Magnolia Bridge Planning Study

Updated: July 16, 2019

What’s happening now?

In 2017, we launched a planning study and analyzed four alternative transportation scenarios, weighing factors such as environmental impact, ease of mobility and access, cost, construction duration and impact. Please continue reading our web page to learn more or read the study in its entirety.

Last month, we hosted a community engagement meeting to share the planning study results and answer questions. View the boards from the meeting. 

So, what’s next?

With cost estimates spanning from $190M to $420M, bridge replacement and alternative options considered in this study far exceed available Seattle Department of Transportation funds without significant outside investment from our State or Federal partners.

First, ongoing maintenance and inspections of the Magnolia Bridge continue in coordination with the Port of Seattle. We perform regular maintenance, frequent inspections and 24/hour monitoring to ensure safe use of the Magnolia Bridge. That doesn’t change.

Second, the Levy to Move Seattle funds a ten-bridge study to help us assess and manage roadway structure maintenance needs and maximize future investments. The Magnolia Planning Study was the first of the 10 assessments to be completed. The studies are a part of our effort to better understand the size of Seattle’s maintenance backlog, which requires long-term attention. We’ll be launching the Ballard Bridge Planning Study later this spring.

Lastly, we’ll continue to work with the community and elected officials to be creative in examining funding opportunities for the Magnolia Bridge. We’ll also be launching the Ballard-Interbay Regional Transportation system study pending confirmation of state funding.

For additional details about how the study was conducted and how community input was considered visit the Project Library.

Project Overview

Fulfilling a Levy to Move Seattle commitment, in 2017 we launched a planning study to identify route alternatives for the 90-year-old Magnolia Bridge that meet the needs of the community, update the bridge replacement cost estimate, and create an emergency transportation plan for unexpected closures.

Currently, there are four bridges to the Magnolia neighborhood, the Magnolia Bridge, W Dravus St, W Emerson Pl and Fort St Bridge. The study area included the Magnolia Bridge and W Dravus St and analyzed four alternative transportation scenarios, weighing factors such as environmental impact, ease of mobility and access, cost, construction duration and impact.

Magnolia Bridge Planning

Emergency & Short-Term Planning

As our city and regional partners continue to examine potential mobility solutions for Magnolia, we remain committed to maintaining Magnolia Bridge safety by conducting regular maintenance and frequent inspections in coordination with the Port of Seattle. We perform 24/hour monitoring to ensure safe use of the Magnolia Bridge. Ongoing maintenance work includes managing spalling and delaminated concrete, as well as performing spot repairs.

Part of our planning study included an emergency bridge closure transportation plan in the event of a major earthquake or other event that makes one or more of the bridges unusable. The intention is to consider the safety and resilience of mobility into and out of Magnolia in the event of a catastrophic earthquake. The short-term focus in the event of an unexpected closure would be on W Dravus St and W Emerson Pl, two bridges that have received extensive repairs in the past few years.

The Study Development Process

Over the past 2 years we briefed community organizations, worked with a stakeholder group, hosted drop-in sessions and launched an online survey to inform neighbors of the planning study, to understand their mobility and access needs, and to gather input on alternative options to consider along with replacing the existing bridge. View a timeline of our study development process and community engagement efforts.

Community Engagement Results

Throughout the process we received a lot of valuable input. Here is a snapshot of how we received it.

  • 4 drop-in sessions
  • 277 drop-in session participants
  • 94 written comments
  • 18-day online open house
  • 186 online alternatives survey participants
  • 200 online open house comments

What We’ve Heard

  • Majority of community members want the bridge to be replaced
  • Of the three possible alternatives, Alternative 1 a new Armory Way Bridge into Magnolia and a new Western Perimeter Road to Smith Cove Park/Elliott Bay Marina ranked highest (continuing reading to learn more about the alternatives studied)
  • Many did not feel W Dravus St could be improved enough to support additional trips if the Magnolia Bridge was no longer available

How Input was Used

  • Added the 2006 bridge replacement into the planning study and updated cost and travel data for it
  • Supported a regional task-force with Councilmember Sally Bagshaw and the 36th Legislative Delegation. The State’s House Transportation Budget includes $700,000 for the Ballard-Interbay Regional Transportation System Plan Project
  • Provided a report identifying the major maintenance needs and planned transportation improvements for the Interbay Corridor in response to a Statement of Legislative Intent for the 2019-2020 budget

Study Process

Building on work completed during the 2006 Magnolia Bridge Replacement Project we worked with the Stakeholder Work Group and a team of consultants to analyze different components to create alternatives for analysis.

Study process diagram

Initial Screening Criteria:

  • Maintain access to Smith Cove waterfront and improve connection between Magnolia and the Smith Cover waterfront
  • Must be grade separated from the BNSF Mainline railroad tracks
  • Maintain or improve access to Terminal 91 (T91)

Technical Screening Criteria:

  • Traffic operational need
  • Geometric feasibility

Alternative Analysis Criteria:

  • Mobility and connectivity
  • Cost estimates
  • Environmental impacts
  • Implementation characteristics
  • Community support

As a result , four alternatives, including replacing the existing bridge, were evaluated.

 Magnolia Bridge Planning Alternative 1  Magnolia Bridge Alternative 2
Magnolia Bridge Alternative 3    Magnolia Bridge Alternative 4

 

Once the alternatives were selected, evaluation occurred in three phases.

Step 3A: Quantitative Analysis of Alternatives Among Different Routes

We analyzed and compared the alternatives based on a variety of criteria including their estimated cost, mobility and connectivity, environmental impact, community support, and implementation characteristics (such as the relative impact and length of construction). See a matrix showing the results of this analysis.

Step 3B: Assigning Weight

Each of the five main categories was assigned a weight, as a percentage, to reflect how critical each category is to the decision-making process.

30% estimated cost, 25% mobility and connectivity, 15% environmental impact, 15% implementation characteristics, 15% community support

The study ranked Alternative 1 (Armory Way Bridge) highest with Alternative 4 (2006 Bridge Replacement) and Alternative 2 (Dravus St Bridge) ranked in 2nd and 3rd place respectively with less than one-point difference in their overall weighted scores. View the overall weighted scores and ranked alternatives for each alternative.

Step 3C: Sensitivity Analysis

To test and verify the results of the study, a sensitivity analysis was conducted to understand how changes in the assigned weights might affect the ranked results. A series of different weighting scenarios were explored, each emphasizing a different focus. See a summary of the results of the sensitivity analysis.

A sensitivity analysis of the scores indicated that variations in weighting of the criteria could significantly impact these results.

Project Library

For more project background information, please refer to the following documents or visit the Magnolia Bridge Historical Project Library.

Transportation

Greg Spotts, Director
Address: 700 5th Ave, Suite 3800, Seattle, WA, 98104
Mailing Address: PO Box 34996, Seattle, WA, 98124-4996
Phone: (206) 684-7623
684-Road@seattle.gov

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The Seattle Department of Transportation (SDOT) is on a mission to deliver a transportation system that provides safe and affordable access to places and opportunities for everyone as we work to achieve our vision of Seattle as a thriving, equitable community powered by dependable transportation.