Most studies that employ this method of assessing parking requirements find that minimum parking standards constrain development in big cities. But these studies are limited by being counterfactual estimates: We are guessing what would have happened under different zoning. It is preferable to have an actual zoning regulatory change occur, and then observe what happens. Seattle offers an opportunity to do that.
Seattle’s Parking Policy Reforms
In 2012, concerns about housing scarcity led Seattle to lower its parking minimum requirements. Doing so was in line with the city’s comprehensive plan, and with regional plans that emphasized connecting denser growth centers with more public transit options. Before this reform, Seattle had required residential developments across the city — except for downtown and some special housing types — to provide at least one parking space per housing unit. The 2012 reforms changed this requirement in three big ways. First, the city eliminated all off-street parking requirements for multifamily housing in neighborhoods the city considered “high-density urban centers” (e.g., downtown Seattle, Capitol Hill, South Lake Union, Uptown, and the neighborhoods around the University of Washington). Second, it eliminated multifamily parking requirements in residential and non-residential uses in “medium-density neighborhood centers” (or “urban villages”) located within a one-quarter mile of a public transit stop that ran at least every 15 minutes for most of the day. Third, the city reduced parking minimums by 50% along major transit corridors outside these areas, as long as they were within a one-quarter-mile walk of transit stops with frequent service.
In essence, the reforms created three new types of what we call “parking zones” — areas with particular parking requirements. The new parking zones gave us places to observe newly deregulated housing projects and see if developers built less parking. For our analysis, we collected data on all of the 868 residential and mixed-use developments that required a “master use permit” that were approved from June 2012 to October 2017 — this included nearly all of the multifamily and mixed-use developments approved during this period in the city. These projects involved 60,361 housing units and 39,350 associated parking spaces. For each project, we collected data on the number of housing units, the minimum parking required, and the number of spaces developers actually built. We also included data on transit accessibility and other neighborhood characteristics, to control for factors beyond zoning that might influence the provision of parking.
Quantifying Effects of Parking Requirements
The parking zones, and the projects we studied, are shown in Figure 1. The brown and yellow shaded areas are the zones, the dots indicate housing projects that were part of the study, and the colors indicate the ratio of housing units to the number of parking spaces actually built. We also show some special housing types, including affordable housing, that were subject to lower parking requirements.
Figure 1: Seattle residential developments in study (2012-2017), with actual and baseline required parking spaces per unit
The overarching takeaway is that Seattle’s parking reforms significantly reduced parking supply in new buildings. About two-thirds of the projects we examined — mainly those in the downtown and its densest surrounding urban centers — were not required to provide any off-street parking. Most buildings in our sample provided less than one parking space per unit, and a sizable share, nearly 20%, provided no parking at all. Table 1 shows the distribution of actual parking provided per housing unit post-reforms broken down by minimum parking standard (0, 0.5, and 1 space per housing unit). The average building in areas with reduced parking requirements had 0.91 spaces per unit while those in areas with no parking requirements had 0.49 spaces per unit. Lastly, all but one of the 868 developments had less than two parking spaces per unit, a standard that is common (and sometimes required) in other cities.
Most developers closely adhered to the minimum parking requirements. About 34% of the developments included the exact amount of minimum parking required in the code; nearly 30% of the buildings in areas where no parking was required took full advantage of the revised standard (70% provided some parking even here). Demonstrating the effect of the reforms, nearly 88% of buildings in areas where 0.5 spaces per unit were required included less parking than required under the pre-reform standards. In areas where one parking space per unit was required, more than two-thirds of developments included exactly one space per unit, while only one-third exceeded that minimum standard.
When developers did exceed the minimum, they rarely did so by more than one-half space per unit. This was particularly true in areas where the city required 0.5 parking spaces per unit; here, more than three-quarters of developers built between 0.5 and one parking spaces per unit. Overall, about two-thirds of approved projects provided more off-street parking than required by the parking regulations, which suggests that the developers felt the market demanded at least some additional parking. Nevertheless, the revised regulations led to developers supplying fewer spaces than they would have had to under the old regulations.
Table 1: Relationship between minimum parking required and parking provided in Seattle multifamily developments, 2012-2017
Our analysis demonstrates the sizable impact of the reforms, which in turn suggests the strong role that minimum parking requirements play in development decisions. In the urban centers, urban villages, and transit-oriented locations, developers built 40% less parking than would otherwise have been required. This reduction translates into almost 18,000 fewer parking spaces across 26,300 units. Assuming each parking space would have cost $30,000 to build, the reform saved $537 million in direct construction costs over five years — more than $20,000 per unit — a savings that likely benefited both housing developers and consumers alike. This figure does not include the opportunity costs associated with having to build parking in spaces that instead could be used for additional housing, as we discuss below.
Multiple factors — not just zoning requirements — influence the number of parking spaces a building provides, so parking reform has different impacts on different kinds of buildings in different areas. A statistical analysis of the data showed that while the parking requirement is the most important predictor of off-street parking, some types of high-end projects still build a lot of parking. This result suggests that developers think high-end developments need ample, or at least enough, parking to be competitive. All else equal, developments in areas with higher land values, and presumably more expensive units, had more parking per unit than others. Mixed-use developments also included more parking than residential developments, to satisfy the parking needs of offices and retail customers.