South Lake Union Is For Cars


Seattle, we need to talk. It’s undeniable that we are creating the model for an urban high-tech corridor that eschews the inefficient sprawl that has been so entrenched in the American tech sector for the past few decades. Out with the sprawling corporate campus, in with the vertical one. Instead of creating your own suburban style streets, utilize the existing street grid and harness the power of an urban center city. It’s pretty clear how beneficial this new path will be for the planet, and for the economic health of cities themselves.

South Lake Union (SLU) and Denny Triangle are this model. And if Seattle as a whole is going to rebel against increased density in order to relieve the intense pressure that economic growth is putting on housing prices, we can all agree that making the SLU urban center more dense with both housing and office space is one of the most practical solutions we have.

Unfortunately, we forgot to do one thing on the way to making this a reality: leave out the cars.

Take a scroll through the dozens of building projects currently going through the design review and permitting process in South Lake Union and Denny Triangle. The number of parking spaces planned for an area with a street grid that’s already packed with cars during peak periods is astounding. Several planned developments include over 1,000 parking spaces each, including 1120 Denny Way project and the 300 Boren Ave N project. Amazon’s three-tower complex down Westlake at Virginia Street, in addition to being home to the photogenic biospheres that open next year, will also be home to more than 3,000 parking spaces in total.

After spending $140 million on upgrading the Mercer Street corridor to “clean up” the I-5 congestion, the Seattle Department of Transportation (SDOT) has only ended up proving the efficacy of induced demand and the futility against trying to build our way out of a car-heavy present. Now the department seems intent on placing a big cherry on top in the form of a million dollar traffic signal timing improvements that simply seem to reprioritize car travel during peak hours to I-5 eastbound.

Motorized traffic changes on Mercer Street eastbound from signal modifications. (City of Seattle)
Motorized traffic changes on Mercer Street eastbound from signal modifications. (City of Seattle)
Motorized traffic changes on Mercer Street westbound from signal modifications. (City of Seattle)
Motorized traffic changes on Mercer Street westbound from signal modifications. (City of Seattle)

Transit riders and pedestrians in the corridor have immediately noticed the impact that the new timing is having on their travel around Mercer. Because there isn’t any east-west public transit on Mercer in SLU, prioritizing east-west travel means deprioritizing transit. How exactly SDOT is planning on running a RapidRide route up Eastlake through Fairview while still prioritizing traffic onto I-5 is only one of the upcoming challenges, to say nothing of the transit riders currently wondering why their bus is sitting at Mercer behind cars blocking the lane.

As for pedestrians, the new signals are frequently cutting pedestrian crossing time short while still allowing traffic to move in the same direction. When traffic is stop-and-go, and no vehicles are moving through the intersection anyway, this encourages pedestrians crossing against the crossing signal. Creating an environment where the pedestrians must judge for themselves if they are going to wait for no perceived reason or just go for it sounds familiar–it’s exactly what happens near our at-grade light rail stations on Martin Luther King Jr Way S where pedestrians can sometimes wait 10 minutes for a walk signal that grants permission to walk a few feet.

Dubious carbon savings assumptions for the Mercer ITS project. (City of Seattle)
Dubious carbon savings assumptions for the Mercer ITS project. (City of Seattle)

The documentation around the Mercer ITS (Intelligent Transportation System) is really quite remarkable as it shows just how deeply entrenched the commitment to Level of Service standards are at SDOT, despite all of the seeming progress toward complete streets, prioritizing people movement instead of vehicle movement, and Vision Zero. The webpage for the ITS system actually touts a carbon savings of 73 pounds per vehicle using Mercer during AM westbound and PM eastbound, as if that wasn’t offset by additional traffic pouring into the corridor now and in the future. Something is seriously rotten in the state of the Muni Tower.

Whether or not traffic computers are able to squeeze 2.7 minutes for every eastbound car on Mercer right now doesn’t matter because it simply is not sustainable. SLU development is not slowing down, parking garages are not getting trimmed down, and the new state highway portal that will be opening smack dab in the middle of SDOT’s optimized Mercer corridor will not help matters.

City of Seattle Commute Trip Reduction Actuals, 2012 and 2014, with 2017 goals. (City of Seattle)
City of Seattle Commute Trip Reduction Actuals, 2012 and 2014, with 2017 goals. (City of Seattle)

That’s not to say that things aren’t moving in the right direction per se. The blunt number of jobs in SLU and Denny Triangle means that everyone simply cannot drive to work by the laws of geometry. But the area is lagging significantly behind central downtown in commute trip reduction.

The only way to speed up this process and get SLU to the exact same levels as the Center City is to stop trying to “rebalance” traffic and prioritize the modes that need to be prioritized. Ensure that transit has signal priority, that pedestrians don’t have to wait decades to cross a single street, and stop rewarding the onslaught of off-street parking construction with street space. There is only one direction for SLU to go if it is to continue being a model for a 21st century tech hub. The sooner our department of transportation gets that, the better off we’ll be.

Title image credit: Concept design for the SR-99 North Portal, completely devoid of pedestrians or people on bikes, courtesy of the Washington State Department of Transportation. 

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Ryan Packer lives in the Summit Slope neighborhood of Capitol Hill and has been writing for the blog since 2015. They report on multimodal transportation issues, #VisionZero, preservation, and local politics. They believe in using Seattle's history to help attain the vibrant, diverse city that we all wish to inhabit. In December 2020, Ryan started a three-month stint as editor of Seattle Bike Blog.

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Kathy Dunn

The Mercer Mess should have been in a tunnel. We could fix that by putting a lid on it for people walking and biking to use. Fairview definitely needs a pedestrian overpass across Mercer. There’s no way to cross Mercer on the east side of Fairview.


Unfortunately it still wouldn’t fix the fact the interstate is just an ongoing catastrophe and will continue to be until we offset it will a legitimate and extensive move to alternate modes. The simple fact is, we could pave the whole city before we found an amiable solution for *car traffic*. They don’t work in a city, the sooner American realize this and get over it, the sooner we can start building some real solutions.


Adron put it succinctly on the Mercer tunnel question.
“a legitimate and extensive move to alternate modes”

On record at City Hall: The Seattle Circulator Plan
(electric ETB system reconfiguration downtown plus)


i cross fairview / mercer and a lot of the issue is cars stopping prematurely for pedestrians

dont get me wrong. i dont want so many cars. and i dont want cars hitting peds

but a lotta traffic in the middle lanes to i5 would be diminished if other peds waited 1-3 more secs of the gratuitous light timer to let cars into a lane, away from the middle

obviously a better solution is less cars but i doubt that will happen.

peds, look and observe. let cars pass now and again so red/green light transitions are smoother during this awkward time. drivers, be more assertive. dont sit in the middle of mercer and fairview for 1 ped. they will prob stop walking if you just GO.

im so sick of having to wave cars over into their lane just bc theyre too timid … and their timidness ends up holding up a whole row going eastbound. lol

edit: saw comment below about skybridge for peds. that would be super useful!

Warren Trout

At least when the streets are gridlocked, maybe us pedestrians can walk around without waiting for the signal


“…it’s exactly what happens near our at-grade light rail stations on Martin Luther King Jr Way S where pedestrians can sometimes wait 10 minutes for a walk signal that grants permission to walk a few feet.”

What? Really? I have never noticed that though admittedly I don’t travel down MLK every day.


It might not actually be 10 minutes, but it is excessively long and extremely unreliable when trying to catch the light rail. Missing it means the trip just got 10 minutes added to it. Which is pretty damn unacceptable if we’re aiming to make transit actually competitive and powerful in its strengths.

Jenny Parker

Why isn’t there a light rail stop in SLU? Seems like that would be a big help in reducing the amount of street traffic…

Mike Carr

Traffic is bad for both cars and pedestrians on Mercer. Parking is bad around SLU. Construction is a constant at SLU. The demand to pass through the Mercer Corridor is increasing dramatically. Your answer is to stop the efforts to “rebalancing traffic” and ensure that transit has signal priority? Not a good solution. Start thinking about ways to improve throughput East and West on Mercer. Goal is to move the traffic. Remove choke points at both ends of Mercer, remove some turn lanes from North South traffic on to Mercer, Remove the Street Car, create pedestrian skybridges across Mercer. lots of things they could do. Sonics in SoDo, Need to make decisions which improve East and West throughput.


What idiotic drivel. Remove the streetcar? One streetcar during peak hours carries as many people as many cars, and far more people per unit area.

Mike Carr

not if the streetcar is empty

Matt the Engineer

I haven’t looked at ridership data since at least last year, but back then they had as high a ridership per mile as Link. Of course, with Broadway opening I but they’re lower again.

The point stands though: an “empty” vehicle could mean either: 1. poor ridership (at that moment in time, in that direction), or 2. great frequency. I’ve personally been on fairly crowded SLU streetcars despite their reasonable frequency.

Matt the Engineer

Let’s see… they saw a peak of 1578 daily rides per mile. Average weekday on Link per mile (weekday is skewed higher, but it’s the data I can easily find) was 3243, so quite a bit higher now that it’s expanded. That said, 1578 daily riders per mile isn’t nothing.


skybridges would be dope!

Joel Hancock

As a daily pedestrian commuter on Dexter crossing Mercer I can attest to the crossing time reduction. I like many simply ignore the pedestrians signals crossing Mercer and rely on traffic lights for crossing.