Mark your calendars and plan your detours, folks. Starting May 15, both lanes of State Route 18 will be completely closed for a construction marathon that's set to last just over five days, right near the I-90 bridges. The reason? Crews will be hammering away at the southern portion of the lengthy-titled I-90/SR 18 Interchange Improvements project slated for completion this summer, according to a report provided by the Washington State Department of Transportation (WSDOT).
The clock will start ticking on the closure from 9 p.m. Thursday, May 15, rolling all the way through to the early morning of Wednesday, May 21. For those counting, that’s a full stop on traffic in both directions under the bridges. Strategically, the timing is chosen to avoid clashing with high-traffic weekends associated with Mother’s Day and Memorial Day, because nobody wants extra standstill memories with mom or in remembrance of those who served.
The game plan calls for new drainage and electrical works to be laid down, fresh pavement, and the construction of concrete islands—all essential to the diverging diamond interchange taking shape there. "The extended closure will eliminate the need for 10 consecutive nights of ramp and intersection closures," WSDOT explains, and is all about improving safety and keeping things on schedule.
But it isn't all shutdown and detour signs. Some routes will stay open to keep I-90 traffic moving, albeit with some restrictions. If you're cruising eastbound on I-90, forget about hanging a left onto eastbound SR 18—won't be allowed. Westbound off-rampers can't turn onto westbound SR 18 either. Instead, SR 18 traffic will be rerouted onto nearby detours—something to keep in mind to avoid surprise delays in your commute. And a friendly note from WSDOT for the truckers: big rigs should skip Issaquah city streets and stick to the highways proper.
Once SR 18 reopens on May 21, expect most of the southern interchange construction to be complete. Yet, more work will be happening under the I-90 bridges and at the northern end before traffic patterns can settle into their new diverging diamond dance later in the summer. This entire road ballet is part of a larger act that includes widening SR 18, building new wildlife-friendly bridges, and a separate bridge over Raging River to improve traffic flow and safety, as detailed by WSDOT’s announcement.
In the meantime, if you're making plans around the closure, your best bet is to stay tuned to real-time traffic apps or WSDOT's social channels for the latest on road conditions. This is a slice of info you’ll want to keep at your fingertips to navigate the near-week of roadworks with the minimum fuss. By the time the dust settles, SR 18's upgrade should be well worth any temporary inconveniences experienced during these dogged days of May.
