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The damaged steel plate on Interstate 5 that ruined the Thursday morning commute is an outdated piece crews have been replacing on other Seattle freeway decks. But the state lacks maintenance money to improve the whole corridor.

The 5:50 a.m. incident, near South Holgate Street in Sodo, triggered southbound backups of 10 miles. A drive from Lynnwood to Southcenter took two hours.

A dangling chain on a truck somehow caught the steel plate and yanked it upward, says the Washington State Department of Transportation (WSDOT). Three vehicles were reportedly damaged, and three of the five freeway lanes were closed.

The truck driver called to report the chain as a likely cause, according to agency spokesman Bart Treece.

The accident can’t be blamed on lapses in maintenance or inspections, Treece said. “It’s probably not something you’d be likely to see again.” The area is inspected every few weeks, state officials said.

However, the threat of aging steel plates wouldn’t exist at all, if the state could replace them with new-generation rubber or silicone fillings.

“They come up, with the vibrations. That’s an old design; they were designed in the 1960s. That’s why we do away with the sliding plate,” said Sam Al Mallah, a WSDOT engineer.

An expansion joint is a gap between bridge spans, allowing the structures to expand and contract with temperature changes. Many are covered by steel plates to protect the joint from moisture or erosion. The long plates are ¾-inch thick, and it typically takes two strips to cross a five-lane highway.

A leading theory Thursday was that the truck’s chain snagged a corner where two strips meet, uprooting 10 to 12 feet of one strip. Another possibility is the chain caught the head of a 1½-inch-wide bolt that holds down the steel. The bridge team may never know for certain, said Treece.

The freeway reopened five hours later. To accomplish this, a state bridge crew heated the steel plate to soften it, then drove over it with trucks to push it flat, then bolted it to the road deck, before the afternoon commute.

Just like pavement ruts and rusting bridges, steel deck plates are a symptom of gradual decline. As far back as 2008, then-WSDOT Secretary Paula Hammond said it would require $2 billion to redeck I-5 through Seattle but delayed asking for the money because of political realities.

Damaged joints are a known hazard on the Seattle freeway, which opened in 1965.

“They’re aging. They’ve served us well. They’re serving their purpose,” said Lorena Eng, WSDOT regional administrator. “Unfortunately because they are old, they’re like anything that’s wearing out.”

Most of the state’s gas tax goes to pay construction costs for highway projects, including the Highway 99 tunnel, 520 bridge, Snoqualmie Pass East and I-405 widenings. Lawmakers spent the last few years talking about but not agreeing on a multibillion-dollar package of road widenings and extensions, as maintenance funds run low.

Meanwhile, repairs proceed gradually on I-5. In 2007, the state replaced steel plates with rubber joints in the northbound lanes near downtown. That’s one of three new-generation joint designs the state is using to replace steel coverings on I-5; the others involve filling the gap with compressible silicone. All three methods avoid setting steel parts on the driving surface.

A $12.3 million program is under way that included joint replacements downtown and on ramps near Beacon Hill. The weekends of June 6-9 and 27-30, state contractors will replace joints on northbound I-5 near the West Seattle Bridge exit. In July, two expansion joints on westbound I-90, on the West Channel Bridge from Bellevue to Mercer Island, will be replaced.

Eng said 27 of 33 targeted I-5 joints were replaced in 2013-14. But the site of Thursday’s failure isn’t on the 2014 work list. It hasn’t been a big problem in the past, she said.

This reporter saw a different joint plate spring upward nearly three feet on May 17, in the right lane of southbound I-5 near King Street, when a tanker truck rolled through the center lane. The cover snapped back into place.

WSDOT suggested Thursday that motorists who see such hazards call 911.

During routine inspections, Eng said. Workers listen from beneath for unusual noises as tires roll over the joints, and can inspect further when needed.

Eng said that during the northbound project seven years ago, the state also repaired and refastened its southbound joint covers, including in the Sodo area.

“We hoped that project would buy us more time, but that was back in 2007,” she said. Eng noted that joint replacements require lane closures, a significant challenge.

A motorist passing the spot Thursday morning, Adrian Atman, says he felt a jolt
to his Honda, then learned through news accounts it was a broken expansion joint.

“I was right next to a semi with two trailers. It looked like a fuel truck,” he said. “I heard this extremely loud bang, and my car lurched, like I had just been hit.”

“I thought some debris had struck my vehicle,” he recalled.

After impact, he slowed from 65 mph to 55 mph and took the Albro-Swift exit. He arrived at work and noticed a bulge on the outside of the right rear tire. Atman said he would have a mechanic check for damage to the suspension.

He said he recently sold his motorcycle, avoiding a potential tragedy had the joint break occurred while he was on two wheels.

“No place … to go”

Thousands of motorists detoured but found congestion on I-405, Highway 99 and arterials.

Traffic signals in the city gave north-south travelers extra green-light time throughout the morning, said Rick Sheridan, Seattle Department of Transportation (SDOT) spokesman. The Fremont Bridge opened for boats at 9:30 a.m., but for the city to
keep the drawspans down at that hour requires advance permission from the Coast Guard.

Sheridan said SDOT’s software automatically adds green-light time based on conditions on Aurora Avenue North, Elliott Avenue West, 15th Avenue Northwest and First Avenue South. For instance, he said the north-south green time on Elliott swelled Thursday from 110 seconds at 6 a.m., to 140 seconds at 6:49 a.m. and 180 seconds (three minutes) by 7:39 a.m. — staying there until dropping back to 140 seconds at 11:09 a.m.

“There was virtually no place for vehicles to go, because so many were detouring off the road,” Sheridan said.

And the state bridge crew’s late-morning fix couldn’t save the afternoon commute. The residue of congestion, mixed with a vice-presidential visit and a crash near Southcenter, caused more delays and overdue transit arrivals.

Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom