What the Transit-Oriented Development Bill Means for Mercer Island

In 2025, the Washington State Legislature adopted House Bill (HB) 1491 (known as the “TOD Bill”), which established requirements for local jurisdictions to plan for transit-oriented development (TOD) in areas within a half-mile walk of any light rail station, also referred to as a “station area.” (see map below). HB 1491 was designed to encourage mid-rise development within the station area to promote access to mass public transit through increased density, affordable housing, and walkability. Mercer Island is required to adopt regulations to comply with HB 1491 by December 31, 2029. If the City does not comply by the deadline, then the regulations in HB 1491 supersede the City's existing development code.

A map of the half-mile walkshed from the light rail station.

Overview of HB 1491 Requirements

Under HB 1491, cities with light rail stations must designate all lots fully or partially within one-half mile walking distance of the entrance to the light rail station as a station area (RCW 36.70A.030(32)). Within the designated station area, cities are required to:

Allow an average of 3.5 floor area ratio (FAR), approximately between 4 to 8 stories, across the entire station area. Some areas may have a reduced FAR provided other areas have a greater FAR and the average allowed is not less than 3.5;
Require that a minimum of 10% of all units must be affordable (at 60% of the Average Median Income (AMI) for rental housing and 80% of the AMI for owner-occupied housing);
Grant an additional 1.5 FAR for developments that have 100% of units as either permanent supportive housing (units affordable at 0-30% of the AMI) or workforce housing (affordable at 80% of the AMI); and,
Allow multifamily residential and mixed-use development.
Reduce on-site parking requirements in residential or mixed used development.

The City is allowed to designate a modified station area, subject to review and approval by the Washington State Department of Commerce (RCW 36.70A.840). Some areas may be exempted from the station area, such as the shoreline jurisdiction, critical areas, and parks. The City Council will be providing further direction on the boundary of a modified station area in the coming weeks.