Technical Memo
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Technical Memo To Wes Ducey, SDOT Project Manager Lisa Reid, PE, PMP/SCJ Alliance From: Marni C Heffron, PE, PTOE/Heffron Transportation Inc. Date: April 17, 2019 Project: Magnolia Bridge Planning Study Subject Alternatives Analysis Summary 1. Executive Summary The existing Magnolia Bridge currently serves to connect to and from Magnolia, Smith Cove Park/Elliott Bay Marina, Terminal 91/Elliot Bay Businesses, and 15th Ave W. The bridge serves 17,000 ADT and 3 King County Metro bus lines serving an average of 3,000 riders each weekday. The bridge was constructed 90 years ago and has deteriorated. While SDOT continues to perform maintenance to maintain public safety, the age and condition of the bridge structure means there will continue to be deterioration. In 2006, following a 4-year planning study; however, over the last decade, funding has not been identified to advance this alternative beyond 30% design. This Magnolia Bridge Planning Study identified three Alternatives to the 2006 recommend In-Kind Replacement option. These Alternatives, along with the In-Kind Replacement option, have been analyzed and compared through a multi-criteria evaluation process. Focusing on the main connections into Magnolia and Smith Cove Park/Elliott Bay Marina, the Alternatives identified are: Alternative 1: a new Armory Way Bridge into Magnolia and a new Western Perimeter Road to Smith Cove Park/Elliott Bay Marina ($200M - $350M), Alternative 2: Improvements to the existing Dravus St connection into Magnolia and a new Western Perimeter Road to Smith Cove Park/Elliott Bay Marina ($190M – $350M), Alternative 3: Improvements to the existing Dravus St connection into Magnolia and a new Garfield St bridge to Smith Cove Park/Elliott Bay Marina ($210M - $360M), and Alternative 4: In-Kind Replacement of the existing Magnolia Bridge adjacent to its current location ($340M – $420M). Smith Tower 506 2nd Ave, Suite 1400 Seattle, WA 98104 Office 206.739.5454 Fax 360.352.1509 scjalliance.com The multi-criteria evaluation processes focused on key metrics in five broad evaluation categories, including: Mobility and Connectivity including travel time modeling to key destinations served by the existing bridge based on estimated traffic growth in the Interbay corridor out to the year 2035; Environmental Impacts including impacts to existing land uses, sensitive areas, and natural hazards; Cost Estimates including planning-level cost estimates of construction, right-of-way, engineering, and administration; Implementation Characteristics including metrics that speak to aspects of the actual construction process and how each alternative may impact or benefit the traveling public; and Community Support including project-specific criteria related to the level of community support expressed by the public and stakeholders for each alternative during the MBPS outreach effort After considering the scores of the alternatives among all the comparison metrics and applying a sensitivity analysis to the metric weights, two options consistently performed best – Alternative 1 ($200-$350M) and Alternative 4 ($340-$420M). SDOT ♦ Magnolia Bridge Planning Study 2019-0417 | 2 of 40 2. Table of Contents 1. Executive Summary ............................................................................................................................................1 2. Table of Contents ...............................................................................................................................................3 3. Memo Purpose ...................................................................................................................................................5 3.1. Introduction ................................................................................................................................................5 3.1.1. Project Background ............................................................................................................................5 3.1.2. Project Purpose & Goals .....................................................................................................................5 3.1.3. Evaluation Process ..............................................................................................................................6 4. Description of Alternatives .................................................................................................................................7 4.1. Alternative 1 - Armory Way Bridge ............................................................................................................8 4.2. Alternative 2 - Dravus Street Upgrade .......................................................................................................9 4.3. Alternative 3 - Lower Magnolia Bridge .................................................................................................... 10 4.4. Alternative 4 – In-Kind Replacement ....................................................................................................... 11 5. Analysis Methodology ..................................................................................................................................... 12 5.1. Evaluation Criteria and Weighting ........................................................................................................... 12 5.2. Mobility and Connectivity ....................................................................................................................... 13 5.2.1. Vehicular Access (75%) .................................................................................................................... 14 5.2.2. Multimodal Mobility (25%) .............................................................................................................. 16 5.3. Environmental Impacts ............................................................................................................................ 17 5.3.1. Impacts to Adjacent Land Use (40%) ............................................................................................... 18 5.3.2. Impacts to Sensitive Areas (30%) .................................................................................................... 18 5.3.3. Impacts to Natural Hazards (30%) ................................................................................................... 18 5.3.4. Environmental Impact Analysis Results ........................................................................................... 18 5.4. Cost Estimate ........................................................................................................................................... 20 5.4.1. Preliminary Cost Estimate (100%) ................................................................................................... 20 5.5. Implementation Characteristics .............................................................................................................. 21 5.5.1. Construction Duration (40%) ........................................................................................................... 21 5.5.2. Construction Impacts (30%) ............................................................................................................ 22 5.5.3. Construction Phasing (30%) ............................................................................................................. 23 5.5.4. Implementation Characteristics Analysis Results ............................................................................ 24 SDOT ♦ Magnolia Bridge Planning Study 2019-0417 | 3 of 40 5.6. Community Support ................................................................................................................................ 24 5.6.1. Public Support (50%) ....................................................................................................................... 24 5.6.2. Stakeholder Support (50%) .............................................................................................................. 25 6. Alternatives Analysis Results ........................................................................................................................... 27 6.1. Analysis Results ....................................................................................................................................... 27 6.2. Weighted Scores ...................................................................................................................................... 28 6.3. Sensitivity Analysis ................................................................................................................................... 29 7. Conclusions ...................................................................................................................................................... 32 Appendices Appendix A – Purpose and Goals Appendix B – Component Analysis Appendix C – Travel Time Analysis Appendix D – Transit and Non-Motorized Analysis Appendix E – Cost Estimates Summary Memo Appendix F – Construction Duration and Impacts Summary Appendix G – Outreach Summary Report Appendix H – Alternatives Analysis Scoring Details SDOT ♦ Magnolia Bridge Planning Study 2019-0417 | 4 of 40 3. Memo Purpose The following memo memorializes the process, methodology, and results of the alternatives analysis conducted as a part of the Magnolia Bridge Planning Study (MBPS). The alternatives analysis represents the final step of the MBPS which was initiated in 2017. To support