WSDOT is testing out a less bumpy gap cover on the 520 Bridge trail

Base photos from WSDOT.

The trail on the 520 Bridge is amazing, except for one annoying and possibly dangerous detail: The metal plates that cover the floating bridge’s expansion gaps are jarringly bumpy. It’s a frustrating detail in what is otherwise a wonderful experience (well, as wonderful as being next to a freeway can be).

Well, great news! WSDOT installed a demonstration gap cover yesterday to test a design that is hopefully less jarring and meets all their engineering criteria (the plates need to handle heavy loads in case the trail is used for maintenance vehicles). It is located near the east end of the bridge, and WSDOT is hoping to gather feedback from folks about whether it addresses the issue. Text (206) 200-9484 to submit feedback.

  • This is an improvement, upgrade all similar plates: text “A
  • I didn’t notice a difference/the old plates are fine: text “B

You can also post to social media using the hashtag #RateThePlate.

We noted these bumps before the bridge opened and argued that the state should smooth them out so they are not so jarring. When biking, you hit a bump every few seconds. This is annoying, for sure, and diminished the otherwise pleasant experience of biking across Lake Washington. But my main concern is that someone will not be expecting such a bump on a brand new trail and will crash.

I have not yet heard any reports of crashes caused by these gap covers, which is a good thing. But it is still worth fixing the issue to be sure.

From the photos, it certainly appears to be a much less jarring bump, though Seattle Bike Blog has not yet had a chance to try it out. Have you biked across the 520 Bridge since the new plate was installed? Let us know your thoughts in the comments below.

More details from WSDOT:

State Route 520’s new trail across Lake Washington has garnered high praise from more than 300,000 users since its December 2017 opening. Bike riders, runners, dog walkers and folks out for a relaxing stroll tell us they’re delighted to have a new, foot-powered trail with scenic lake and mountain views. And many pedal-pushing commuters say the new trail, as an alternative to I-90’s cross-lake connection, is cutting significant time off their daily treks between the Eastside and Seattle.

There’s one aspect of the path that’s not getting rave reviews: the narrow steel plates covering the trail’s expansion joints on the bridge. Some bike riders tell us the plates are jolting, especially for road bikes with skinny, highly inflated tires. I’ve ridden the trail myself, several times, and experienced the thump of each joint cover.

I’m glad to report that we’re working on a remedy. Our engineers developed and installed a prototype plate designed to ease the bumps cyclists experience while crossing the floating bridge. The new cover plate design won’t completely eliminate the bumps – but it should produce a marked improvement.

That’s where you come in. Now that the prototype cover plate is installed, we’re asking riders to #RateThePlate. After biking over the replacement plate (located near the east end of the bridge) we’re asking riders to text us at (206) 200-9484 to rate their experience with two options:

  • This is an improvement, upgrade all similar plates: text “A”
  • I didn’t notice a difference/the old plates are fine: text “B”

We’ll solicit feedback through the end of the year. If we hear that the plate provides a better ride, we’ll manufacture and install replacements for all 27 existing narrow cover plates.

Why the path has cover plates
The roadway on the new, 1.5-mile-long floating bridge has expansion joints on each end of the 23 massive, concrete pontoons supporting the structure. The joints allow the bridge to expand (or contract) horizontally as air and water temperatures change. They also allow the bridge to flex vertically as the lake’s water level rises or falls. On the shared-use trail, there’s an open gap at each joint that varies in width from about 2 to 4 inches. Left exposed, a gap of that size could be hazardous to someone with a cane, a skateboarder, or other trail users. So we added cover plates over each joint to address the safety risk that open gaps would pose.

The trail’s existing steel cover plates are a half-inch thick, with a flat top, beveled edges and a rough, nonskid surface. When designing the bridge, we used federal guidelines to ensure the plates’ compliance with the Americans with Disabilities Act.

The plates also play a role in the integrity of the bridge itself. The roadway and shared-use path are elevated 20 feet or more above the lake’s surface. This design feature keeps vehicles, bike riders and pedestrians wave-free during windstorms. It also gives our crews ample room for inspection and maintenance of the pontoons below.

Because the bridge deck is elevated – up to 70 feet on the east high-rise near Medina – we use a special truck, equipped with an extendable, hinged arm and crew basket, for inspecting the underside of the bridge. This 3-ton vehicle travels along the trail for these inspections, so the cover plates must be strong enough to support its weight. Moreover, emergency vehicles, including fire trucks, might have to use the trail if a major incident blocked the roadway.

A tale of two trails
A few bicyclists have asked us why the older, narrower shared-use trail on the I-90 floating bridge is smoother than the new SR 520 Trail – without the expansion-joint bumps. The answer, once again, relates to SR 520’s elevated roadway.

In the same way traffic moved on the old SR 520 floating bridge, all I-90 traffic crossing Lake Washington – including bicycles – travels directly on the pontoons’ concrete surface. That means there are no heavy trucks making under-bridge inspections from I-90’s shared-use path – and no need for sturdy cover plates on that path’s expansion joints.

The new SR 520 Trail is a wonderful addition to the region’s expanding network of trails, and we want your experience of riding the trail to be fabulous as well. Be sure to #RateThePlate after your next ride!

Photo from WSDOT

About Tom Fucoloro

Founder and Editor of Seattle Bike Blog.
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19 Responses to WSDOT is testing out a less bumpy gap cover on the 520 Bridge trail

  1. Brad Niemeyer says:

    That’s great news that a fix is in the works. I will rate the plate. It is a glaring problem with the otherwise wonderful 520 bridge trail.

  2. Andrew Sapuntzakis says:

    “ADA compliant” probably means it’s not going to cause problems for a 3- or 4-wheel vehicle below 8 mph. That’s bound to be different for a 2-wheel vehicle at 10-20 mph.

    So is the plate marked, or are people supposed to guess which is the “smoothest”? Is it the the eastern-most plate?

    Not to be cynical, but “existing plates are fine” and “didn’t notice a difference” are not the same thing – shouldn’t there be an option for “still too jarring”?

    The comment period seems short, during a time of low usage.

    • SR 520 Team says:

      Hi Andrew, thanks for your comments. The plate was marked with a flag but it was removed so we re-marked the adjacent railing with green ribbons. Plus someone spray painted “test” on the plate – so it should be easier to locate – it’s the second-most eastern narrow plate. Thanks for the feedback about the survey question – it was meant to capture the sentiment of “this plate isn’t a solution” – whether that’s because it didn’t make enough of a difference, or because you thought the old plate was fine (which, yes, we have heard that feedback). As for the comment period, we’ll reevaluate at the end of the year and see if we need to extend it. That being said, we’ve already gotten more than 240 responses with 95% of the respondents favoring the new plate. – SR 520 Project team

      • Andrew Sapuntzakis says:

        Thanks for working to fix this.

        I rode the 520 this Saturday, and I agree with Buscommuter’s observation – the marked joint seems to be on the low end of the range. Don’t recall how jarring that joint was before, but it would be great if that was the new worst-case.

        Is there a viable (ADA-compliant) “no-cover” or “same as the cars” option?

  3. asdf2 says:

    A few months ago, I made a special point to buy a bike with wide tires and a front suspension specifically because of those plates. With that bike, I can plow over them at 20mph and be fine. On my other bikes – or Lime bikes, for that matter, I find myself slowing down to about 5 mph for each plate cover.

    Good to know they’re working on it.

  4. PETER KRYSTAD says:

    I crossed the bridge Wednesday a few hours after it was installed. It’s better, but you can still feel a bump.

  5. Southeasterner says:

    Off topic but ugh ugh ugh on the Missing Link news.

    Amazing that a few business owners, with extremely weak arguments, are able to derail the construction of an inevitable project and add millions to the cost for all Seattle tax payers.

    What added insurance will they need? No other business along the rest of the Burke or Ship Canal bike trails are paying increased insurance because they are adjacent to route that is safe for non-motorized traffic.

    Once city clears this pointless hurdle with another $1 million of costs I’m sure the Ballard “Coalition” will go to item number 2 on their list of objection points and we can continue on this game for another 20+ years.

  6. asdf2 says:

    So, assuming we’re willing to take whatever parking is necessary to get a protected bike lane on Leary and Market, is what the appalants are asking for that bad?

    Or, is the concern that we would never really be able to take away half the parking on Leary without causing other businesses to sue and delay?

  7. Buscommuter says:

    The plate is better, but not much.
    Basically there is quite a Range in the joltyness between the existing joints. Especially on the eastern descent. This new plate is at the lower end of that range.
    So yeah, if they could all be like that it’d be an improvement.

  8. Seattle Bellevue Commuter says:

    Exactly where is the new joint? I’ve crossed it several times since it was replaced and haven’t been able to tell which one is new. It would be nice if they flagged it. I guess my response will have to be B, no difference.

  9. kDavid says:

    My observation is the same as Seattle Bellevue Commuter – I went out today _specifically_ to find the new plate and see if there was an improvement. But alas, I could not find it! Here’s my garmin track ( ) – I even went back and forth full length 2x, plus one more slow pass loop on the east end!
    So I guess I should text B? Except that implies that it’s better? But really what I want to say is that it is not an improvement and they need to go back to the drawing board? Why not engage the UW Engineering department for a fix? C’mon WSDOT, it’s a pain in the joint for cyclists, scooterists, wheelchair users, skateboarders, runners & joggers (well, it could be for a tired jogger, right?). This is a multi use trail that is suffering for a motor vehicle based reason – that doesn’t make sense. And guess what – the gap does not have to support your heavy service vehicle across it’s whole width – why not make the center bit real smooth for the non motor vehicle users?? (ie: recessed plate?).

    • Seattle Bellevue Commuter says:

      I’m not sure they are focused on the right area. The issue is not necessarily the amount of rise at the joint. It’s the rapidity of the rise, within a few inches on either side of the joint, which works out to a fraction of a second for the bike to absorb the build up.. I don’t understand why they don’t slowly taper the concrete or otherwise gradually build up to the joint.

      • SR 520 Team says:

        Hi, thank you both for your comments. The plate is the second-most-eastern narrow plate, and we’ve now marked it with signs and a ribbon. If you don’t find the plate to be an improvement, please text “B” – that lets us know that, whether you think it’s still too much of a bump, or you didn’t think it was a bump in the first place, the new plate isn’t enough of an improvement to replace all the other narrow plates. We appreciate your feedback – and for the record the new plate does have a shallower rise (1:6 ratio) compared to the original plate (1:2 ratio). Essentially, the new plate lines up with the curve of a bike tire, the old plates (existing) did not. – SR 520 Project team

  10. AW says:

    Can anyone point out exactly where the new joint is located ? Perhaps I am being cynical but perhaps WSDOT is hoping that the outcome will be that no one noticed the difference and not bother actually fixing the problem. There are so many problems with their approach:

    * They are asking does this new expansion joint suck less than the old one rather than how do I fix the problem.

    * It is winter and at least I am using my heavy fat-tire bike and so do notice the bumps less than in the summer on my skinny 23c tires.

    * Right now it is dark during my commute at least so it would be difficult to find the new plate.

    * A few should be replaced on the west end towards the bottom of the hill there – this is where people will feel it the most given that is where bikes will have the most speed.

    I suppose it is good that there is an effort to fix this but they have known about this for a year.

    • SR 520 Team says:

      Hi AW, the new cover plate is the second-most-eastern narrow cover plate, near the east end of the bridge. We originally marked it with both a sign and a flag. We’ve since heard the flag was removed, so we’ve added another sign and ribbon to mark the plate (pictures here: Good news – lots of people have noticed and we’ve received more than 240 responses, the vast majority (95%) of which find the new plate to be an improvement. Since the trail opened we’ve heard from a number of cyclists with various ideas on how to improve the plate. In response to that feedback, our engineers designed a plate to both meet engineering requirements and reduce the bump cyclists experience. We’ll keep gathering feedback through the end of the year and determine our next steps based on what we hear. – SR 520 Project Team

  11. Peter says:

    The new joint cover is at the very eastern end of the bridge, a little west of the pullout/”lighthouse”. I stopped and had a closer look this morning than my pass in the dark and rain last week. To me it is a clear improvement, much thinner. I really appreciate WSDOT responding to the issue, frankly I find it a little surprising they are making the effort. But not surprisingly it appears to be the same design as the covers used on the 520 36th NE overpass in Overlake that is also part of my bike commute and was built, what, 15 years ago?

  12. GARY S ANDERSON says:

    Pretty hard to find. Probably anything is an improvement.

Comments are closed.