'Structurally deficient' bridge needs work, engineering report says

The Knudsen Drive bridge over the railroad tracks along Highway 99 was deemed "structurally deficient" by an engineer in its last inspection.

The bridge that takes Knudsen Drive over the railroad tracks just north of Norris Road is 70 years old and showing it.

County officials insist it is safe for travel despite an engineering report that lists it as "structurally deficient." County Engineering Manager Mark Evans takes the bridge about twice a week.

"I wouldn't if I wasn't confident in it," he said.

The Caltrans report, produced every two years after a careful inspection, recommends stripping the bridge deck and treating it with a chemical seal designed to keep water out of the concrete slab.

When water seeps into the concrete through small cracks, county officials say reinforcing steel gets wet.

"Water is never good for steel," Evans said, noting that in general the steel structure remains in good shape.

Evans believes a seal could be added to the bridge deck for about $20,000. The county will attempt to get state funding to have multiple bridges in need of the treatment done at the same time. That could happen by next spring, Evans said.

Another problem stems from the metal guardrail on the sides of the roadway. There's considerable spalling (cracking) throughout the concrete deck where the rails are attached.

"You've had chunks of concrete coming off the edge," he said. "That can be dangerous, especially where it's happening over the road."

County concrete crews will do patch work prioritizing the areas above traffic, but the work isn't on the calendar yet.

A third problem that presents considerably more of a challenge is the steel support columns. They are placed far too close to the road. Evans believes the bridge came first, but now high speed traffic runs just inches from the supports.

In the event a drowsy or distracted driver drifts off the road, how much force can the pillars withstand?

"The answer is, we don't want to find out," Evans said.

Traffic engineers are studying a possible solution to the problem. Evans envisions a barrier along the road that would be strong enough to keep vehicles away from the pillars, but soft enough to avoid bouncing them all the way back into oncoming traffic. Such a solution would carry a price tag in the tens of thousands, Evans said. He hopes to secure a federal grant for that.

Also on the to-do list for the county is fencing off the area beneath the bridge on the north hill. A homeless encampment there is preventing inspectors from properly evaluating the structure. It's a problem the county has run into at several bridges around town.

The vehicle guardrail on the hills ascending and descending the bridge are also badly in need of an upgrade, Evans said. Their smooth surface is well below industry standards now. That is expected to happen soon.

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