2020 update: here are selected rides starting at the I-90 bridge East Tunnel viewpoint
It’s a lot harder to ride east along the I-90 corridor than it should be. If you’re leaving, say, the waterfront trail you have to navigate city streets to Dearborn where you pick up the bike lane under I-5. the I-90 trail takes you through the parks on the cap over I-90 and then through a pedestrian tunnel over to the lake. There is a steep descent to lake level (and a connection with the Lake Washington Loop) and then a ride across the bridge. On Mercer Island you can stick with the trail along the freeway or you can peel off and ride parallel streets. The bike lane on the bridge across the east channel is narrower and there is a hairpin turn where it ends at Enatai Beach. You go under I-90 a couple of times and end up back on the north side riding planchon across the Mercer slough. At the east side of the slough you connect with the other side of the Lake Washington Loop and you have to know where to look to find the continuation of the I-90 trail to Factoria. That continuation gets you through the I-405 interchange and puts you out on the South side of I-90. Then you need to take surface streets up to Eastgate and get across the freeway to pick up the next segment of the trail. There is a pedestrian overpass at the top of the hill on 36th (just before the intersection with 150th – signed for Korean BBQ) which puts you out on Eastgate Way. The entrance to the trail is off Eastgate Way east of the interchange and is not totally obvious. Alternatively you can stay on 36th and cross 150th. Sneak through the parking lots and exit onto SE 37th to find an underpass with a wide sidewalk. Hang the first right after the underpass and you’ll run right into the trail entrance.
For another option, you can turn right onto 150th and after a couple of blocks uphill make a left onto Newport Way which gives you access to the pedestrian bridge over to the trail or takes you all the way into Issaquah. To get to Newport Way with less traffic than 150th, you can continue on 36th straight across 150th where it changes into 38th, take the first left uphill (154th), jog right on 39th to get to 153rd and take that up to Newport Way , the pedestrian bridge, etc. (heading west this has an official bike route sign off of Newport Way.)
The I-90 trail east of Eastgate is wedged between people’s back yard hedges and the interstate. It passes under a pedestrian bridge – the spiral to access that bridge from the trail would be a challenge to ride – and goes down several switchbacks with turns so steep you pretty much have to dabble to get around them. At the bottom it emerges at the back of the staff parking area of an elementary school in a well camouflaged trailhead.
You’re immediately thrown into the West Lake Sammamish Way traffic circle. You want to ride 3/4th of the way around and head east. The road is narrow but doesn’t have much traffic. You have to make a left at the Freeway on ramp (SR 900 – Lake Sammamish State Park) to stay on NW Sammamish Rd. At Lake Sammamish Parkway you can pick up the new East Lake Sammamish trail, or you can cross the road and find your way to the new access to the High Point Trail.
Here is a link to Jim Carson’s write-up on the route.
Here is a link to his discussion about alternatives for getting to and from the Sammamish Plateau.