Tukwila’s steel Allentown Bridge, damaged by an over-height truck cargo in December, will reopen by April 1 but with only one lane, city leaders have decided.
The bridge’s dented beams were quickly restored to normal shape using heat torches, raising hopes that normal traffic on the two-lane span might return by February.
But in a follow-up analysis, engineers worried about a damaged gusset plate, shaped like the armor on a stegosaurus, where three beams converge near the deck. Rivets that connect the plate and beams were feared to be permanently weakened when a vertical beam was yanked inward during the crash Dec. 15.
“There’s really no way of knowing if the steel rivets have been compromised, without taking apart the whole bridge,” Rachel Bianchi, deputy city administrator, told the Tukwila City Council on Monday night. That crucial plate is wedged between the deck and walkway of the bridge, providing no clearance to replace the rivets.
This complication helps explain why Tukwila officials took nine weeks to choose and reveal a reopening plan, since the contractor straightened a dented overhead brace and side beam Dec. 28. The city’s plan still requires state approval.
Once the bridge reopens, the single lane will flow southbound, and will be centered to distribute weight evenly.
A one-lane strategy reduces potential traffic weight by half, said Bianchi. The span carries up to 3,000 trucks per day, primarily serving a huge BNSF Railway container terminal, and 7,000 cars.
The lane reduction is expected to last until 2025, the city’s target date to build a replacement at or near the same spot, for $22 million to $26 million, said Adam Cox, city transportation project manager.
The 73-year-old truss bridge across the Duwamish River was already deemed structurally deficient in the National Bridge Inventory, because of a crumbling concrete foundation. Its sufficiency rating, which combines traffic capacity, structural quality, safety and waterway clearance, scores 6 on a national scale of 100 points, and will be lowered further, an engineering update says.
Residents of the riverside Allentown neighborhood favored northbound traffic, and new Councilmember Mohamed Abdi, raised questions about how long it takes to switch directions, if southbound doesn’t serve the community. Such a changeover normally requires six months, to give public notice and adjust drivers’ habits, staff replied.
Tukwila officials say southbound is the quickest layout for firetrucks leaving Allentown. In addition, it’s the safest direction to serve residents who drive out toward Southcenter, because of a nearby stoplight, Cox said. Otherwise, they’d be taking side roads farther north, and turning left without signal help, into busy East Marginal Way South.
Sally Blake, co-founder of the Allentown Advocates neighbor group, argues northbound is safer because if the bridge lane flows south, lineups of three semis will strain and clog the old span while waiting for a green traffic light at Interurban Avenue South, going toward Highway 599.
Tukwila can re-time that signal, giving more priority to bridge traffic leaving Allentown, city staff said.
However, the city’s plan will prolong the hazardous detour route established in December, where trucks arriving to the BNSF Railway yard descend from hilly Skyway across I-5 into lowland Allentown. (That bridge sits partly on charred wood timbers, yet multiple semis cross at the same time.)
“They’re coming down really fast, bottoming out at the bottom of the hill, causing road damage and speeding, in an area where there are homes and driveways and pedestrians, making it from our perspective a far more unsafe set of conditions,” said Allentown resident Mary Fertakis. It would be safer if trucks arrive using the steel bridge northbound, and leave the neighborhood at lower speeds, heading uphill toward Skyway, she said.
Last fall, the City Council budgeted $1.3 million to study a second railway-access bridge or trucking road that’s farther from houses and the community center.
Meanwhile, neighbors in Allentown have asked for speed bumps.
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