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They did the thing I suggested at 9th and Mercer, and it almost works!

They did it! The Seattle Department of Transportation changed the order of the traffic signals at 9th Ave N and Mercer Street to allow straight traffic, the bike lane and the crosswalk to go before the left turns. This was an idea I first suggested more than six years ago shortly after the new Mercer Street configuration opened. I then made a longer video and post about the idea in April 2022 when I was biking through there every day while doing preschool transportation. Every single time my kid and I tried to get through here heading northbound during the early evening commute, left-turning traffic from southbound 9th Ave would block the bike lane and crosswalk.

I am barely exaggerating when I say “every time.” It was a very uncomfortable and potentially dangerous situation. One of the most common reader complaints I get from folks via social media or email are about this intersection. It is very well-used, providing the most popular connection between the city center and bike routes to most points north. There are no easy solutions to backed-up traffic on Mercer Street since those are caused by traffic getting onto I-5, but surely the city could at least do something to keep the bike and crosswalk open, right?

I am not a signals engineer, but I thought I had a simple fix: Just change the order of the lights. And after more than half a decade, they did it. And the results are…I think pretty good but not perfect!

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I do not have hard data, but I do have footage from before and after since I stood out there for about an hour in 2022 when making my first video. The new signal order does work how I hoped it would, keeping the bike lane and crosswalk clear much more often than before. However, it’s not completely fixed. People on Mercer still often block the box by pulling forward before there is space for their vehicles on the other side. It does not happen as often as before, but it does still happen. I also suspect that the timeframe for blockages is shorter now. I saw almost no blockages until a little after 4 when traffic levels begin to peak. Before, the blocking seemed to begin as soon as traffic was even a little heavy. There were also signal cycles around 4:30 that were fully clear, something that almost never happened before. But keeping people safe and providing an accessible street crossing more of the time still isn’t good enough.

Watching the intersection also highlighted the other inherent safety problems at this intersection as well as many others on Mercer Street. The corner turn radii are so wide that right-turning cars are extra problematic. I saw a lot of near misses, especially between right-turners and people using the crosswalk. People driving can turn quickly into any one of three lanes, and the crosswalk users must travel a surprisingly long distance across all these lanes, leaving them exposed. The city should consider either banning right turns entirely or constructing a physical curb extension or bike lane protection island of some kind so that people turning must make slower and more careful turns. The current design does not work and is not safe. You don’t need to stand out there for very long before you witness a scary interaction. The issue is not that a few people are behaving badly (though some certainly do), it’s a design problem.

Have you noticed an improvement in this intersection recently? Let us know in the comments below.

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10 responses to “They did the thing I suggested at 9th and Mercer, and it almost works!”

  1. Ian Kell

    Tom I bike commute this intersection daily, and the new signal timing works so much better for northbound bikers! thanks!

  2. SeaAnita

    Yay! It’s about time!

    I sent email to my councilman, Dan Strauss, several times about this intersection. Never heard from him….just crickets. Glad your hard work and videos about his finally got someone’s attention!

  3. Al Dimond

    It has been a lot better for northbound biking but… there’s a gulf between, “almost works”, and, “works”, and that gulf is about the distance from the middle of the bike lane to the middle of the crosswalk. That is: in my observation, biking north, when i get the green light the cars are usually just about beyond the bike lane, but still fully blocking the crosswalk, at least at the beginning of the phase.

    As far as fixes for this go, I wouldn’t have a problem with enforcement being one arm of it. I think it would be unfair to ticket left-turning box-blockers at huge intersections like this since they don’t have a good view of whether they’re going to clear the intersection at the point they have to decide whether to enter the intersection. For straight-through traffic I have no such objection, especially for drivers that enter the intersection well into the caution phase. We could give them this incentive.

    On top of this, if we’re really serious about protecting pedestrians, we could use some of the sensor technology we have installed at this intersection to make sure pedestrians have enough time to cross Mercer after the crosswalk is clear by ensuring the walk count-down doesn’t start until a few seconds after the crosswalk is clear. If the sensors installed currently aren’t sufficient to detect whether the crosswalk is clear… then I guess install more sensors or cameras. This may not be a standard feature of the ITS system (I don’t know much about that) but Seattle has been willing to do weird experimental stuff in the past… maybe we could make a feature request to the vendor or hack up some custom stuff. I’m not a huge fan of the general idea of ITS (add more computers to fit more cars down the roads) but if we’re gonna have all this stuff we might as well find applications for basic accessibility…

    1. Al Dimond

      (The long-term solution has always been to just not permit so much office parking in greater-downtown. By “not permit so much” I mean that we should regulate the total amount of parking available in different sub-areas in order to reduce it over time, not simply look at individual projects on an individual basis.)

  4. Peri Hartman

    what do people think about restricting turns from mercer ? i don’t know about right turns, but eliminating left turns would eliminate some of the contention and allow for safer straight-through traffic.

    people who want to make left turns (and possibly some right turns) could use one of the other streets that cross aurora, which wasn’t possible before the tunnel was built.

    eliminating left turns would mean fewer stages in the cycle, meaning less wait time to cross aurora.

    1. Al Dimond

      On the specifics you’d probably have to *sigh* ask a traffic engineer because there is some *sigh* actual expertise in that profession about how many cars there are and where those cars go when you push them around the plate.

      At an armchair level, if we just look at the worst turns from a box-blocking perspective, we’re talking about southbound-to-eastbound lefts (especially during evening rush hour). As I understand it, PM rush-hour Mercer backups reflect a real capacity limitation entering I-5 at Mercer — whatever we do there are going to be queues of cars trying to get to I-5 and we want to manage those queues with minimal disruption to people doing other things (especially people that aren’t in cars… I don’t know if that’s how SDOT thinks about it but I think that’s obviously the right way). Crossing Aurora doesn’t even come into it (if 9th/Mercer is the focus) — it’s just about queues to enter I-5 for traffic that never ventures west of Aurora (a pretty depressing situation IMO). If drivers starting from north of Mercer want to enter I-5 and we prohibit them from turning left they’ll have to continue south across Mercer, then either go around the block in some way to turn right onto Mercer, or use some other I-5 entrance.

      Both of these would increase traffic south of Mercer, especially east of 9th Ave N (the Cascade neighborhood). Whether this would be a big problem sorta depends on how many cars we’re really talking about (i.e. real numbers, the actual expertise of traffic engineers). I suspect some of the intersections, especially along Republican, would need more intensive controls to deal with the increased traffic safely. This could also push more drivers to Denny and make the 8 even worse. For those people that want to re-route the 8 off Denny and fully commit Denny to its role as a sacrifice to Seattle’s embarrassing failure to plan SLU development reasonably… the impacts on other streets would also probably make this alternate version of the 8 even worse.

      My inclination is to believe that the left turns are the least-worst option — that it’s better to keep as much of that as possible from leaking south of Mercer. But if the real numbers say that it’s really a tiny number of cars turning left and they just have an outrageous impact at streets like 9th (and a couple others nearby), maybe forcing them to cross and go around the block would be better. Anyway my real inclination is to say that when you have problems like this, the only way to win is not to play — to limit office parking, and to use enforcement (where it would be fair and effective) to create incentives against outrageously selfish driving, etc. Don’t make everyone a traffic engineer to talk about the future we want, build a future where traffic engineering doesn’t matter as much…

  5. Peri Hartman

    very well explained, al. one note, i was talking about limiting left turns *from* mercer. but i think your expectations would be more out less the same.

    none the less, reducing the cycle time would make crossing mercer easier. and anyone bicycling in that area probably has to cross mercer.

  6. NoSpin

    There actually IS an “easy solution” to backed-up traffic on Mercer Street: good old-fashioned traffic cops in the middle of the intersection directing traffic, with a few back-up officers to pull offenders aside.

    It’s a low-tech solution that could be implemented tomorrow, and would probably pay for itself while greatly enhancing safety of pedestrians and cyclists.

    The only thing standing in the way is SPDs willingness to do a little useful work.

  7. Jaws

    Move to Arizona… all their signals are left AFTER straight.


    I appreciate the callout, and have noticed the difference on my daily commute… the afternoon bike lane is blocked for me less than half the time versus daily prior to the signal change. On “Seattle Cars in Bike Lane” this was the most reported intersection in the last year, and volume seems to have decreased… I no longer report on the daily.

    This intersection was just featured in a King 5 Seattle feature called “Send Shante” to help call attention to this issue. It mentions there was consideration for camera enforcement of blocking the box, but unfortunately wasn’t feasible for the initial rounds of installation.

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