About the Calculator

What does it do?

The King County Right Size Parking Calculator lets users estimate parking use in the context of a specific site, based on a model using current local data of actual parking use correlated with factors related to the building, its occupants, and its surroundings—particularly transit, population and job concentrations. The calculator can help analysts, planners, developers, and community members weigh factors that will affect parking use at multi-family housing sites. It will help them consider how much parking is “just enough” when making economic, regulatory, and community decisions about development.

The calculator’s estimates are based on a model developed from field work data on parking utilization collected in 75 building in 2017, in addition to the 208 buildings collected in the winter and spring of 2012 on over 200 developments in urban and suburban localities in King County, Washington (Seattle and its suburbs). The calculator estimates a parking/unit ratio for an average residential building based on the characteristics of each location. A user can create scenarios for a parcel based on seven variables (see Background for more detail).

Why parking matters

The supply and use of parking are influenced by—and have influences on—development practices, local policies, economic impacts on builders and households, and community goals. The supply and price of parking also have direct relationships with travel behavior. Too much parking at residential properties correlates with more automobile ownership, more vehicle miles traveled, more congestion, and higher housing costs. In addition, excess parking presents barriers to smart growth and efficient transit service.

Parking supply and pricing often have a direct impact on the ability to create compact, healthy communities. King County Metro Transit has an interest in encouraging land uses, policies, and development that lead to communities that can be served efficiently and effectively by transit. Locally credible and context-sensitive data on parking use allows jurisdictions in King County to:

• Support economic development by reducing barriers to building multifamily residential developments in urban centers near quality transit infrastructure.
• Reduce housing costs as well as household monthly expenditures, allowing a larger demographic to participate in the urban, infill housing market.
• Encourage transit use, ridesharing, biking, and walking.
• Reduce traffic congestion, vehicle miles traveled, and the amount of greenhouse gases produced.

Who’s Involved?

This calculator was developed as a part of King County Metro Transit’s Right Size Parking Project, which is funded with a grant from the Federal Highway Administration’s Value Pricing Program. Partners include the Center for Neighborhood Technology, who constructed the statistical model and developed the website tool, and the Urban Land Institute, Northwest Chapter, who provided community engagement and outreach support throughout the project. For more information on the project, see the King County Right Size Parking website.