More Parking Means More Driving

It is very obvious that people are more likely to drive if they can find parking easily at home and at their destination, but I have had many arguments with people say, "People will drive anyway.  They will just spend more time circling looking for a space if there is not enough parking." I am glad that there are finally some statistical studies showing that availability of parking is a very strong cause of increased driving.

One study looks at parking supply from the 1950s to the present in nine cities (including Berkeley, California, where I live), and it infers causality by using a statistical method commonly used in epidemiology. It concludes, "At the city scale, we find that an increase in parking provision from 0.1 to 0.5 parking spaces per resident and employee is associated with an increase in commuter automobile mode share of roughly 30 percentage points." See the study (PDF).

A second study looks at residential parking in New York City.  It concludes, "The research shows a clear relationship between guaranteed parking at home and a greater propensity to use the automobile for journey to work trips even between origin and destinations pairs that are reasonably well and very well served by transit." See the study (PDF).

A third study looks at parking at residential, retail, and office uses in San Francisco. See the study (PDF). In all cases, driving is a function of both parking and of the design of the land use. It finds that parking has slightly different effects for these different uses:

• Residential: for a site with moderate auto orientation, the absence of parking is associated with a 35% reduction in auto mode share.
• Retail: for a site with moderate auto orientation, the absence of parking is associated with a 30% reduction in auto mode share.
• Office: for a site with moderate auto orientation, the absence of free or subsidized parking is associated with a 32% reduction in auto mode share.

 As for the claims that the remaining drivers will waste gasoline and generate pollution by circling and looking for parking, anyone who follows city planning issues knows that Donald Shoup has shown that we can eliminate this problem by pricing parking (including on-street parking) properly.

Of course, the correlation would be much higher if we built car-free housing located in areas with permit parking - housing whose residents do not have on-site parking and are not able to buy permits for on-street parking.  In this case, the people without on-site parking would not drive at all.

San Francisco is going to act on this new research about parking. It has already adopted Shoupian pricing of parking in parts of the city.  Now, it is planning to limit provision of parking to limit automobile use.  A report by the SFMTA says about these studies of parking provision and driving:

This information comes as San Francisco is in the midst of one of its biggest new-housing construction booms in history, projected to add 100,000 households and more than 190,000 new jobs by 2040. If everyone arrives with a car, that’s going to be a recipe for gridlock and economic stagnation. The effects on the environment, quality of life and pedestrian safety will be substantial. The city will grind to a halt.

Fortunately, city officials have been planning for this growth on several fronts, including the Transportation Sustainability Program. This three-part program is designed to invest more in our transportation system, align our environmental rules with policy goals like emissions reductions and smart growth along transit, and shift choices to makes it easier for people to get around by transit, walking, biking, or car-sharing.

The growing research on the link between available parking and people’s decision to drive is part of the data the SFMTA, Planning Department, and San Francisco County Transportation Authority are considering as they work on legislation that will help shape future development in the city and provide incentives for people to get around without relying on driving alone in a car.

 I hope the idea spreads. It is the way to have smart growth without having worse traffic congestion.

Here are references for the studies linked above:

• Chris McCahill, University of Wisconsin, et al.  "Effects of Parking Provision on Automobile Use in Cities: Inferring Causality" [PDF]
• Rachel Weinberger, University of Pennsylvania, "Death by a thousand curb-cuts: Evidence on the effect of minimum parking requirements on the choice to drive" [PDF]
• Jennifer Ziebarth, Tien -Tien Chan, Chris Mitchell, Fehr & Peers, "Parking Analysis and Methodology Memo - Final" [PDF]