Cascadia Says Tunnel Still Makes Sense

Letter to the Viaduct Stakeholders Advisory Committee

November 20, 2008

Alaskan Way Viaduct Stakeholders Advisory Committee
c/o Alaskan Way Viaduct and Seawall Replacement Program
999 Third Ave., Suite 2424
Seattle, WA 98104

Dear Committee:

Cascadia Center of Discovery Institute wants to express its continued support for the Committee’s work to find new alternatives for replacing the Alaskan Way Viaduct. As the Committee enters the final stages of its deliberations, we wanted to also make sure that the advances in and practicalities of tunneling technology are fully and fairly appreciated.

In March, you received from us a letter explaining our view that a deep-bored bypass option deserves serious consideration as a workable, effective option for replacing the aging Viaduct. That letter and its attachments articulated the reasons that this option could be the best solution. We also shared examples of tunnel projects around the world. Since then, and with the assistance of ARUP, a leading global engineering and consulting firm, we have more closely analyzed worldwide tunnel projects. Those findings are summarized in the charts and comprehensive study attached to this letter and titled, “Large Diameter Soft Ground Bored Tunnel Review.”

Cascadia Center is a strong supporter of surface transit options, and we have worked on issues such as bus rapid transit, streetcars and passenger ferries. Surface transit options appear to be a feasible first step, but the deep-bored bypass tunnel option should continue to be studied and considered as a solution for the 70 percent of vehicles now using the Viaduct for freight and bypass purposes. For the sake of Western Washington’s economic viability, and to realistically plan for a growing population and capacity issues, the tunnel should be further vetted. A deep-bored tunnel stands the best long term chance of helping the region fully utilize Highway 99 and the Interstate 5 corridor. Further, a key advantage of the deep-bored tunnel is that it can be constructed without disrupting the waterfront and its businesses.

As indicated in the attached material, advances in tunnel technology – especially with regard to diameter increases—continue at a steady pace. As noted in the report, “the completion of two highway tunnels beneath the Yangtze River in Shanghai, China in September this year represents another milestone….” Those tunnels have a 51ft. diameter and “will carry three lanes of vehicular traffic and a transit line in each direction.” That region’s soil consists of sand and clay. We strongly encourage your review of the most recent Cascadia-ARUP report, which offers these key conclusions about tunnel boring technology:

  • Capable of increasingly large diameters – up to 51ft – and increasingly common in use and proposal for worldwide and U.S. highway traffic;
  • Becoming more commonly used and of larger diameter (Moscow, Russia-based ZOA Infrastruktura has penned a deal to acquire a 62.3ft. diameter tunnel boring machine);
  • Able to successfully and safely navigate weak ground and in significant groundwater pressures

The Cascadia-ARUP report also addresses cost comparisons for several projects around the globe. Although there are multiple and variable considerations to weigh when estimating costs for large infrastructure projects, Table 2 and Figure 4 of the report “suggest a typical cost range per mile of a twin bore project of approximately $200M to $700M” indicating “that construction costs for tunnel projects larger than a two mile Alaskan Way by-pass tunnel are somewhat less than previously published estimates.” Importantly, the report emphasizes that whole-life costs of a tunnel make more sense than other options. From the report: “The life span of tunnels have historically been longer than that of viaducts, with the BNSF tunnels in Seattle being over 100 years old against the existing Alaskan Way Viaduct and SR-520, which are reaching the end of their life span after approximately 50 years.”

Based on our research and analysis, there seems to be no reason not to give full consideration to the deep-bored bypass tunnel option. As a means of lowering cost, addressing capacity, offering the least amount of disruption to the city and its inhabitants, controlling storm-water runoff into the Bay, and reducing emissions, a tunnel option makes most sense. A deep bored tunnel also has the benefit of increasing Seattle’s natural asthetic by allowing views (from neighborhoods such as Magnolia and Fremont) and allowing South Lake Union and South Queen Anne to be “knit” back together. The issue of capacity is a vitally important consideration, and it is important to remember that studies show that the majority of vehicles using the Viaduct are passing through, not trying to get to, the city.

Our letter from March addressed a variety of legitimate issues—Seattle’s substantive history with tunnels, capacity and freight concerns, and environmental matters—that are part of the debate. As reference to those issues, we’ve also included the entirety of our March submission to the Committee.

Finally, in 2007, we held an international tunneling symposium that brought international experts in to discuss advances in tunneling technology and possibilities. We would look forward to hosting another session in early 2009. Such a session would be important because there are other projects in the area with a strong interest in how deep-bored tunnels can be used. Most importantly, a session in early 2009 could be designed to answer these specific questions: specific costs for a Seattle tunnel; possible construction duration schedules based on whether one or two moling machines were used; budget scenarios, including mitigation; and, the impact on the city under this scenario.

Thank you again for your important work. As the Committee enters the close of its deliberations, we urge strong, fair consideration of the inland deep-bored bypass tunnel. We look forward to answering any questions you may have and stand ready to help in any way we can.

Bruce Agnew
Policy Director
Cascadia Center of Discovery Institute
208 Columbia Street
Seattle, WA 98104
(206) 292-0401 x113 direct; (206) 228-4011 mobile

Further information:
Letter to Stakeholder Advisory Committee
View the full report commissioned by Cascadia here

These files are large and may take several minutes to download for slower internet connections

Bruce Agnew

Director, Cascadia Center
Since 2017, Bruce has served as Director of the ACES NW Network based in Seattle and Bellevue, Washington. The Network is dedicated to the acceleration of ACES (Autonomous-Connected-Electric-Shared) technology in Northwest transportation for the movement of people and goods. ACES is co-chaired by Tom Alberg, Co-Founder and managing partner of Madrona Venture Group in Seattle and Bryan Mistele, CEO/Co-Founder of INRIX global technology in Kirkland. In 2022, Bruce became the director of the newly created Pacific Northwest Economic Region (PNWER) Regional Infrastructure Accelerator. Initial funding for the Accelerator has come from the Build America Bureau of the USDOT. PNWER is a statutory public/private nonprofit created in 1991 by the U.S. states of Alaska, Idaho, Oregon, Montana, and Washington and the Canadian provinces of Alberta, British Columbia, and Saskatchewan and the territories of the Northwest Territories and the Yukon. PNWER has 16 cross-border working groups for common economic and environmental initiatives.