The West Seattle Bridge closure represents huge problems for the people and businesses in the community and while potential remedies are challenging they are also opportunities to make improvements and prepare for the future.

The cracks that led to the closure while first observed in 2013, changed in length and character so fast that the Seattle Department of Transportation was left with no options. They had to close the bridge. SDOT has installed a  monitoring system in the meantime including everything from crack space monitors to listening devices to give them a real time understanding of the bridge’s condition. An interagency task force has put together a comprehensive plan to address what happens should a catastrophic failure occur. They don’t think it’s likely but a plan like that is necessary.

So what are the choices SDOT might make regarding the present status and the future of the transportation corridor to West Seattle?

The West Seattle Bridge Task Force (comprised of 12 to 15 community members and leaders) soon to be announced by Mayor Durkan is faced with looking at everything from repair, to remediation and replacement.

So what do those options look like?

Repair

The mainspan may have seen what is called “creep” in which concrete shrinks over time, causing the pre-tensioned steel cables inside the girders to become slack. When the bridge was built, holes were left to allow the later addition of steel to provide more tension and strength. That’s one potential part of a fix.

SDOT has said that carbon fiber wrapping is something they might explore. This form of concrete girder repair uses what is called Fiber Reinforced Polymer that is applied in one of two methods. After preparing the surface by grinding, and filling to achieve a smooth surface an epoxy is applied and the material is applied in strips, then coated again. During the process holes can be drilled in the structure and the carbon fiber material can be literally stuffed in and then fanned out on the surface. After epoxy is then applied again, much higher levels of tensile strength can be achieved.

SDOT has some experience with this having done seismic retrofit work on the Cowen Park Bridge in Ravenna.

There have been some suggestions that some kind of steel "exo-skeleton" be added to the most damaged sections but it's worth noting that the center span already weighs some 4600 tons and that 80% of its load is it's own weight. So steel, outside the bridge is likely to add quite a bit of weight.

First up however is the replacement of the neoprene bearing at Pier 18 that when working properly allows the bridge to move slightly in response to temperature variations and load. It’s currently “locked” meaning it has failed. When it “unlocks” it sends shockwaves along the entire length of the bridge according to SDOT and could make the existing cracks worse. SDOT has hired Kraemer North America to make the repair. That will mean precision removal of the concrete around the bearing, then building a form, and replacing the concrete and bearing with a new one.

Also in the current plan is the construction of a shoring or support structure under the bridge. That is currently under consideration but will likely mean building a kind of bridge below the bridge. No contract has been awarded for that shoring work but the bulk of $33 million required will be the construction of that shoring system.

Assuming the bridge can be repaired, these determinations will likely be made after the shoring system is in place and a firm hired to do the work. 

What about demolishing the bridge? That process would likely be difficult and time consuming and involve marine cranes as sections of the bridge are removed, and then lowered to a barge. The shoring system would keep the existing bridge sections intact as it is removed.

 

Remediation

With the bridge out of service until at least some time in 2022 what has been done and what could be done to make getting around easier or better. The Highland Park Action Coalition asked SDOT about this and got these responses.

Highland Park Way SW and SW Holden St Intersection 

• Request for a left-hand turn signal for turning onto SW Holden St from northbound lane on Highland Park Way SW 

◦ Status/update: We installed a temporary traffic signal at this intersection and it’s not currently possible to add a left-hand turn signal to it. We are, however, sharing this feedback with the team designing the permanent traffic signal scheduled to be installed in 2021. 

• Request for extra traction on uphill southbound lane on Highland Park Way SW 

◦ Status/update: The Highland Park Way SW and SW Holden St Safety project team will evaluate high friction surface treatment. This treatment has typically been done where crashes have occurred when roadway conditions were slippery. 

• Request for separate green signals for pedestrians and drivers in the northwest corner of the intersection  

◦ Status/update: We installed a temporary traffic signal at this intersection and it’s not currently possible to add these features to it. We are, however, sharing this feedback with the team designing the permanent traffic signal scheduled to be installed in 2021. 

Turning from arterial streets onto SW Holden St 

• Request to see painting and/or signage to prohibit blocking of the intersections  

◦ Status/update: Because these treatments have limited effectiveness and high maintenance costs, SDOT is focusing on more effective tools, many of which are below and will also be reflected in the neighborhood traffic plans we are preparing.  

Traffic calming in the neighborhood Status/update: SDOT is developing a neighborhood-specific plan to evaluate concerns like these and should have drafts ready as soon as two weeks.) 

• Request to add more traffic calming throughout the neighborhood 

◦ Status/updated: We are responding to cut-through and safety service requests as we receive them from community members and based on observations by our traffic engineers in the field. We are also working to keep the arterial street network moving efficiently to encourage its use instead of the residential system some choose to use for longer trips. 

• Request to add calming near Sanislo Elementary School 

◦ Status/update: In summer 2018, SDOT crews completed improvements for the Sanislo Elementary Safe Routes to School (SRTS) project, making it safer and easier for kids, families, and neighbors to walk and bike to Sanislo Elementary School through the intersections of SW Orchard St and 18th Ave SW and SW Myrtle St and 18th Ave SW. Question for HPAC: Can you clarify specific locations of additional traffic calming you would like SDOT to focus on?  

Requests for dedicated turn signals  

• 16th Ave SW and SW Holden St  

◦ Status/update: SDOT can do a restripe here consistent with the Your Voice, Your Choice project that was selected for construction this year. It does not provide a turn signal, but provides a dedicated place for people to wait for a gap in approaching traffic.  

• 16th Ave SW and SW Roxbury St 

◦ Status/update: This is a complicated request that would require channelization changes with additional impacts. We can get back to you on this idea as we engage the neighborhood on the collaborative neighborhood traffic plan that we are developing.  We will bring a draft to your next meeting.   

• 8th Ave SW and SW Roxbury St 

◦ Status/update: We are not currently budgeted to add this signal to the existing mast arm. 

Traffic signal adjustments to address traffic backups   

• 16th Ave SW and SW Holden St 

◦ Status/update: In progress. SDOT is planning to make this adjustment by the end of May. 

• Delridge Way SW and SW Holden  

◦ Status/update: Timing changes were made in the last couple of weeks and we will continue monitoring this intersection. 

• SW Orchard St and Delridge Way SW 

◦ Question for HPAC: Can you provide more specific information on what signal adjustments you’d like to see at this intersection?  

• 8th Ave SW and SW Roxbury St 

◦ Status/update: We are updating the controller on this signal in the next two weeks.  

SW Roxbury St, Olson Pl SW, and 4th Ave SW 

• Request for additional marked crosswalks 

◦ Status/update: We’re making safety improvements for people walking at the SW Roxbury St and Olson Pl SW intersection as part of Seattle’s Vision Zero program. This intersection is in both the City of Seattle and unincorporated King County and requires cross-jurisdictional collaboration. The West Seattle Bridge team is in contact with the Roxbury/Olson intersection project team to share HPAC’s request for expedited implementation. We will update you when we learn more about the timeline.  

King County Metro Route 131 

• Request for bus only lane on Highland Park Way SW  

◦ Status/update: We will have further details in our next response to HPAC on May 19. We are collecting traffic counts here to see if this is feasible with the changing travel patterns since the bridge closure. 

• Request to adjust signal at Highland Park Way SW and SW Holden St for bus priority 

◦ Status/update: This request will also be evaluated as part of the Highland Park Way SW and SW Holden St Safety project.  

• Request to increase Route 131 service  

◦ Status/update: We shared this idea with Metro, and they are engaged in a transit planning exercise for West Seattle. 

Pedestrian path on the east side of Highland Park Way SW after the SW Holden St intersection 

• Request to consider widening the path to allow for more use  

◦ Status/update: The Highland Park Way SW and SW Holden St Safety project team is exploring options on widening the path to make it more attractive for pedestrians and bikes. We will have further details in our next response to HPAC on May 19. 

• Request to clean moss off from path  

◦ Status/update: SDOT will clean this pathway in the next two weeks.  

West Marginal Way S  

• Request for better bike lane marking at the intersection with Highland Park Way SW   

• Status/update: We will have further details in our next response to HPAC on May 19. The Highland Park Way SW and SW Holden St Safety project team will be looking at ways to widen the existing path (east side of Highland Park Way SW) and will also look at markings to enhance bike visibility to the widened path.  

• Request to fill potholes and fix road deterioration near the railroad tracks   

◦ Status/update: SDOT has driven and regularly monitors the detour routes, including West Marginal Way S. As part of this process, we identified and prioritized pothole improvements along those routes. The location where West Marginal Way S and the railroad meet is maintained by BNSF Railway. We have notified BNSF of these issues.  

• Request for two lanes northbound at the intersection with Highland Park Way SW   

◦ Status/update: Due to the geometry of the intersection, this would require removing a southbound lane approaching the intersection and would have unintended consequences.  We are not moving forward with this recommendation.  

Cut-through traffic on local streets  

• Request to add signage on local streets to help with cut-throughs   

• Request to add stop signs at unmarked intersections   

• Request for east to west monitoring, specifically at 35th and Delridge  

• Request to make some streets one-way to help with cut-through traffic   

• Request for a stop sign at 11th and Kenyon   

◦ Status/update: Cut-through traffic is a complicated issue. Any attempts to eliminate or discourage cut-through traffic may solve the issue on one street, but most likely will have secondary, unintended impacts on adjacent streets within the neighborhood. As a result, evaluating cut-through traffic requires a comprehensive neighborhood traffic study to quantify the problem, develop neighborhood-wide solutions and build consensus. We can get back to you on this idea as we engage the neighborhood on the collaborative neighborhood traffic plan that we are developing.

SDOT has also made changes at the Delridge Way SW, Chelan Ave SW, and W Marginal Way intersection. Delridge Way SW got a bus-only lane northbound from SW Andover St to Chelan Ave SW. The east leg of the intersection (westbound W Marginal Way SW) was changed from 2 through lanes to 1 through lane and 1 left-turn lane. The west leg of the intersection (Chelan Ave SW) was converted from 1 shared left and through lane to 1 through lane 1 left-turn lane.

Ferries and other marine solutions

The question of ferries has come up in many discussions as well but it’s important to understand the numbers. A foot ferry like the Doc Maynard costs around $7 million. It can carry 289 people. The ferries are administered through King County, not the City of Seattle. The bridge at peak capacity carried 100,000 vehicles per day plus 25,000 transit riders. How many ferries do you think it would take to make a difference? Even adding an additional 20 runs a day would only carry 5780 people. Beyond that, the Colman Dock in downtown Seattle still being remodeled, has limited dock capacity for more ferries. Adding another ferry from Vashon and the Kitsap Peninsula direct to downtown might help a little more but even then, the time and volume of traffic the bridge could carry dwarfs the ferry solution.

It's even been suggested a return to the early days of the "Mosquito Fleet" which prior to the construction of the original West Seattle Bridge, brought people to West Seattle and points south. But existing marine traffic in the form of commercial ships, barges and more make that idea impractical.

 

Replacement

As it now appears there are these options:

1. Repair the bridge and return it to limited service while an alternative is being considered, funded and built. Limited service might mean a reduction to fewer lanes, putting weight limits on the kind of vehicles that can use the bridge, and/or installing traffic control systems (much as they do on some freeway on ramps) to limit the number of vehicles on the bridge at any one time.

2. Tear down the existing bridge and build a combined traffic, transit and light rail bridge on the line ST3 suggests north of the two existing bridges which would mean ANOTHER 140 foot high clearance type structure that would have a 110 ton train on it.

3. Build a cut and cover trench approach on either side of the river and install an Immersed Tube Tunnel, creating approach ramps (as they did in the construction of the 520 bridge) that switch over when ready. The tunnel could have six lanes plus two lanes for light rail. No tunnel boring machine is needed. Just a modification of the existing ramps.

4. Tear down the existing bridge and build TWO new bridges, one for traffic and transit and another just for light rail which presumably COULD be another SWING or DRAW bridge to the north of the existing bridges. If it's a swing bridge it will have to be enough away from the existing swing bridge for clearance. If it's a draw bridge it will mean either marine traffic or rail traffic will have delays. 

Of those options the lowest cost, and according to engineers the safest is likely the tunnel, though the cost of soil remediation and land acquisition is unknown at this time.

So the questions of what is the best way forward remain both open and challenging. As has been acknowledged by Councilmember Lisa Herbold and others, it’s possible a solution could get some funding assistance from the state or federal government, even though this is technically a city bridge. The 1980’s construction was partially funded with federal money. It’s possible, though it wouldn’t be popular, to institute a toll, much like SR 99 and 520 and parts of I-405 now utilize to offset the cost of a replacement.

 

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