FOLLOWUP: SDOT explains why the West Seattle low bridge got stuck for 2+ hours

| Transportation | West Seattle news

(Monday night image from SDOT camera, via X/Twitter)

Monday evening, after reader tips (thank you!), we reported on the West Seattle low bridge being unusable to all surface traffic for two-plus hours. SDOT promised a followup explanation, and here it is:

The Spokane Street Bridge (also known as the West Seattle Low Bridge) was stuck from approximately 5:30 – 8:00 pm on June 24 due to a technical issue with the bridge’s tail locking mechanism.

The tail lock is the equipment that locks the bridge in place so that cars, bikes, and people can safely travel across it (it is called a “tail lock” because it is located where the two sides of the movable bridge meet in the center of the waterway, referred to as the “tail span” of the bridge). A specialized maintenance crew was called in to help diagnose and fix the problem and determined that the issue was likely caused by the bridge spans drifting slightly during the raising and lowering process, causing sensors to detect a misalignment in the locking mechanism.

We are currently working on a series of projects to maintain and modernize the Spokane Street Bridge. This includes a variety of investments to repair or replace the bridge’s control system, electronics, and mechanical parts. While much of this work has already been completed, there are ongoing plans for more repairs to address the bridge’s tail locking mechanism and other related parts.

Our moveable bridges operate with complex mechanical and electrical equipment. Though they are rare, issues with these systems can happen. When an outage occurs, our roadway structures crew and engineers work as fast as possible to restore service to the traveling public. A detailed explanation of our standard procedures to respond to bridge malfunctions is available on this webpage.

Admiral-2009 June 25, 2024 (2:34 pm)

How did the City deal with bike/pedestrian traffic during the closure?

reed June 25, 2024 (3:26 pm)

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I sucked it up and did the ~ 6 mile bike detour to the south over the 1st Ave bridge. Taking advantage of the beautiful day, I took the longer way home by blasting right up Highland Park Way and riding around through Lincoln Park to Beach Drive back to Genesee.

Neighbor June 25, 2024 (2:44 pm)

Though they are rare, issues with these systems can happen.Are they rare though? Seems like the low bridge breaks several times a year. What is SDOT’s definition of rare?

Alex June 25, 2024 (9:59 pm)

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A couple times a year would be like 0.1% of the times it opens. I would call that okay (but not amazing) for a one-off design movable bridge (literally there are no others like it) that’s older than I am and beaten by heavy trucks all day long.
- Neighbor June 25, 2024 (10:42 pm)
  
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  One failure out of a thousand times is extremely poor. 99.9% uptime is ten hours a year. We don’t tolerate that from our refrigerators. I’m not sure why we should tolerate it from our critical infrastructure either. You are right, it is the most reliable bridge of its kind. But then it’s also the least reliable. We can’t go back in time and choose a reliable, proven design but hopefully we take this lesson forward in future bridge construction.

Derek June 25, 2024 (5:17 pm)

Of course this happens on a day I decide to bike to work. RIDICULOUS!

Question Authority June 25, 2024 (5:42 pm)

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When you suffer from a flat tire on your bicycle do you blame the manufacturer, or do you except it as a random unavoidable failure beyond your control? It’s fruitless to complain about an unforseen random event on a complex electro-mechanical system, much bigger and more important than your inner tube, or your time.
- Jort June 26, 2024 (12:32 am)
  
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  ?????? Unlike, say, a broken bridge, I can fix my flat tires … and I don’t blame anybody??? The bridge being out of service is not a “random, unavoidable failure,” it may be random, and it is a failure, but its closures certainly can be avoided through mitigation, or responded to more urgently. Were you this sanguine about SDOT failures when the High Bridge was out of service for 2 years? Who’s comparing an infrastructure failure to an innertube?! Huh?!? I really don’t get this. If the city lost power for a week because of a substation failure, would you say, “but sometimes you get a flat tire, so now what, huh?!”
- bolo June 26, 2024 (1:05 am)
  
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  When I suffer a flat on my bike I blame the jerks that threw their beer bottles out the window. Or liquor bottles.
  
  About the low (swing) bridge: I’m just happy it’s passable most of the time. MUCH better than the severe inconvenience before it was built. Then you rode up to one end of it, waited for the 15-passenger van with attached flatbed trailer if it wasn’t there already. Lashed your bike on the flatbed trailer and got into the van with a bunch of other sweaty cyclists. Then rode up over the high bridge and down to the other side, unlashed your bike and continued on your route. If you missed the last run you were really SOL. Sometimes the shuttle van was MIA. No bike infrastructure on the 1st Ave. S. bridge either.
  
  The low bridge is really a cyclist’s luxury. No complaints from me. Intelligently designed protected cycle path, smoothly paved. Although maybe it’s starting to show its age.

Kathy June 26, 2024 (9:55 am)

This is why the ST bridge to West Seattle for light rail should have a bike lane, too. We need more options for bike commuting. Portland did it, why can’t we? Water Taxi is great but too infrequent.

Question Authority June 27, 2024 (6:53 pm)

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Why should the taxpayers fund that additional construction cost when the train can, and will carry you and your bike already? That expenditure doesn’t pencil out for the amount of bicyclists served, other routes already exist, just like cars have to take when the bridge malfunctions.

Kersti Muul June 26, 2024 (7:31 pm)

Isn’t the tail lock at the abutment – into the land sides of the spans, not at the center? That’s the center lock

Question Authority June 26, 2024 (9:26 pm)

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The Tail Lock(s) are where the movable swing portions meets the raised ramps on either side. They keep the pivoting halfs stable when the hydraulic cylinder(s) are lowered when the bridge is closed. The locks consist of roughly 1′ square rods which actuate into receiver holes much like a deadbolt in a door. There is a center lock as well, the play you notice while driving over is due to mass, and the clearance required so things don’t bind and seize. It requires a control signal, electricity and hydraulic energy to function, hence when it malfunctions it’s not like changing a flat tire on a bicycle.

Question Authority June 26, 2024 (7:59 pm)

I believe a recall of the SDOT Director is in order, if they can’t keep such a vital, yet complex system in working order for the populace it’s obviously incompetence. Cue sarcasm, the chagrin of others is hilarious when it comes to the lack of understanding they have about the what makes those machines function.