West Seattle Bridge Update; Capital Projects Watch List Resolution; SDOT Answers to Council Questions

Home » West Seattle Bridge Update; Capital Projects Watch List Resolution; SDOT Answers to Council Questions

West Seattle Bridge Update

On Monday, March 30th, SDOT presented an update at the Seattle City Council’s Briefing meeting, one week after the closure of the West Seattle Bridge.

Here’s a link to the SDOT Presentation; you can watch the meeting at the Seattle Channel meeting archive.

I emphasized to SDOT Director Zimbabwe the shock in West Seattle at the sudden closure, and universal support for the quickest action possible. While not to downplay the importance of the COVID-19 emergency, the bridge closure is yet another emergency for West Seattle; its importance cannot be overstated, on a peninsula with limited access points to the rest of Seattle. It carries as much traffic as the former Alaskan Way Viaduct.

In response to Council questions, SDOT Director Zimbabwe said SDOT does not yet have an estimate for how long the bridge will be closed, or the cost of repairs; he estimated 3-4 weeks before this information is available, and he said that the closure won’t be of short duration. SDOT indicated that the bridge must be shored up as a first step, before repairs can proceed. A likely option is to use carbon fiber wrap, as was used for the Alaskan Way Viaduct in the years before it was removed.

I emphasized I was willing to assist however possible, be it through championing funding, expediting any permits needing Council approval, authorizing alternative design and construction methods, or other actions. I also emphasized the need for transparency with the public moving forward.

I asked if SDOT will consider opening the bridge to limited traffic (e.g. 1 lane in each direction) before full re-opening, and Director Zimbabwe said they can consider, but depending upon the result of monitoring traffic volumes on the lower bridge.

I appreciate SDOT’s quick action to install a temporary stoplight at the intersection of Highland Park Way SW and SW Holden Street; I’d like to see similar action in addressing traffic management, which will become more difficult after the COVID-19 epidemic abates, and traffic volumes increase.

SDOT provided a timeline for bridge inspections, which the federal government requires every two years. Beginning in 2014, SDOT performed annual inspections, and noted moderate crack growth in August, 2019. Inspections in October, November and December showed ongoing growth in cracking.

On February 21st, SDOT’s engineering consultant recommended limiting the bridge to 2 lanes in each direction. On March 19, the consultant recommended closure. An SDOT engineer inspecting the bridge the morning of March 23rd recommended closing it that day.

This SDOT Blog post includes a time-lapse graphic of the growth of the cracks, and the significant expansion in March.

I appreciate the action on behalf of public safety, in particular and the willingness of SDOT Bridge Group Supervisor Matt Donahue to act quickly and call leadership from the bridge on March 23rd. However, notice should have been given to the Council and public earlier.  In the best case scenario, the Council and general public would have been notified during the last three months of 2019, when monthly inspections started; this should also have been included in the 4th Quarter capital projects report to the Council. I appreciate the Council’s Transportation and Utilities Committee Chair, Councilmember Pedersen, focusing on this issue, which is relevant throughout the city.

At the very least, I believe that the Council and the public should have been notified on February 21st, when SDOT’s engineering consultant recommended limiting the bridge to 2 lanes in each direction.

SDOT reported that any repairs that take place in the section of the bridge above the Duwamish navigation channel would trigger a requirement for Coast Guard approval, in its federal role with jurisdiction over marine waterways. That would likely add additional time to the closure.

In response to a question my office asked last week, SDOT indicated the assessment of bridge condition ratings for bridges in Seattle will be ready this week.

SDOT’s presentation also included updated information about the lower (Spokane Street) bridge.

SDOT indicated the daily capacity of the lower bridge is 20,000 vehicles, which is stop-and-go traffic.

Last week a traffic count showed 15,000 vehicles; EMT vehicles were stuck in that level of traffic.

In response to written questions regarding the use of the lower bridge overnight, when traffic is lower, and for emergency responders such as nurses, firefighters and police officers, SDOT has noted they are limiting access to emergency vehicles, freight, and transit, and has replied, “We are monitoring traffic on the Low Bridge 24-hours a day from our Transportation Operations Center.  As new traffic patterns develop, we may be able to adjust access.”

SDOT is requesting residents honor the limitations on bridge use.  If residents do not observe these restrictions, SDOT says that they will work with the Seattle Police Department to enforce them.  In addition, Director Zimbabwe seems to be suggesting that the ability of anyone to use the lower bridge could be at risk in the future, if drivers do not observe these restrictions.  “To enforce the lower bridge restrictions, SDOT Director Sam Zimbabwe said ‘we have support by the Police Department,’ along with signs, but enforcement might need to increase. So far, there’s been little or no traffic policing. ‘If we have everybody trying to use the lower bridge, nobody will be able to use the lower bridge,’ he said.”  See today’s Seattle Times article for more.

SDOT will be completing a load rating study of the lower bridge, which opened in 1991, and will inspect the bridge weekly.

In response to my question about addressing the 5-way intersection below the bridge, SDOT indicated they are using data to adjust traffic signals on a daily basis.

SDOT noted that in the fall of 2020, they plan to begin a study on the West Seattle Bridge’s remaining useful life; they noted a similar study has been ongoing regarding the Ballard Bridge. The West Seattle Bridge opened in 1984.

SDOT has a project webpage for the West Seattle Bridge, where you can sign up for updates. SDOT also posted a summary of the March 30 meeting on the SDOT Blog.

I am sending all constituent questions and suggestions to SDOT.

Capital Projects Watch List Resolution

The Council adopted Resolution 31942 I sponsored, along with Councilmember Pedersen, Chair of the Council’s Transportation and Utilities Committee. The resolution adds work related to the West Seattle Bridge to the 2020 Capital Project Watch List for enhanced reporting.

SDOT Answers to Council Questions

SDOT has answered some of the questions sent by my office and the City Council. Here’s a link to responses from SDOT so far. Below are highlights:

Has SDOT received word from the Coast Guard about flexibility re: times the bridge can remain open w/o or with limited closures?

The Coast Guard has broadcasted a notice to non-commercial vessels with a request to time transit and requests for openings during non-peak commute times. We are making a deviation request for am/pm peak close periods that, if they are not objected to by local mariners, can last for 180 days. Additionally, we can request an official rule change for a close period, but that is a 6-month process and subject to any objection from the local maritime community.

Can SDOT allow vehicle traffic on the lower bridge overnight? I have heard from more than one person whose work shift begins at 3 a.m., when traffic is lighter.

We understand the inconvenience the closure of the High Bridge poses to the West Seattle community.  In light of the current public health emergency, our top priority is emergency access to hospitals and protecting the supply chain, so we are reserving access to emergency vehicles, freight, and transit, and working with our partners at SPD, SFD, the Port, and Metro to determine the extent of the access limitations.  Detour signs are posted and SPD officers are stationed at either end of the Low Bridge to direct GP traffic away from the bridge.  We are monitoring traffic on the Low Bridge 24-hours a day from our Transportation Operations Center.  As new traffic patterns develop, we may be able to adjust access.

I have heard from several COVID-19 first responders (firefighter, ER nurse) who must leave the peninsula for work, and from an immunology researcher at UW working on COVID-19. Could the lower bridge be opened for them?

We acknowledge it is critical for doctors, nurses, researchers and first responders to get to their jobs.  At the same time, we must reserve access to the Low Bridge to emergency vehicle transporting critically ill patients.  Many people who live and work in West Seattle serve many kinds of essential functions – we need to maintain equity for all of them. The Low Bridge is currently open to essential workers who get to work by taking transit, walking, and biking. It’s also open to essential workers who need access to Harbor Island and T-5 and people using emergency vehicles and transporting freight as part of their jobs. For essential workers who are driving private vehicles, they are directed to the 1st Ave S Bridge.

Please explain SDOT’s procedures for providing information the Council regarding ongoing inspections for potential significant problems that could lead to closure of major roadways or structures.

SDOT regularly conducts inspections of bridges in keeping with Federal requirements. These inspections are programmatic in nature, and generally identify preventative maintenance and repair actions, while also tracking the evolution of the bridge structure over time. The load rating project for the West Seattle High-Pass Bridge started in 2019 indicated that the cracking problem was more serious than originally reported in the consultant study we commissioned in 2014 after cracking at post-tensioning anchorage points was first discovered in 2013. We performed an in-depth analysis through the consultant doing the load rating work. As part of this analysis we needed more accurate mapping of the cracked bridge sections near the anchorage points so we inspected the bridge via Under Bridge Inspection Truck (UBIT), interior inspections of the box girders at the anchorage points and additional exterior inspections in October and December of 2019 and again in March of 2020.  As the analysis was coming to a conclusion in March 2020 it indicated that there was a serious load carrying capacity issue with the bridge, we simultaneously noticed that the rate of cracking was increasing at a concerning rate just within the month of March 2020.  This rate of increase was unexpected compared to previous months and gave us reason to close the bridge for safety.

The closure of the bridge, while abrupt, followed SDOT’s commitment to transparency and timely communication with the Mayor, City Council and the public on all issues that will or are quite likely to negatively impact their constituents. What led to the short window of time between alerting the Council and the public and the closure of the bridge on March 23 was the rapid acceleration of cracking within an extremely short period of time.  

Please provide a timeline of SDOT’s inspections of the West Seattle Bridge that lead to this decision.

We regularly inspect our bridges. The events of the past few days is a notable example of why those efforts are critical and why we take this responsibility so seriously. During a 2013 routine inspection of the West Seattle Bridge, our bridge inspectors discovered four sets of cracks in the bridge support structure. We’ve inspected the bridge every year since then; twice as frequently as required by federal guidelines. Since then, we’ve closely monitored and managed the cracks. In 2014, we installed real-time data collection equipment to aid in these efforts, which allowed us to remotely monitor the width of existing cracks on the bridge. At this time, we also began conducting more frequent inspections and implementing best-practice maintenance and repairs. Those annual inspections did not indicate a need for repairs that would significantly disrupt standard use of the bridge. During a 2019 assessment of the bridge’s ability to carry heavy loads, our structural engineering consultant mapped the cracks in the bridge and discovered that they had grown since the previous year’s inspection. We and our engineering consultant continued to closely monitor these cracks and carry out critical maintenance by injecting epoxy into them to protect the steel reinforcements. In late February 2020, our engineering consultant recommended that the rate of deterioration made it necessary to consider traffic restrictions to ensure public safety. As we came to the same conclusion late last week, while we were drafting a lane-reduction plan and preparing to initiate conversations with City leaders and the community, our structural engineering consultant notified us that they had conducted new analysis raising larger concerns. We conducted several observations over the next few days and on Monday, March 23, we found significant new cracking. This confirmed that cracking had rapidly accelerated to the point where there was no other option but to immediately close the bridge.

(in response to a question about 2013, 2016 and 2019 changes to federal bridge load rating standards):

Federal guidelines require that bridges in the National Highway System be inspected every two years (see National Bridge Inspection Standards in 23 CFR 650C). During a 2013 routine inspection of the West Seattle Bridge, our structural engineers discovered four sets of cracks in the bridge support structure. We have been closely monitoring these cracks since then, installing real-time data collection equipment in 2014 allowing us to remotely monitor the bridge condition, and began conducting more frequent follow up inspections in 2014, 2015, 2016, 2017, 2018, 2019, and 2020.

In an unrelated process, the FHWA issued new requirements in 2013 that DOTs reevaluate all bridge load ratings by 2022 due to the growing use of heavier trucks for specific kinds of emergency response and construction vehicles. This required SDOT to re-evaluate the maximum vehicle weight that 69 bridges could safely support. We began these load rating revaluations in 2015 and started the West Seattle Bridge reevaluation in mid-2019, according to our planned schedule.

Please provide the most recent list of SDOT’s assessment of Seattle’s bridges (including ratings).

Each year Roadway Structures updates their Project Rating Criteria List based on the previous years’ bridge condition data and rating factors that prioritize local concerns including equity and transportation system impact. The 2019 Project Rating Criteria for SDOT’s bridge inventory is being updated and will be ready the week of 3/30.

Can traffic signals at the 5-way intersection at West Marginal Way, Spokane Street, Delridge Way be adjusted to better serve new traffic patterns? One constituent said they had to wait through 5 light cycles to get to Spokane Street from West Marginal during the afternoon with relatively light traffic.

We know the 5-way intersection has been a challenge even prior to the High Bridge closure. The current intersection design is intended to maintain all potential movements and separates each leg to remove potential conflicts. With increased demand on the intersection as a result of the High Bridge closure, SDOT will re-evaluate the intersection to see whether any design or operational changes can help address congestion while maintaining safe operations.

This signal is on our high priority emergency list to be upgraded so that the signal system is interconnected to our central system. This will allow for us to adjust signal timing actively based on new traffic patterns.  These upgrades also include improved detection to better facilitate new priority movements. This work will be prioritized after our work on Highland Park Way & Holden and our target is to complete it within the next 2-3 weeks.

What was the original design vehicle and what would we use today?

The bridge was originally designed for a design live load commercial vehicle designated as HS-20 (like a large commercial tractor-trailer truck but slightly less axel load than an articulated bus). Since the bridge was brought online in 1984, the size and loading of commercial vehicles have continued to increase as indicated by the much larger HL-93 design loading that is used to design new bridges today. Note that HL-93 loading is not a specific commercial vehicle type, but rather a requirement to choose the worst load combination presented by combining either an HS-20 or Heavy Tandem Trailer with a distributed lane load. The ‘93’ refers to the year that this loading type was adopted as the governing load combination for bridge load rating calculations. This load combination captures the loading of the larger articulated buses that are in use today.