NPI's Cascadia Advocate

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