Light rail across I-90 floating bridge will be first of its kind; closures of HOV lanes start June 3

SEATTLE -- Sound Transit’s $3.7 billion project connecting light rail to the Eastside over the I-90 bridge gets started June 1. The project is part of the East Link rail service that will create 14 miles of rail connecting the Eastside to Seattle, part of that stretch will mean trains traveling over the I-90 floating bridge.

An engineering feat, building a train structure over a floating bridge, something that’s never been done in the world.

Engineers say they’re using materials and design techniques that are proven and commonly used in the industry but in a unique way to handle this special concept.

“The commute’s getting worse for everybody, I’m seeing it on the 90 for sure,” said Brady Wright, who lives in Issaquah and commutes to downtown Seattle every day for work.

Wright has lived abroad, spending eight years in Australia and he said that public transit in the Northwest just hasn’t been efficient.

“Obviously the buses are OK, but they’re traffic dependent. If you’re stuck in traffic and you’re on a bus, you’re going to be in trouble there,” said Wright.

The commute congestion, the constant closures, “It absolutely affects you,” said Wright. He added that some days the biggest challenge is simply getting on the freeway from downtown.

“A lot of the issue is getting from where we are right now in downtown Seattle even onto the freeway can take 20 minutes, if not longer,” said Wright.

He said light rail across I-90 is something that can’t come soon enough.

“I think an opportunity to get light rail on a floating bridge that decreases traffic and congestion and gets you to where you need to go quicker, let’s do it,” said Wright.

Doing the project means doing something that’s never been done before.

“There is no light rail that’s on a floating bridge anywhere in the world,” said John Sleavin, the deputy executive director of technical oversight for Sound Transit.

The project is another first in Western Washington as more mega transportation projects continue as the Puget Sound region booms.

The mega project comes at a mega cost of $3.7 billion.

“That’s a lot of money, but the reality is people care about what’s affecting them on a day to day,” said Wright.

The project was approved by voters for the Sound Transit 2 measure, bringing 14 miles of rail to the Eastside, including across I-90, which would make for a 15-minute commute from Bellevue into downtown Seattle.

“It has been a very exciting thing to be working on,” said Sleavin, who is one of the engineers on the project. He said the unique challenge the project provides makes it more fun and interesting as an engineer.

“I’ve been working on this particular aspect for about six years,” said Sleavin.

The floating elements of the I-90 bridge made the engineering and design even more challenging.

“The bridge goes up and down, also when the wind blows the bridge will go slightly north or south, because it’s on anchor cables much like a boat will kind of move around. And, then as traffic loads, the bridge will also move a little left and right,” said Sleavin.

Engineers had to accommodate six degrees of motion.

The transition point between the fixed and floating structure of the bridge was a standout place to maneuver.

“Very similar if you’re walking from a fixed dock to a floating dock and you have that ramp that connects the two and it goes up and down with the tide,” said Sleavin.

At this transition, the rails will rest on bearings and plates allowing movement with the changing lake and bridge conditions. Sound Transit partnered with a company in Tacoma to build two full-size track bridges and test them under simulated operating conditions at a transportation technology center in Pueblo, Colorado.

Sound Transit said it passed all the critical tests.

Trains ran hundreds of times over the test tracks, mimicking the force and movement it’ll experience during normal operations at a speed of 55 mph.

“It’s weight, it’s balance, it’s trim, it’s basically, it’s a 3,500-foot-long boat we’re driving across,” said Sleavin.

Safety, a top priority for Sound Transit, but not much of a concern for Wright.

“Not one time have I thought of safety being an issue. I imagine the smart people that are getting it all done are going to make sure it’s nice and safe for us,” said Wright.

Sound Transit says in the rare event of a strong windstorm, with winds between 30 to 40 mph that generate strong waves, it could cause train service to be reduced.

“About once a year we may only allow one train per direction, and about once a decade we may have to cease operations on the bridge until the wind dies down,” said Sleavin.

Four car trains are projected to start running in 2023, “And those will be at 8 minute headways in the peak hours, each direction, so about every four minutes there will be a train crossing the I-90 bridge,” said Sleavin.

A daily ridership of 50,000 is expected by 2030.

“Not being with their families and not being able to do the things you want to do is a big issue, so if you can get an hour back, a half-hour back every day, that’s what people care about,” said Wright.