When a new building is constructed, it is required to provide a minimum number of parking spaces. This number may vary, depending on how close it is to public transit, whether it contains affordable housing units, etc. In 2018, the City's parking requirements were eased, but they still remain a significant cost, and drive up both car usage and rents for all residents. Less parking will make for more walkable neighborhoods. For housing and office space that is near public transit, and particularly for affordable housing, it is not at all clear that parking minimums are serving a public good.
Current City Programs
Seattle's parking requirements are described here.