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Offering commentary and analysis from Washington, Oregon, and Idaho, The Cascadia Advocate is the Northwest Progressive Institute's unconventional perspective on world, national, and local politics.

Wednesday, August 7th, 2019

Big East Link milestone: Sound Transit’s light rail bridge over I-405 is structurally complete

Perceptive drivers stuck in gridlock on I-405 in Bellevue have probably noticed a new bridge being built above the interstate over the past year or so. What they may not know is that in just a few short years, trains will be zooming across that bridge as they carry passengers to and from downtown Bellevue.

Construction of East Link, Sound Transit’s big light rail extension that will connect Mercer Island, Bellevue, and Overlake with Downtown Seattle in 2023 and Redmond in 2024, is more than 55% complete.

This includes significant portions through Downtown Bellevue.

East Link will have three stations near the Bellevue downtown core:

  • East Main: south of Main Street on 112th Ave SE;
  • Bellevue Downtown: just east of the Bellevue Transit Center and south of the Meydenbauer Center; and
  • Wilburton: east of I-405, at the intersection of NE 8th St and 118th Ave NE.

To get light rail moving through Bellevue’s dense central business district with minimum surface-level disruption, Sound Transit contractors have dug a tunnel underneath the city, connecting East Main and Bellevue Downtown stations.

Bellevue Downtown north light rail tunnel portals

The Downtown Bellevue light rail north tunnel portals, seen from the I-405 light rail bridge (Photo: Andrew Villeneuve/Northwest Progressive Institute)

This is a sequentially excavated tunnel, where opposite-direction tracks run right next to each other – unlike the light rail tunnels in Seattle, where two separate tunnels carry trains in between stations on the underground alignments.

The big advantage of the approach utilized in Bellevue is a reduction in cost and risk: why dig two tunnels when you could dig just one? According to Sound Transit engineers, many lessons were learned from previous tunnel projects, including the infamous problems with Bertha, which dug the State Route 99 tunnel.

Improvements to technology mean that larger tunnels carrying two tracks can be dug reliably. In fact, the Bellevue tunnel was successfully excavated five months ahead of schedule – fantastic news for the on-time completion of East Link and a great factoid to share with friends and family who might not support NO on I-976 concerned about delays on big transit projects!

The Bellevue Downtown Link station is located right next to the existing transit center, connecting well to existing and future transit service. This includes the RapidRide B Line to Redmond, the I-405 Bus Rapid Transit corridor (future), as well as existing King County Metro and Sound Transit service. While touring the work site, NPI staff saw buses making frequent trips from the transit center – including this double-tall Route 535 bus headed to Lynnwood!

Northbound Sound Transit 535 Express

A double tall Sound Transit 535 Express bus leaves downtown Bellevue (Photo: Andrew Villeneuve/Northwest Progressive Institute)

East of Bellevue Downtown station, East Link rises above I-405 on a specially-constructed bridge sixty feet above mainline expressway traffic. Construction started with metal falsework (akin to an exoskeleton) going up above the interstate in early 2018 (link, page 19). Now, the bridge is complete, stretching from the tunnel portal to Wilburton station before descending to the ground.

The bridge is eight hundred and ten feet long, with a a three hundred and fifty foot span across I-405. It was cast-in-place, meaning that concrete was poured and solidified on the construction site, unlike the bridge spanning I-90 in south Bellevue, which is a balanced cantilever bridge.

The concrete bridge has been post-tensioned, making it able to withstand a “2,500 year event” – meaning that even in the case of rare natural disasters, light rail infrastructure will remain safe and usable.

The main span of the bridge is hollow, with fourteen-inch thick walls and ten-to-sixteen-inch thick horizontal slabs. Due to the cast-in-place nature of the structure, it was hand-built entirely by workers on-site, and all materials were U.S.-sourced.

View of Bellevue from I-405 East Link alignment

A view of downtown Bellevue from the new East Link light rail alignment, which will carry Blue Line trains across I-405 to and from the city center (Photo: Andrew Villeneuve/Northwest Progressive Institute)

Metal support structures were used to support the entire bridge as the deck and pillars were being filled out. Now that the bridge has been structurally completed, it is time for the external metal that currently stretches between the concrete bridge and active lanes of interstate traffic to be removed.

Moving to this phase of construction means that I-405 through Bellevue will have to be closed during parts of the next two weekends.

Southbound ramps will be closed the night of Friday, August 9th through Saturday, August 10. Southbound mainline traffic will then be closed from Sunday, August 11th at midnight until just before the morning commute on Monday, August 12th. Northbound ramps will be closed the night of Friday, August 16th through Saturday, August 17th. Likewise, northbound mainline lanes will be closed early Sunday morning until the morning commute on August 19th.

“During the weekend closures, crews will use an electric winch to remove and lower the heavy falsework to the road surface, where it will be completely disassembled and removed,” Sound Transit explained in an advisory about the work.

“Without the weekend directional closures, this complex process would have taken more than twenty weeks of weeknight work to complete,” the agency added.

Visit Bellevue’s city government website for detour information and Sound Transit’s website for more information on the closures.

Despite the closures, light rail will be coming to the Eastside in four short years. Once here, it will be here to stay, with light rail running every six minutes connecting Redmond and Bellevue to Seattle, Northgate, and Seatac for decades, even centuries, to come. It will revolutionize travel on the Eastside.

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One Comment

  1. Getting closer! It will be so cool when it’s finished and I can ride it.

    # by Catherine Hearn :: September 3rd, 2019 at 4:52 PM