Issaquah presents early options for Central I-90 multimodal crossing; staff will pursue outreach

City public works staff on Aug. 5 gave an informational update on a study to create a Central Issaquah multimodal crossing of I-90 intended to improve north-south mobility, support anticipated growth in the regional growth center and align with a future light-rail station. The study team advanced five crossing alternatives for further refinement and outreach after screening for feasibility.

The update, led by senior engineer Greg Lucas and public works director Emily Moon, said the study is funded through the American Rescue Plan Act and that a multidisciplinary consultant team led by Jacobs is under contract. The proposed crossing concept would typically include a three-lane roadway with sidewalks and protected bike lanes; staff said the crossing must be compatible with the city's mobility master plan and the future street grid in Central Issaquah.

Key constraints: Lucas flagged several technical hurdles that eliminated some early options, including a high water table and geotechnical challenges in lakebed soils that made many undercrossing alternatives impractical, drainage complexities, and limited elevation differences at Gilman Boulevard and adjacent streets that constrain how the crossing could be graded. Some overcrossing options would require lowering or raising portions of I-90 or Gilman Boulevard, which increases complexity and potential impacts to existing properties and future development parcels.

Alternatives and trade-offs: Staff described multiple overcrossing alignments and one undercrossing that currently appears feasible in concept. Trade-offs include construction footprint, property impacts, effects on local circulation, visual/height impacts, and opportunities to tie the crossing into future development parcels and the potential light-rail station. Staff emphasized the need to avoid designs that create new local traffic bottlenecks.

Council questions and community process: Council members asked about parcel impacts, how the crossing would tie into future development and a light-rail station, the evaluation criteria and performance metrics the team will use, and whether the study could minimize impacts to existing businesses. Staff said they will develop performance metrics tied to goals, continue outreach to property owners and boards/commissions, launch an online questionnaire and hold open-house events later this summer, and refine alternatives with WSDOT and Sound Transit input.

Next steps: No action was requested. Staff will continue technical analysis, outreach to property owners and stakeholders, and will return with refined alternatives and performance measures for additional public review and board/commission input.