State, King County, City Should Keep Tunnel Option

Letter to Governor, King County Executive, Mayor

December 3, 2008

Re: Maintaining Sub-Surface Options to Replace the Alaskan Way Viaduct

Dear Governor Gregoire, Mayor Nickels and King County Executive Sims:

We concur with the jointly signed letter you received this week from the Greater Seattle Chamber of Commerce, the Downtown Seattle Association, and the King County Labor Council: Sub-surface options should continue to be included for consideration to replace the Alaskan Way Viaduct. As you know, the December 31, 2008 deadline for a decision on the Viaduct is fast approaching. We applaud the efforts of the Viaduct Stakeholders Advisory Committee during the last year and thank you in advance for your thoughtful consideration of sub-surface options.

As expressed by the Chamber, the DSA and the Labor Council, “we see no reason to exclude sub-surface options.” That said, based on our analyses of alternatives over the last several years (including an attached recent cost comparison study which we hope you will review) the Cascadia Center of Discovery Institute would take this sentiment one step further. Of the sub-surface options, a deep-bored bypass tunnel, combined with surface transit improvements, represents the best alternative for the replacement of the Alaskan Way Viaduct. We have long supported surface transit options, including bus rapid transit, streetcars and passenger ferries. Surface transit options can be a part of a short-term solution. But lasting, long-term solutions can best be found in sub-surface scenarios. Importantly, as the Chamber, DSA and Labor Council have shared, sub-surface options “match up well against the Guiding Principles.”

The letter signed by the Chamber, the DSA and the Labor Council points to the clear economic benefits of a sub-surface option, including regional economist Glenn Pascall’s 2006 study that “identified up to $2.7B in regional economic benefits.” Those benefits are realized in part from increased economic activity and higher property values downtown as a result of a tunneled structure. Mr. Pascall articulated further benefits for a bored tunnel in the attached March 16, 2007 op-ed in the Puget Sound Business Journal titled, “Bored By All Those Viaduct Choices? Think Again.” We encourage you to review his op-ed.


Cascadia Center has conducted our analysis of deep-bored tunnels because of our interest in assuring that the monumental decision about replacing the Viaduct is made with full consideration of our community’s long-range challenges and opportunities. These include economic impacts, opportunities to build toward a fully functioning and interconnected transportation system, and the full life cycle costs of the investment. Over the last several years, Cascadia has convened a panel of international tunneling experts in Seattle and commissioned a series of independent studies from ARUP, a global engineering and consulting firm. We have sought to compare the relative costs (and review remarkable advancements in technology) of deep-bored tunnels around the world. Attached is our latest communication to the Viaduct Stakeholders Advisory Committee highlighting the results of our work.

There are significant disparities between the estimates of the state’s technical team and the actual costs of scores of tunnel projects already in place around the world. We encourage you to closely examine Table 1, “Completed large bore tunnels” from our November 2008 ARUP report, “Large Diameter Soft Ground Bored Tunnel Review.” (Note: Table 1 is also extracted and attached to this letter.) Even considering the proposed Port of Miami tunnel (at $677 million per mile the most expensive of the tunnel projects), the data indicates that the tunnel costs for the Viaduct should come in around $1.4 – $1.7 billion. The costs of the tunnels in our survey include full costs: ventilation, portals, entry and exit, life safety and roadways. This cost is significantly less than the current projection made by the state’s technical team. (Note: The $3.5 billion cost of Scenario F includes adjustments for risk, inflation, and a construction timetable that is too long. The cost of Scenario C, and the surface option, is at $900 million.) We also note that the construction timetable for the tunnel projects is less than half the 10-year construction period currently under discussion by the committee.

To further refine cost estimates, we recommend funding to engage some of the world’s leading tunneling contractors to work with the current project team and independent local consultants to advance the engineering and provide their best estimate of the costs. Considering that over $300 million has been spent on work to date, this would be a bargain for a tunnel that would serve the region for 100-150 years rather than the estimated 50 years of useful life for an elevated structure.

When the deep-bored tunnel is combined with a range of surface transit enhancements, it has other significant advantages:

  • Provides the best capacity, travel time and through-put for the 55-80 percent of traffic on Highway 99 that is by-pass or through traffic;
  • Represents the least disruption to the waterfront and downtown, since construction will occur underground and dirt can be hauled away via rail or barge while the Viaduct is still in use (Hebert’s economic impact study in November 2006 estimated the cost of this disruption at $2.2-$3 billion for each year the Viaduct was down without a replacement.);
  • Surface water runoff and air emissions could be captured and treated in a tunnel structure (through new electrostatic precipitator technology) resulting in a cleaner Puget Sound and lower greenhouse gases;
  • Alignment could run through the central downtown area rather than the waterfront- eliminating the need to replace the seawall as a part of the Viaduct replacement project;
  • Surface transportation enhancements can move ahead immediately while tunneling costs are refined and financing secured;
  • A deep-bored tunnel can be planned and built as part of a larger regional system of bridges and tunnels including SR 520, Sound Transit’s Link light rail through Beacon and Capitol Hill, and possibly a downtown tunnel in Bellevue with likely project cost-sharing and economies of scale;
  • Sale of air rights along corridor could result in financial partnerships to reduce project costs and share risk;
  • Offers the best opportunity to reconnect Seattle’s waterfront and downtown core, introduce more sunlight, open views and park and recreational opportunities;
  • New boring technology provides tunnels with up to 53 feet of diameter, allowing for three highway, transit and/or truck-only levels;
  • A “Y-shaped” tunnel configuration could provide access to the third of traffic on SR99 that heads to Ballard or Fremont along the western corridor as well as to Mercer to I-5.

Thank you for your concern about the future viability of the Puget Sound region. We’d be happy to review our data with you and answer any questions you may have.


Bruce Agnew
Cascadia Center of Discovery Institute
208 Columbia Street
Seattle, WA 98104
206.292.0401 x113 direct
206.228.4011 mobile

Further information:
Letter and tunnel comparisons sent to Governor Gregoire, Mayor Nickels and King County Executive Sims

Cascadia-ARUP Tunnel Report, Nov. 2008

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.