The first of eight specially designed track connections for light rail is now in place on the I-90 bridge.
On Tuesday, Sound Transit gave reporters a close-up look at work to install tracks on the floating bridge, the first such project in the world.
Engineers had to design a special connection between the fixed section of the bridge and the floating section that goes up and down with the lake level.
"It's amazing, it's sort of Sound Transit's moon shot, which is an overused term this week, but it is, it's never been done before," said John Sleavin of Sound Transit.
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Sleavin said after extensive computer modeling, the agency brought trains to a testing facility in Colorado where the track connections were torqued to simulate any movement on the bridge.
Sleavin also explained how the tracks would respond if was a catastrophic failure of the Ballard Locks and Lake Washington drained up to 20 feet.
Sleavin said there's a fuse built into the tracks for that nightmare scenario, so they pull apart and don't hang up and damage the lowering bridge.
Preserving the floating bridge is crucial.
It's one reason the tracks are being glued onto the deck, instead of drilling 18,000 holes for rebar.
Sleavin said Sound Transit is "highly confident" in the glue. "We tested and double tested and triple tested all this."
Light rail service to 10 new stations on the Eastside is due to open in 2023.
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