Mercer Island planners outline station-area zoning changes under state TOD law, warn of large infrastructure cost gaps

Mercer Island -- City staff briefed the Mercer Island School District board on the implications of the Growth Management Act and recent state housing laws, including House Bill 1220 (affordable-housing targets) and 2025's House Bill 1491 (transit-oriented development requirements around light-rail stations).

"My name is Jesse Bonham, the city manager for the City of Mercer Island," the city manager said as he introduced the briefing, which focused on the planning work required to comply with a Growth Management Board order and the new state TOD provisions. (Jesse Bonham, City Manager)

Jeff Thomas, the city's planning director, walked the board through a two-phase station-area boundary around the new light-rail station and explained key policy levers in HB 1491: allowing multifamily residential and mixed uses in station areas, reduced parking minimums, and average floor-area-ratio requirements that translate roughly to a mid-rise scale across the TOD footprint.

Thomas told the board that Phase One (which includes the current town center and immediately adjacent multifamily zones) must be adopted and in place by July 31, 2026, to meet the Growth Management Board and HB 1220 compliance obligations; Phase Two, which would address remaining single-family areas relevant to HB 1491, is due by the end of 2029. "Phase One work needs to wrap up by July 31st, 2026," Thomas said. (Jeff Thomas, Planning Director)

Staff presented capacity estimates: the city's land-capacity analysis showed a baseline of 1,558 units at the end of 2024; state statutory changes and earlier zoning updates added roughly 576 units in mid-2025; Phase One station-area implementation is projected to add about 1,031 units; and a full Phase Two implementation through 2029 could increase capacity by several thousand units, producing a range of roughly 6,200 to 8,200 units in the planning horizon. Thomas noted that those numbers reflect planning capacity only, not predicted construction.

City staff also emphasized infrastructure and funding challenges. "The city does not have the money to obviously do all that," Bonham said, adding that infrastructure needs for water, sewer, roads and capital facilities to support increased density could reach "hundreds of millions" of dollars and will require a mix of local, regional and state funding. (Jesse Bonham, City Manager)

Board members noted the potential impacts on district planning, school capacity and transportation; city staff said they will coordinate with the school district as planning proceeds and will return with more detailed timelines and analyses.

The presentation clarified deadlines and programmatic requirements the city must incorporate into its comprehensive plan and development regulations to meet state law and the Growth Management Board order.