Adaptive Signal System Kicks Pedestrians To The Curb

Carolyn Mawbey is irked. The feisty 68-year-old former New Yorker gets around Seattle’s Uptown neighborhood mostly on foot but when the transportation department flipped a switch this spring, her Earth-friendly commute got considerably rougher. “At first, I thought there was something wrong with me. I used to get across the street in time and then the walk signals started switching to don’t walk before I could get across.”

It turns out the problem wasn’t the spring in Ms. Mawbey’s step. Quietly, right around April Fool’s Day, the Seattle Department of Transportation (SDOT) activated a new adaptive traffic signal system along the Mercer corridor. The system, according to SDOT, is intended to be a smarter approach to moving traffic.

While SDOT activated the system without fanfare, people who live and work along Mercer started noticing changes right away. Walk signals—previously switching from one phase to the next in a familiar rhythm—seemed to go haywire. Sometimes the walk phase would cut short, prompting people like Ms. Mawbey to sprint to the opposite curb (or suffer the wrath of turning cars). Sometimes the walk signal would appear, then time out, then suddenly turn to walk again, all while parallel vehicular traffic had a solid green.  In the worst cases, the walk phase would be eliminated entirely for two or more cycles.

In the midst of this confusion, many pedestrians engaged in risky behavior, walking against the light and wading into traffic, or giving up and finding a different route. If Mercer were a suburban commercial strip, perhaps these changes would be considered just the latest indignity. However, the Mercer corridor cuts through the northern part of Seattle’s urban core, home to the Space Needle, Amazon, the Bill and Melinda Gates Foundation, and many of Seattle’s most prized commercial, cultural, and research institutions. The street life of this regional engine of creative activity and economic growth was being sacrificed in the name of getting cars to the interstate faster.

Adapting, but to whom?

It’s called an adaptive system because signal timing adapts to demand from users. Demand from cars is measured directly using inductive loops installed in the pavement. Demand from pedestrians, however, is less accurate. It depends on a person pushing a beg button, which some people do and some people don’t.

After observing risky behavior for more than a week, advocates recorded people trying to cross at the corner of 1st Ave N and Mercer. In the video below, at :08, a blind gentleman tries and luckily succeeds in navigating the crossing against the light.

The adaptive signal system had been in the works for several years. Sensors and other instruments were installed during the years-long Mercer Corridor Project but all those components, along with computer hardware and software, need to come together in a command center. So, SDOT built their system, officially dubbed SCOOT (for Split Cycle Offset Optimization Technique), in a piecemeal fashion as funding became available.

A peek inside SDOT’s traffic control center where the adaptive system is monitored. (Mark Ostrow)

After millions of dollars, years of implementation, and several weeks of post-deployment observation, SDOT Director Scott Kubly held a press conference at the 37th floor of the Seattle Municipal Tower to unveil the system. Press coverage was uniformly glowing. The Seattle Times gushed “New, high-tech traffic signals make the Mercer Street trek less messy.”

Was the juice worth the squeeze?

The reality was not quite as rosy. The gains for cars were modest and the cost to safety and pedestrian mobility was high. Average travel time for cars moving in the westbound direction from one end of the corridor to the other, according to SDOT’s own figures, actually got worse. Eastbound travel times showed improvements of 18 seconds in the morning and 2.7 minutes in the evening. Meanwhile, people on foot were experiencing waits of more than three minutes just to cross the street. These small gains for cars were likely at the expense of people walking.

It’s worth noting that SDOT’s before-and-after evaluation didn’t include measures of pedestrian impacts. Were the needs of people walking even considered?

Torches and pitchforks

By this time, neighbors were getting increasingly vocal. KIRO TV ran a feature story on April 27th highlighting the failings of the system but SDOT didn’t seem to be listening (except for City Traffic Engineer Dongho Chang, who took an interest and facilitated dialogue between concerned citizens and the SDOT signals team).

Pedestrians don’t like the signal timing on Mercer @seattledot.

Improving walking and biking connections between Uptown and South Lake Union is a major priority for Seattle Neighborhood Greenways. So, on May 30th, Queen Anne Greenways, together with the Uptown Alliance and South Lake Union Greenways, organized a walking tour to highlight the problems on Mercer. Thirty-five participants—including SDOT representatives, members of the press, neighbors, and advocates—braved intermittent drizzle with a different volunteer leading discussion at each stop.

Map of the Mercer Walking Tour route. (Mark Ostrow and Google Maps)

Right away, it was abundantly clear the new signals weren’t working for people on foot.  When the group attempted to cross Mercer at 1st Ave N, the signal skipped several cycles and the large crowd waited for several minutes just to cross. This pattern was repeated at various stops along the way and it became clear that something needed to be done.

Uptown resident Carolyn Mawbey (foreground left) patiently waits to cross Mercer alongside SDOT City Traffic Engineer Dongho Chang (foreground right), while other tour participants pass the time. (Mark Ostrow)


SDOT deserves credit for sending a high level delegation including Director Scott Kubly, Deputy Director Benjamin de la Peña, City Traffic Engineer and local legend Dongho Chang and Traffic Operations Manager John Marek. They listened, observed, and engaged in a lively exchange of ideas.

In the end, SDOT expressed a willingness to address the following items:

  1. Extend crossing time for pedestrians while parallel cars have a green light.
  1. Prevent signals from skipping the walk phase during any given cycle.
  1. Provide a protected left turn signal for west-to-south traffic at Queen Anne Ave & Mercer.
  1. Address the missing button at Roy St & 3rd Ave N.
  1. Re-evaluate average vehicular travel time to assess whether induced demand has erased previously measured improvements.
  2. Include pedestrian delay or other pedestrian service metrics in future evaluations.

Additional asks that didn’t get clear agreement from SDOT included the following actions to prioritize people walking and biking in Uptown and South Lake Union:

  1. Provide a walk signal without requiring actuation, particularly at Queen Anne Ave & Roy St and at Terry & Mercer, two crossings specifically designed to prioritize pedestrian mobility.
  1. Prioritize transit crossing Mercer in a north-south direction, particularly at Dexter Ave.
  1. Measure compliance with pedestrian actuation requirements and consider such data when requiring actuation.
  1. Include cyclist delay or other bicycle service metrics in future evaluations, particularly on routes crossing Mercer.
  1. Seek to more accurately incorporate pedestrian (not just vehicular) demand into their algorithms and ensure the system responds to it.
  1. Prioritize non-motorized modes.
  2. Address the issues with adaptive signals in the Mercer corridor before expanding use of the system.

What’s next?

Mercer represents the first SCOOT implementation in Seattle but it won’t be the last. Soon, SDOT hopes to roll out the system along Denny Way, a parallel corridor that cuts deeper into Seattle’s urban core, and more streets after that.

Meanwhile, Seattle’s mode-split goals may hang in the balance. Uptown resident Carolyn Mawbey might not be coaxed back into her car but others might. Will the system simply induce additional vehicular demand, erasing the modest gains in travel time observed in the first few weeks, while locking in the losses for pedestrians? Will Seattle drop more car-centric suburban traffic signal systems into the center city or will it direct scarce resources towards preparing for a denser future where walking, biking and transit access are prioritized? That remains to be seen.

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Mark Ostrow serves on the Board of Seattle Neighborhood Greenways and is a core leader of Queen Anne Greenways. Mark is a principal at RK2 Advisory and a Trustee at Northwest Kidney Centers.

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It’s so gross that SDOT is still implementing “cars first, run over the pedestrians” policies. The 1950s ended 60 years ago, guys.

Harriett & Harvey

We are 50-year Seattle Center regulars (coming from Central Seattle to opera, ballet, theater & other Center events frequently, parking on the street north of Mercer and walking to the Center. Even before this “adaptive system” went into effect, the pedestrian walk lights across Mercer all along the Lower Queen Anne corridor (from 5th Avenue North to 1st Ave. N.) were ALL far too short, even for fit, fast walkers like us (who are still backpacking at 71). The red lights would start flashing when we were only in the middle of the wide crossing corridor. We immediately assumed that, once again, all of the improvements of the Mercer corridor made by SDOT have been designed solely to benefit all of the big businesses concentrated in South Lake Union (Vulcan, Amazon, Gates Foundation), including heavy commuting vehicular traffic — City planning once again trumped by the big Money-Talks businesses to the east of the People’s Seattle Center.

Hats off to Neighborhood Greenways advocating for increased safety for pedestrians of all ages and abilities, cyclists, and all other non-motorized forms of transportation — shouldn’t all of us be at the top of the list for SDOT improvements to our streets? And whatever happened to SDOT priority on increasing pedestrian and cyclists safety record adopted last year? (And what’s the matter with synchronized traffic lights E/W on Mercer to optimize traffic without spending millions on a new “adaptive” system which appears to be a net failure to date — like, it’s hard to synchronize the lights? We’ve wondered for decades why the Mercer lights have never been synchronized for smoother flow of E/W traffic as the most obvious and least expensive alternative to ‘fixing’ the Mercer Mess.) Is newer always better? Harriett Cody & Harvey Sadis

Mike Carr

The goal was to optimize East/West traffic on Mercer. Pedestrian walk times/delays were either unintentional consequences or intentional sacrifices to meet the original goal.


I live in Pittsburgh, PA – although as luck would have it, I stayed at the Maxwell for 10 days last year so I’m somewhat familiar with the area you’re describing.

We have a system here: that has been in operation for 5 years, and the parallels are astounding -starting with justifying its existence by touting “travel time reduction” with no consideration of the impact on anything other than motor vehicles. The green signal in the “primary” direction was considerably lengthened (even at non-peak times, ~2 minutes is not uncommon) while the pedestrian “walk” intervals were shortened to the bare minimum. If the beg button is not pressed prior to the cycle, there is no “walk” signal at all. I’ve also experienced a pedestrian signal directly adjacent to my office that never turned to “walk” at all: – which they “fixed” by adding more beg buttons of course. This is all compounded by some truly horrific intersection designs, most notably this one:

I have been outspoken about these issues for years now, but haven’t been successful in getting the city to reconsider – instead, they keep expanding the system, and I see the same effects everywhere. However, I do find some encouragement from what you’ve accomplished in Seattle, and hope that you are successful in getting your concerns addressed.


Time for some hacking? Open up those signal boxes and reprogram them to provide permanent reds for the cars, perhaps. This is ridiculous.


There’s a similar situation at Aurora and 95th, where the north/south walk signal will count down and then start all over again, even when traffic is very light (but not light enough to jaywalk, given the width of the road and the average speed of the vehicles). Obviously the street life in that area isn’t anywhere near as on Mercer, but it can be frustrating.

You’d think that people would test the signals for *all* modes of transportation before locking in any settings (how hard are these things to recalibrate, anyway…?) but I guess that’s what happens when you forget about the human element.

Carolyn Mawbey

I’ve been carefully watching how walkers interact with the newly shortened pedestrian cross signals along West Mercer Street between 3rd Avenue West & 1st Avenue North in Uptown. There are significantly more jaywalkers now that the adaptive traffic signals have been enacted here. Furthermore, many cars seem almost emboldened by having longer lights, & rapidly try to make left or right turns with little heed to any walker who may be in the crosswalk, even when a walker has the “cross” signal. But what really concerns me is so many pedestrians look confused when they try to cross the street & discover that they do not get a cross signal in any direction. After standing on the curb looking confused about why they can’t get across the street, most of them ultimately wind up jaywalking out of frustration. The more I pay attention, the more I realize how the new adaptive pedestrian cross signals have made it significantly more dangerous for walkers in Uptown. In an urbanized environment in a city as developed as Seattle has become, pedestrian traffic should be considered to be a major way that people get from place to place. Like driving or the bus, walking is a form of transportation in an urban environment. Unfortunately, in programming the adaptive traffic signals this way, Seattle seems to have taken a step backwards, & has created a situation far more dangerous for the pedestrians who live & work in this neighborhood. I wouldn’t be at all surprised if this results in more pedestrians being hit or killed by motorists now.


Yeah, the timing for everyone, except those on driving east-west on Roy or Mercer, has gotten worse. Thanks for the write-up. I’m expecting the SDOT changes/fixes to fall short of where they need really be.
Here are just two examples of how bad things are in the corridor, based on what I’ve seen.
-The eastbound pedestrian walk time at 3rd Ave W & Mercer is SHORTER than the eastbound bus queue jump green light. That means by the time cars get the green, the pedestrian countdown is already going. And the car green stays on for 20-40 more seconds after the countdown is done.
-The southbound queues from 9th/Westlake & Mercer can back up to Highland Dr on Westlake in the afternoon for those on the route 40… far beyond the extents of the bus lane.

Mike Carr

There is also a light rail train on tracks in SLU. Watch out for that.

Betta Orshansky

I live in Uptown and I agree, the timing of the lights are a nightmare. I have a dog and a baby in a stroller and we have to HUSTLE to get across Mercer. It was bad before, but the timing of the lights now has made it worse.

Walking around South Lake Union is a very unpleasant experience. The intersection at Mercer & 9th Ave. N. is a complete disaster with pedestrians, bikes, and cars going all over the place. It honestly reminds me of being in China where the intersections were basically a free for all.

But won’t stop walking!

Glen Buhlmann

Here is Mercer @ Terry on my way to the SDOT walk. It’s insane at this intersection, Every. Single. Day.

Many more people cross against the lights than with the lights. This is incredibly dangerous and will eventually result in injuries and deaths. But when the system treats people walking this horribly, SDOT knows that people will not respect the system and will ignore it.

So SDOT knows that their design of Mercer is going to put people at risk. Let’s see what they change. I’m not holding my breath.


This terrible pedestrian light programming has nothing to do with adaptive signals. It’s just plain stupid programming, which can exist with adaptive or traditional signals.

There’s absolutely no reason why pedestrians should get a don’t-walk during Mercer’s green. Terry is one way into the intersection, so there’s no turning conflict. And there’s no need to start the ped countdown early to allow a variable-length green to end without advance notice, since Terry is very narrow so the flashing hand won’t be much longer than the yellow light anyway.

In this case it isn’t really a safety issue. It’s just disrespectful, and breeds contempt for the law.

Glen Buhlmann

Thanks for saying that. Totally what I think but prefer SDOT folks see some of this as not just coming from the couple daily ranting folks that they probably tune out at some level even if everything that Mark and I point out daily are completely valid criticisms.

Glen Buhlmann

Not to mention that when traffic is not moving at all in either direction on Mercer, or even just not moving in the direction that 80% of the motorists are trying to go, it makes no sense to keep that light green while even 1 person on foot, never mind 1 bus, is waiting to cross Mercer. Adaptive signals can do this. SDOT just doesn’t see this as a goal.