UPDATE 9-21: The trail will remain open during the September 23–26 work.
WSDOT sent out an alert today that the trail across the I-90 Bridge will be closed most of Friday and all weekend as crews work on an expansion joint on the Homer Hadley Bridge, the wider of the two parallel I-90 floating bridges.
The trail will be closed starting at 10 a.m. Friday (September 16), so you will need a different way to get home in the evening if you bike across it in the morning.
People biking and walking will need to route either around the lake or to the 520 Bridge. There is no official detour route, though the Lake Washington Loop is a popular option (Cascade Bicycle Club has created a map for reference). There is also a popular route through Bellevue and Medina that sticks closer to the water. If you ever need to detour along an unfamiliar route, you can find popular routes by checking out the Strava and Ride With GPS heatmaps. Just note that both these routes between the bridges require riding in mixed traffic.
Details from WSDOT:
Sept. 16-19 closure
The first weekend’s work requires crews to close the West Mercer Way on-ramp to westbound I–90. People on Mercer Island still will be able to get onto westbound I–90 via the East Mercer Way and North Mercer Way on-ramps.
In addition to closing the West Mercer Way on-ramp on Friday, contractor crews also will close the right lane of westbound I–90. The right half of the expansion joint runs across the right lane through the on-ramp and across the bike path, which also will be closed for the weekend.
Sept. 23-26 full closure – two lanes closes Sept. 22
This closure actually will start with westbound I–90 reducing to one lane on Mercer Island at 2 p.m. Thursday, Sept. 22. All lanes will then close at 10 a.m. Friday, Sept. 23 (the on-ramp from West Mercer Way will remain open to westbound I–90.) All lanes will reopen by 5 a.m. Monday, Sept. 26.