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Northgate bike/walk bridge would offer huge benefits, but faces challenges

Map from SDOT
Map from SDOT

A bridge over I-5 connecting Northgate Mall and the planned Northgate light rail station to North Seattle Community College would offer immense benefits to the neighborhood and ridership for the transit line. But it’s not going to be easy.

First, the problem: There is no way to cross I-5 between 92nd St and Northgate Way (effectively 110th St). And since Northgate Way is not at all bike-friendly, the closest I-5 crossing that is not terrifying on a bike is 117th St. That’s a remarkable 25-block barrier without a safe way for people to bike, all in the midst of a rapidly-growing neighborhood. Even without a light rail station, the bridge is needed.

For someone on foot, walking to the new station would require traveling 16–20 extra blocks if there were no bridge. That is enough to discourage a huge number of trips and would essentially leave the station stranded on the edge of a giant parking lot.

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But building the bridge will not be easy or cheap. SDOT’s Art Brochet, who is in charge of outreach for the project, presented at Wednesday’s Seattle Bike Advisory Board meeting and explained the biggest cause of bridge challenges: The freeway is elevated above the street level, and highway standards require the bridge to be pretty high above the freeway surface (for oversized vehicles, etc).

Basically, that means the bridge would have to be more than 60 feet above 1st Ave NE. At a five-percent ADA-compliant grade, that’s a couple city blocks worth of ramp just to get to the street. For an idea of how high up the freeway is, here’s a view from 1st Ave via Google Street View:

Screen Shot 2014-02-07 at 12.19.54 PM
Who in the world thought this was a smart way to design a freeway?

Brochet mentioned that a cargo-sized elevator might be considered instead of a ramp, and he went to the SBAB meeting in part to gauge reaction to that idea. He also pushed back against the idea that the bridge could cost $16-18 million, as a draft study estimated. He put the price more in the $25 million range.

I-5 damages and divides many Seattle neighborhoods, but the design in Northgate is particularly awful. Unfortunately, this means even fixing the problem a little bit will cost a lot. That’s not a reason not to do it, though. Walkability and bikeability in the area won’t get any better unless we do something about it.

So it seems to the the decision about what kind of bridge to build relies largely on cost comparisons. If a cargo elevator design proves to put the project within budget range, then maybe that could be a good option.

But maybe this is also an opportunity to build a mini-wonder, an icon of Northgate that reconnects the sometimes isolated neighborhood both literally and symbolically. Imagine spiraling or swooping ramps connecting the new station to the towering bridge. It could be pretty impressive.

Either way, the $5 million Sound Transit has pledged to the project (matched by Seattle) is dependent on the project finding the rest of its funding before the end of 2015. If funding is not secured by then, the plan is to spend that $5 million on other biking and walking projects in the area instead.

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31 responses to “Northgate bike/walk bridge would offer huge benefits, but faces challenges”

  1. mike archambault

    Dare I suggest a bike & pedestrian tunnel under I-5?

    1. Tom Fucoloro

      I actually have an email out to project folks asking if a tunnel had been considered. I’ll update when I hear back.

      My guess is that a tunnel would cost even more than the bridge, but maybe not? And maybe the better grade would make it better enough to justify the cost? I would usually think that tunnels are kind of creepy, but the I-90 tunnel is great and feels safe even at night.

      1. Brian

        Bertha’s not busy these days, maybe we could get a tunnel on the cheap. It would be large enough to fill with cafes, small shops, etc., with a bike/pedestrian path down the middle. Paint the ceiling a nice blue and you could imagine Paris in springtime…

        whoa, started dreaming there.

  2. Stephen

    A spiraling ramp would work. There are several on the RSVP route in suburban Vancouver.

  3. bill

    Any ramp has to have gentle curves. Not tight spirals. Not the hairpins on the bridges over Aurora at N 155th St and again at Westminster Way. Planners need to plan for all bikes — including tandems, recumbents, and cargo bikes, that can’t make super tight turns.

    Elevators are the better option for a bridge. A tunnel would be the best option.

  4. Kate Martin

    I concur that an underpass (at 100th?) would be well worth investigating. We talked about that when we did the Open Space 2100 charette back in 2005. Perforating the I-5 barrier was a priority. Big long ramps are really not that accessible even if the grades are technically compliant with ADA. I think the solution needs to serve people with mobility impairment which can mean flat areas to traverse instead of ramped and shorter distances. It would be great if the underpass could be used by emergency vehicles and perhaps bus transit as well as the grid is really missing there in that long stretch between 92nd and 110th and reconnecting it a bit would be useful.

  5. scott

    I believe the Northbound lanes of I-5 are higher in elevation then the southbound lanes so that tunnel couldn’t just go straight across at the elevation of 1st. It’d have to go down at a diagonal and then back up at a diagonal. This would create another ramping condition but underground. Not to mention the challenge of digging a tunnel under I-5 while semis drive overhead.

    For the tunnel to be feel safe there would need to be constant activity within it, but I’m not sure that area is going to receive as much traffic as I-90.

    According to the below link, the light rail tunneling in the Central District cost $540 million per mile. Not that a tunnel here would be exactly the same but at that rate a 500′ tunnel is gonna cost you $54 million.


    1. bill

      Whoa. The CD tunneling is twin tunnels 21′ in diameter. Cut the cost in half for one tube, scale down to say 12′ diameter for a bike/ped size tunnel, and you get $15 million. It probably would not actually be that cheap because the design and equipment costs won’t scale down exactly with the size of the tunnel. But as a back of the envelope estimate this makes a tunnel look feasible if we’re talking $25 million for a bridge.

      Maybe someone can find out what the I-90 bike tunnel cost?

      1. Tom Fucoloro

        The I-90 bike tunnel was sort of free. They happened to have some space left over at the top of the highway tunnel, so they made it into the bike tunnel. They didn’t dig it for bikes, so cost would be hard to compare

      2. The problem here is that you’d literally be tunneling through the support structure of I-5. I’m not really sure what that consists of — I assume most of it is just an embankment, but I don’t know for sure. Anyway, most of the expense is making sure the freeway doesn’t collapse. Urban freeways: the thief that keeps on taking.

        Anyway, I agree with Kate Martin that if we try to build a tunnel it should be a bus tunnel allowing Metro routes like the 40 and 16 (and probably also 345/346) to serve both NSCC and Northgate TC without circuitous or congested routings), with an ample bike/pedestrian component.

      3. bill

        You’re right, a bus tunnel is a good option. That would open up funding from Metro and increase the base of political support.

      4. Glenn in Portland

        Tunneling under something built on fill isn’t too bad these days. They have a technique that they use where they freeze the fill material with a freezing solution, which turns the surrounding fill into a substance as hard as rock. They can then safely tunnel under it just like they tunnel through rock, install concrete tunnel sides and walls (or steel), and then unfreeze the fill material.

        I think the closest place to Seattle they have done this so far was at The Dalles, Oregon:
        I don’t remember the exact cost, but I do remember it really wasn’t that bad.

  6. asdf2

    If we’re going to build a bridge, it needs to be accessible by stairs, not just a ramp. Ramps are certainly better than bikes, but for pedestrians unencumbered by strollers, etc. (and there will be plenty of them), a direct staircase shaves off a considerable distance, making for a much faster trip.

  7. JB

    What would really be sweet is if I-5 got Boulevarded from Southcenter to Lynnwood, with at-grade crossings for bikes and pedestrians. Let the traffic that needs a limited-access 60 mph highway go up the eastside on 405 and not through the heart of Seattle. I hope I live long enough to see that happen.

  8. Eric

    For crossing I5 it seems the investment should go into expanding Northgate Way between Roosevelt and Meridian to support bikes and pedestrians. The road is bike and pedestrian hostile right now as Tom notes, but there’s no reason it needs to be if you are going to spend 25 million. Also, a lot of goals could then be met, including connecting pedestrians at the mall with the Target / Best Buy complex, and making the entire commercial corridor of the mall area bike and pedestrian friendly.

    Here’s the existing Terrain / Bike Map:

    Here’s the Google Street View of the underpass:

    1. Vince Slupski

      Northgate Way seems much farther from the transit center than 92nd St, and there’s no safe way to bike to it. If a bridge or tunnel direct from the transit center proves too expensive, maybe 1st Avenue from the transit center to 92nd Street could be improved; maybe even closed to traffic or kept as one-way? Bike lanes, shelter for pedestrians, stairway, signage, etc. I served on the Northgate Mall expansion citizen advisory committee, and the mall has sadly done exactly what we expected: not invested a dime in pedestrian improvements along 1st Avenue.

      1. Tom Fucoloro

        Thanks for the history, Vince. The good news is that they are on it: A protected bike lane is planned for 1st Ave south of the station, then a multi-use trail is planned north of the station.

      2. Eric

        My main thought here is that improving pedestrian and bike access for the shopping center and surrounding commercial area should be as high a priority as improving access to the transit center. All those people that arrive at the transit center need to get to work, neighborhood people need to go shopping, and people at the mall and in the commercial offices need to get around. Just getting from Target to the mall is a mess right now.

        So instead of drawing a big bulls eye around the transit center and rating everything that way, I think a more constructive metric would be to highlight areas of density and bike / pedestrian friendliness in getting between those locations. Given that scheme, my sense is that improving Northgate Way would serve more people and reduce more trips. It would also help with costs by eliminating the need for an entirely new crossing that’s not practical because of the terrain. The pathway between the community college and the transit center would be lengthened, but that blow could be softened by having the new bike / pedestrian path be a separated pathway on the south side of Northgate Way as it goes under I-5.

      3. Tom Fucoloro

        I agree, Eric, that a safer Northgate Way would have huge value to both the station and the neighborhood as a whole. Unfortunately, that doesn’t seem to be on the table at the moment. It’s not even noted in the draft Bicycle Master Plan, a 20-year plan. That doesn’t mean a strong community effort couldn’t get it on the table…

        But even if Northgate Way were improved, I still think the bike/walk bridge is a good investment that would also increase access to the mall.

      4. RossB

        Improving Northgate Way for bikes and pedestrians would be nice, but would only be a marginal improvement compared to a new bridge. On one side of the bridge is a transit center. On the other side of the bridge is a community college. On the other hand, on one side of Northgate Way is a parking lot, on the other side is, uh, McDonalds? As a bike route it would be a nice change, but for walking the improvements would be almost meaningless.

      5. Eric

        It’s not about McDonalds, it’s about the large office complexes at the corner of Northgate way and Meridian. It seems to me that the whole commerical area should be upgraded for pedestrians and cyclists instead of focusing the money on a megaproject that just connects 2 points.

        If a cycle track was added on the south side of Northgate Way then it would be easy for bikers to go from the transit center, up to Northgate Way, under I5, and then south to the community college on Meridian- a total of 1.5 miles of flat cycling. It would also be safer as the route would be well traveled at all times, and many millions less since it’s just a matter of widening an underpass (or not even- you could just cut into the embankment on the left to make room).

  9. biliruben

    Much of the I-5 elevation is just the Southbound lanes, and there is already a wide, 2-lane tunnel with a broad shoulder (perhaps the reason for the elevation?) to provide access to the express lanes at 102nd.

    Perhaps 10 feet of that tunnel could be re-purposed for bike/ped and then limit the tunnel to just transit (cars that want Northgate access can just use the mainline), then use the large grassy area between the Southbound lanes and the express lanes for a ramp and stairs up to a bridge. Then the bridge wouldn’t need to be nearly as high or long, because Northbound and the express lanes are much lower and not nearly as wide as the entire highway.


    It would take some thought and creativity, but it might work.

    1. The orientation of that roadway makes it, necessarily, a very indirect route for anyone trying to access the future Link station from west of I-5 (especially NSCC), which is one of the main rationales for building the bridge. Also, unless you’re intending to build a vehicle bridge over the western span of I-5, this only really provides transit access to Northgate from the express lanes and from the south, a need that will diminish once Link is built. Meanwhile the need for local transit access to Northgate from west of I-5 and from the north will grow, and its efficiency will be more important. Northgate may become less of a transfer hub from the north after a station is built at 145th, but will continue to grow as a retail and office hub, and add a significant number of residents. Routes like the 16, 40, 345, and 346 (local corridors west on Holman, north and south on Meridian) need to be optimized on a time frame relevant for this kind of project, not the 41 (express to/from downtown), whose days are numbered.

      1. biliruben

        I wouldn’t say VERY indirect, a bit indirect, sure. a few hundred foot detour sure beats an elevator, however. At least on bike.

  10. transitwonk

    There are several pedestrian bridges over I-5 from Everett to Tacoma. They seem to be little used. The one in south Tacoma is a huge span, far above a giant expanse of pavement, and I have never seen anyone on it. I have always felt walking on a bridge above a freeway is kind of unpleasant. Given that I-5 near Northgate already towers over the surrounding landscape, the climb to and descent from a pedestrian bridge would be forbidding.

    I much prefer a grade-level tunnel. It should be for pedestrians and bikes only. Don’t delay its construction another decade or two by insisting it should be a full-fledged road. There are a million examples all over the country of pedestrian tunnels under roads. You don’t need to use a fancy drill; just dig it and reinforce it. I can’t be sure but I’m fairly certain the I-5 embankment is merely dirt dug out of the borrow pit/lake on the NSCC side. Make it wide and well-lit and thousands will use it every day.

    A bridge would probably be more interesting to build and pretty to look at, but are we building something people will use or just lining contractors’ pockets?

  11. RDPence

    The I-5 ped/bike crossing doesn’t need to descend to 1st Ave. It should terminate into the Northgate Link Station mezzanine, a good 20 feet higher, substantially easing the grade issue and shortening the length of the ramp.

    Thank of it like the ramp from the airport garage to the Airport Link Station mezzanine. It provides direct access to rail transit, and easy ground access through the station for people not getting on the train.

    1. Tom Fucoloro

      This was also a topic of discussion. There was strong support for having it connect directly to the station, but it will also have to have a way down to street level. The station will not be open 24 hours, and it will not open for years after the bridge is constructed (according to current schedules).

      1. RDPence

        24-hour access through the mezzanine is a design challenge, not a deal-breaker. And if the I-5 crossing gets built first (I’m skeptical…), then build a temporary ramp down to the street. Or better yet, coordinate the construction schedules so the crossing does not open before the station does.

  12. Elbe

    A tunnel makes all the sense in the world. There are many modern and relatively inexpensive ways of boring a tunnel. If fallible memory serves me well, a new tunnel (culvert) for fish was installed under I-90 in Issaquah in the last few years.
    If it were big enough, it could include a daylighted portion of Thornton Creek that is currently carried in pipes under I-5.

  13. RossB

    >> Even without a light rail station, the bridge is needed.

    Absolutely. This article suggests that $25 million is a huge amount of money. Compared to a lot of infrastructure, it isn’t. The Westlake Streetcar costs twice that much (and is a lot more expensive to maintain). It isn’t clear to me that the streetcar has saved any money over buses that run (or used to run) on that same route. On the other hand, this bridge would save several trips a day for Metro. There would be no reason for buses to go from one side of the freeway (by the transit center) to the other (by the community college). From a transportation standpoint, it would be a huge improvement. Imagine you live at Thornton Place but work at the school. How do you get to work? Walk? Maybe, but it is a long walk (around twenty minutes). Bike? Sure, but that little hill will make you sweaty, so unless the folks at the school don’t mind, you have to factor in time for a shower. Most likely you are just one of many who drive to work (and brag about how easy a commute you have). With a bridge you either walk (ten minutes at most) or bike (probably less than five minutes depending on how long it takes to lock up your bike).

    It’s not just the school, either. There are plenty of clinics and hospitals on one side, and housing on the other. The transit center exists now, and would benefit immensely from this bridge. Add in the effect the train will have and 25 million is a bargain.

    Speaking of money, the waterfront changes will cost hundreds of millions of dollars. This is outside the cost of the new tunnel (and replacing the seawall). I’m not sure about the details, but I can’t help but think that we would get more per dollar by building this bridge.

  14. tor5

    I was on the Northgate Stakeholders advisory group for the Thornton Place development and can tell you that the Northgate Mall rep was hostile toward any idea that didn’t funnel cars to the mall parking lot. He scoffed at bike lane suggestions. He even opposed better NG Way crossings to Target and Best Buy because they were mall “competitors” (yes, he said that). I don’t recall that he was opposed to the I-5 overpass idea per se, but we should be aware that these are the kinds of narrow yet powerful voices we’re up against.

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