SNOHOMISH — Rick Lescher, of Snohomish, wrote in about what’s become a source of angst for Street Smarts readers: “Was wondering why one of the expansion joint gap covers has been missing for seems like around two years now on westbound Highway 2 near the Pilchuck River crossing?”

This column has fielded two other closely related questions in the past year, including one we printed a response for back in February.

This westbound approach to the Pilchuck River bridge has, indeed, turned out to be a bit of a problem spot.

“WSDOT has had to repair the U.S. 2 Pilchuck River Bridge expansion joints a couple of times the past few years,” spokesman Tom Pearce said.

The twist this time is that it’s the fix that drivers think is broken.

Let’s back up a bit.

Expansion joints allow bridges to flex with changing traffic volumes and weather. To drivers, they often appear as small gaps in the roadway. There are lots of parts, which means there’s plenty that can go wrong or wear out over time.

Replacing expansion joints can involve time-consuming closures, as was the case on I-5 in 2016 when WSDOT replaced expansion joints over Ebey and Steamboat sloughs — dubbed “the worst of the worst” at the time.

More often, it’s maintenance and small fixes along the way.

Enter our problem spot.

Cover plates were used to reinforce and span the expansion joint gaps at the east and west ends of the U.S. 2 Pilchuck River bridge. But the plates kept failing to hold westbound at the east end.

So WSDOT crews removed most of the plates, in stages, over the westbound lane. (One plate that covers the center of the roadway still extends a bit into the lane.)

Instead of cover plates, the expansion joint in the westbound lane at that spot is now reinforced with concrete-type headers. (For armchair engineers: Both types “provide a rigid lateral support to the expansion joint device and serve as a transition between the [hot mix asphalt] overlay material and the expansion joint itself,” according to the state bridge design manual.)

“The new concrete joint is just as safe and effective as the old one,” Pearce said.

It’s also the more common treatment for expansion joints statewide, and especially in Snohomish County.

“Most joints are concrete headers,” Pearce said. “I can say that in this part of Snohomish County this is the only bridge with cover plates.”

Inside the gap itself is a “flexible rubber gland.” This seal is placed below the surface of the road to avoid damage from passing vehicles.

For what it’s worth, there’s a slight bump as you drive over either type of expansion joint on that bridge.

It’s hard to say why this particular spot has had so many repair needs.

“It may have something to do with the approach that is on a curve to the left at that point. It could be due to the weight of traffic going in that direction, like log trucks and semi-trucks,” Pearce said. “It could also be the cover plate at that joint may have become fatigued, cracked and then just failed.”

As for further improvements, the road surface is scheduled to be repaved in 2019.

The bridge itself is in good shape. The Pilchuck River Bridge was built in 1983 and has a sufficiency rating of 84.73 out of 100.

Melissa Slager: streetsmarts@heraldnet.com; 425-339-3432.