The new 520 bridge is now open to cars, but the Seattle side of the project is still a long way from completion. Pedestrians and cyclists have another year to be able to use the bridge to get between Seattle and the Eastside as the pedestrian bridge only extends as far as the floating bridge portion, which doesn’t fully connect to Seattle.

One big aspect left to be started is the “Montlake lid”, a cap on a segment of the freeway at the 520 interchange with Montlake Boulevard. This project has a great deal of potential, providing added green space where there might have otherwise been open freeway.

Montlake: Seattle’s Other Freeway Lid

Recently, the Washington State Department of Transportation (WSDOT) has released a series of concept illustrations for the entire west side corridor, including the new design for the newly remade Montlake Boulevard. Its cross-section schematics of the street are too large to include all of it at the same time, which is the first big red flag.

One half of the new Montlake Boulevard. (WSDOT)
One half of the new Montlake Boulevard. (WSDOT)

Yes, that’s five lanes in the northbound direction. And the southbound direction has four lanes.

Southbound Montlake Boulevard (WSDOT)
Southbound Montlake Boulevard (WSDOT)

So that’s an increase of three total lanes over the freeway. But that’s not even the worst part.

WSDOT’s drawings that were released to the public do not include the widths on any of the lanes, but if you are thinking they look pretty big, then you’re correct on that as well. We were able to obtain an internal document that shows the widths of the lanes, and that’s the truly terrifying part. Note that this is a city street, not directly part of the freeway project.

Screen Shot 2016-07-06 at 10.21.41 PM
Draft working copy of the Montlake overpass design. (City of Seattle)

Contrasted with the current configuration:

The current Montlake at 520 intersection. (Google Maps)
The current Montlake at 520 intersection. (Google Maps)

The City of Seattle’s draft right-of-way improvement manual has no place where lanes wider than 11 feet are necessary. The twelve and even thirteen feet lanes here are literally off the charts—highway designs on city streets. Wider lanes encourages higher speeds when exiting the freeway.

The City of Seattle Draft Right of Way Improvements Manual on Arterial Lane Widths (SDOT)
The City of Seattle Draft Right of Way Improvements Manual on Arterial Lane Widths (Seattle Department of Transportation)

Montlake Boulevard is also not considered a major freight route on Seattle’s update to the Freight Master Plan, currently under review, so wide lanes built to handle high volumes of truck traffic are not necessary here, at least from the City’s perspective. So the big question is whether they will stand up for the new standards that they have determined are best for the city’s streets.

Another major question still outstanding is the issue of bus priority. The blueprints show bus-only lanes through the interchange, but the cutout drawings show buses in HOV lanes—on city streets. This is going to be the biggest chokepoint in the “high capacity corridor” being studied for upgrades to the current Route 48.

WSDOT will also be collaborating with the City of Seattle on the I-5 interchange at Roanoke Street, another instance where it will be very important to ensure that Seattle design requirements are followed and not WSDOT highway standards. There are signs, however, that things might be starting to change at the State’s department of transportation. They recently introduced a concept called practical design, which appears to favor multimodal corridors over traditional state highway projects from purely a cost-savings standpoint. Perhaps folks at WSDOT are realizing they may need to come to grips with their massive maintenance backlog and stop running headlong into new projects without considering their long-term plan for sustainability.

In the meantime, we should send them the message that Seattle doesn’t need highway-level street designs on our arterials.

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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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Walter Crunch

I see an opportunity for a major roundabout.

Walter Crunch

Wow, way to create a massive intersection that will ATTRACT major traffic. Nice!

Brian Schend

Since they’re building this massive lid anyway, why not put a 2-lane roundabout on top, all the ramps meeting at a single intersection instead of 2? Wouldn’t that solve all the problems?


Yes, please! Seattle needs more roundabouts to solve the absurd density of close intersections.

Brian Schend

Reminds kind of like the S 38th interchange in Tacoma


I don’t understand why there are two left turn lanes in the northbound direction. That implies huge numbers of people from Montlake, all trying to get on the freeway heading west. I just don’t see it. There aren’t that many people in Montlake doing that. One justification for the dual turn lanes is that it allows for a shorter light cycle. But that really isn’t an issue. That light doesn’t cause a backup. Either the ramps are backed up (onto the freeway) or the bridge itself is the bottleneck. There is also no need for HOV access in that direction. There are no bus routes that go that way (nor is it likely there ever will be).

Other than on Montlake itself (for the 48), the only area where they need the extra lanes is UW to the east side. So that means westbound 520 to northbound Montlake as well as southbound Montlake to eastbound 520. The first seems to handled just fine with this proposal. I’m not sure about the second. Looking at it some more, though, I think I understand what they have in mind (although I would like to see more detail).

I’m guessing that after you cross the bridge southbound, the lane that is added (the far right lane) becomes a BAT lane. Only buses and cars headed westbound on 520 are allowed to use it. The hope is that this ramp isn’t that crowded (I don’t believe it is metered, so that may be a reasonable assumption). Once past that on-ramp, the lane is bus only. The inside lane is the bus only lane, not the outside one (as it is now).

That seems reasonable, but I’m not exactly thrilled by it. I think it is quite an assumption to think that traffic headed westbound on 520 (towards I-5) won’t be a problem, and backup onto the ramps.

If I remember correctly, there are going to be eastbound ramps to 520, fairly close to 24th. These will replace the Foster Island ones. If that is the case, then I could see bus lanes be carved out quite nicely. You basically take the left lane after the bridge. This makes for smooth sailing for the 48. Then you have a left turn lane for buses, followed by a bus lane on Lake Washington Boulevard (it would be widened over the freeway) and then a metered ramp with an HOV lane entrance. I know that is a lot of hand waving — I would need to see more details on this before I could tell if it would work.

In any event, the first priority for this should be bus access. Of course it would be nice to have this be a pleasant space, but it isn’t pleasant right now. The part over the bridge is ugly and will probably always be ugly. Make it as wide as need be (to handle the buses, the bikes and the cars) but I wouldn’t be too concerned about making this pretty.


It’s a tricky issue; on the one hand, it’s a city street. On the other hand, it *is* technically a highway, SR-513.

Since bridges end up as choke points, I’m not surprised by the desire for lots of lanes. However, if it’s going to get lots of lanes as a highway, perhaps it should also get pedestrian/bike bridges like some wide highways do!


The other glaring problem is there is no uniform standard 9.5,10,11,12,13,14,15.

How does that hold you are apply science here. Its sounds like you are just going for the biggest lane you cram into the space.


Most of the lane width variation comes down to turning movements, geometry, lane use, and available right-of-way. “Standard” is 11′ for straight travel lanes and 12′ for turning lanes to accommodate vehicle swing (a UPS or moving truck, for example). Metro likes wider lanes so buses have room to maneuver, especially on curves (hence that 15′ lane w/ a painted buffer). 9.5′ is a legacy width from Seattle’s old streets. Wider curbside lanes are typical to accommodate buses, turns, and sometimes bicycles.

Even though there are standards, they’re simply a starting point and engineers change things based on need.


Lane widths over 12′ are never warranted. 10′ is the standard for safety. 11′ is okay when major freight of bus movements are involved.


Sure, make them 10′ wide and the buses will just take two lanes like they do on the Aurora bridge. That would work great!


11′ lanes for buses Jason – READ. The interchange needs dedicated bus lanes throughout. Buses with 50 people should never be stuck behind 5 SOV cars.

Dan Ryan

The transit implications are a lot broader than Route 48. Every bus on SR 520 will go through here.

Ott Toomet

Any idea how will the traffic light cycles look like? I like the idea that sidewalk are more straight than in the current configuration (no deed to cross the separate turn lines) but I am concerned the lights may be unfavorable for walkers/cyclists.


The number of lanes is definitely surprising, but you have to consider that they’re really looking at how to reduce the abhorrent backups along montlake in the afternoon by ensuring traffic funnels effectively through the interchanges to the highway. The current setup generates terrible backups along Montlake whichg I would argue is a far worse situation. That mvoes some dirvers into the surrounding neighborhood streets who try to beat some of the backup at unsafe speeds.
In my opinion, adding some lanes around the interchange to improve the flow of drivers onto the highway is a better tradeoff to calm some of the surrounding streets and neighborhood.


Same type of engineering that created the massive Mercer St. project in South Lake Union.




I won’t defend the lane width, but I think the # of lanes is defensible given that there is going to be huge volume of people turning at this interchanging trying to get on to 520 during rush hour. Without multiple dedicated turn lanes, there is a risk of cars waiting to turn left spilling into the GP lanes, causing havoc on traffic flow.
Further, most of the foot & bike traffic will be going north south, where there are broad, dedicated walkways away from the stroad.. If you are trying to catch a bus & need to cross Montlake, you can cross at the cross walks right before and after the lid, which are several lanes narrower – no one is crossing the street where it’s at 11 lanes wide.

The switch from bus-only to HOV lanes is odd. Hopefully that’s just a quirk on the illustration.


Thanks for the post. I am terrified of the Montlake interchange, it is absolutely massive! Nine lanes wide is insane, like they’re predicting every car in Seattle is going to pass through here every day. And what looks like almost a complete lack of a safe crosswalk network.

Simon Cooke

That’s because they’re putting a bus interchange in at UW.