Yes, Seattle’s Lower Spokane Street Bridge is cracking too
The Lower Spokane Street Bridge is cracking, but it’s not quite time to panic yet, according to the Seattle Department of Transportation.
These are not new cracks, nor are they unusual. These are the type of cracks you find in every concrete bridge structure. They crack by design — it’s the way they handle the stresses of carrying loads.
SDOT’s Ethan Bergerson said engineers have been watching these cracks for a while, inspecting them monthly since they were discovered.
“We’ve taken a close look at the cracks, which we have known about for a while, on the low West Seattle bridge, and we found that they are nothing like the cracks that are on the high bridge,” he said.
The high bridge cracks are atypical. The cracks on the low bridge are what engineers would expect to find after 28 years of hard work.
That said, Bergerson said the city is at a decision point on the lower bridge.
“The bridge is in a condition that we need to either make investments in repairs or the federal guidelines would allow us to address that with load restrictions,” he said.
There will not be any significant load restrictions put on the bridge because the city is going forward with repairs. It has already repaired the cylinders in the swinging mechanism, and has repaired the pedestrian gates. It has also has already done some paving.
Over the next year and a half, the city will repair the locking mechanism and wrap the structure in carbon fiber, just like it is doing with the high bridge, but only as a precaution. The city will also reduce the speed limit from 30 to 25 miles an hour to help reduce the vibrations from large vehicles like buses, fire trucks, and semis.
“A large truck going over the bridge causes vibrations that causes long-term stress on the bridge, and making sure that those trucks are moving at 25 miles per hour makes a big impact for long-term stability,” Bergerson said.
The city is also going to install photo enforcement on the bridge to make sure everyone is following the current restrictions on the lower bridge, which makes it off-limits to anyone but transit, emergency vehicles, and freight during the day. The city’s plan to add about 160 vehicles an hour in each direction, as they expand the list of those that can use the bridge during the day, can still be accommodated.
Bergerson said the city is doing everything it can to give this bridge the TLC it needs.
“The West Seattle low bridge plays a critical role in our transportation system,” he said. “It’s a small but mighty bridge. After years of being over shadowed by the high bridge, it is now one of the most important bridges in the city.”
SDOT doesn’t know how much it will cost to make these repairs, or what kind of closures will be necessary. The same high-tech equipment monitoring the high bridge is also being used to check the lower bridge.
Thankfully, the cracks on the lower bridge are not expanding like those on the upper bridge.