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Watch: A $0 fix for the notorious 9th and Mercer intersection

Every day during busy travel times, people turning left from southbound 9th Avenue N block the bike lane and crosswalk across Mercer Street. This happens every signal cycle, forcing people to try to find a path through the mess of cars and trucks just to get across the street. It has been this way for years.

After witnessing this blockage every day on the way home from my kid’s preschool, I became convince that there is a $0 fix to the problem. Well, “fix” is maybe the wrong word. But for $0, the city could make the bike lane and crosswalk much more usable. It is such an obvious solution that I’m sure I am not the first person to think of it (though I did suggest it a half decade ago when it opened). I made the video above to explain the concept.

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Mercer Street’s traffic signals have a so-called “Intelligent Transportation Systems Program,” which is supposed to dynamically adjust the signal timings based on the needs of street users. But it is not very “intelligent” if it allows this complete failure to occur every single day for years on end. The problem is that the ITS Program is designed to prioritize vehicle movement, not to make it easier to walk or bike. This is the same system that steals crosswalk time and gives it to cars.

It’s time for some old-fashioned human intervention.

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13 responses to “Watch: A $0 fix for the notorious 9th and Mercer intersection”

  1. Gary Yngve

    great idea! only disadvantage of left turns after is that if the left turn lanes are not long enough, the jam will propagate north, affecting southbound traffic. SDOT should have simple simulation tools to experiment with your idea.

  2. Amy

    hell yeah Tom. This rules. I just sent a note to Seattle DOT and the City Council Transportation Committee linking to it and expressing my support for the idea.

  3. Chris

    Block the box cameras that result in tickets for cars that enter the intersection without room to exit it. Simple and better for cars bikes scooters wheelchairs and pedestrians

    1. Tom Fucoloro

      Later in the video I talk about how people turning left don’t really have a choice. If they don’t go when they get the green, then they’ll never get a chance to go. It’s always backed up. Mercer is broken, and in this case I don’t think camera tickets will fix it. Camera tickets are good when only a small number of bad actors cause the problem. In this case, the street is so broken that nearly everyone turning left would get a ticket.

  4. Dave

    This seems like a really promising $0 fix. The only disadvantage would be if the left turners from 9th block the box at the end, and then the eastbound Mercer thru traffic goes, and they end up blocking the box too, then the box will still be blocked when the northbound 9th traffic and peds/bikes wants to go. But if I recall, the Mercer thru signal itself is super long, so there is likely to be plenty of time for the box to clear during that cycle. And the straight thru traffic on Mercer seems better at not blocking the box in general. If I believed changes could happen easily in Seattle, I’d say this would be an easy no brainer of a change.

    1. NoahM

      Yeah, the eastbound Mercer traffic was my first concern with this proposal. I think they will end up blocking the bike lane and crosswalk, rather than the people making left turns on to Mercer in this scenario. Traffic on Mercer west of the light would end up backed up, with impact to other intersections that I can’t predict right now (Dexter?) But I think at the very least it’s worth running a real-world experiment with this idea. Apply Tom’s proposal for a week or a month or whatever and let’s see how it goes.

  5. Cam Solomon

    Part of the problem is guidance.

    Right now, SDOT is inexplicably suggesting everyone go to Denny, the worst car sewer in the city, to get to I-5.


    Nobody who knows the city even a little bit is foolish enough to do that.

    Since I lived in Fremont for years, I know the best way is to do the early turn and get off 9th. That turn onto Westlake is often not as bad.

    I’m not sure if it causes the same problems with blocked crosswalks. Probably.

    But perhaps if SDOT wasn’t being so disingenuous, and sending people into a half-hour of gridlock on Denny, people might consider taking guidance to take Westlake instead.

    Also. Your idea. ;)

    1. Cam Solomon

      Looks like I misinterpreted when they meant with that Denny sign. I’m probably not alone.


      Maybe have some sort of trade off, choosing either Westlake or 9th, and the car route. Probably Westlake makes more sense, with the bike route on 9th.

  6. RachaelL

    I believe SDOT prefers the signal order this way because they are institutionally focused on vehicle throughput. Having the left phase as early as possible provides a small but significant amount of extra space and time for vehicles to queue which in their modeling probably prevents severe backups spilling back to Westlake.

    So yes this is an “easy” fix but as with somehow a brand new rebuilt street being unable to have block the box cameras mounted, it will be deemed “impossible”.

  7. Part of the problem is allowing left turns at all. With aurora below grade and three new crossings, why does Mercer need so many left turns ? People can learn to take one of the other streets if they need to make a left. Without the left turns, there would be more cycle time for other users, like peds & bikes. And, perhaps, the traffic jams would go away.

    In more detail: if westbound on mercer, the left turn at fairview should be retained. From there, one can easily get to any place in SLU or to 99 southbound. If eastbound on mercer, turn right on 5th N and then left on one of the other streets that cross aurora. From there, again, one can easily get to any place in SLU. I will admit, it’s slightly less convenient if trying to access dexter or westlake northbound. Although, maybe not, if the traffic backups diminish.

  8. JB

    Omg this spot drives me crazy. I have started experimenting with crossing Mercer northbound on Terry or Boren, but haven’t gone those routes enough times yet to decide if they are really viable alternatives. Looking at your diagram of the intersection, I’m also wondering if maybe it would work to cross to the west side of 9th and bike northbound on the sidewalk for a block or two.

    By the way, the real fundamental solution for this problem (and so many others) is congestion tolling; but not holding my breath for anyone around here to find the political will for that in the foreseeable future.

  9. Merlin

    Such a smart and simple idea. I bet they used the old map without the crosswalk and bike lane when they programmed the signal. But the only real solution is ban cars.

  10. What if only northbound traffic went first, both straight and left turning? And then southbound traffic can do whatever southbound traffic needs to do (mostly getting tangled in the Mercer Mess).

    I’d be interested to know if SDOT did do scenarios for all iterations and chose the one that exists now because it “prioritizes” people going traveling to the I-5; damn the rest of us (people heading north, etc.).

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