar, now operate in San Francisco. In its 2008 environment plan, the city committed to providing 500 additional parking spaces for car-sharing vehicles.1 The market price of 500 parking spaces in San Francisco is very high. However, the direct cost to the city of making these spaces available will probably be negligible.

Carbon savings potential
Research demonstrates that joining a car-sharing program tends to reduce overall VMT. In a study of the members of City CarShare, total VMT initially increased because early adopters tended to be transit advocates who were not car owners. However, in the second year of the program, as the program attracted a more mainstream membership, members’ daily VMT (weekday/workday) fell from 2.80 to 1.49 miles.2 This is a 47 percent reduction.

If VMT fell by 1.31 miles per person per day, annual VMT saved per person would be 478. If we assume that an additional car-sharing vehicles would facilitate 10 new members per vehicle, the city investment would yield 5,000 new car share members. The total VMT savings per year would be 2.4 million, and total CO2 emissions reduction would be 850 metric tons.

1 “SFFoward, Building a Bright Future, Environment Plan 2008.” www.sfgov.org/site/uploadedfiles/mayor/SForwardFinal.pdf
2 Cervero and Tsai, 2003