Is Deep-Bore Tunnel Best Hope To Replace Viaduct?

The search for a practical successor to the Alaska Way Viaduct has taken our region on a roller-coaster ride. Two high-profile alternatives — a new aerial structure and a cut-and-cover tunnel — crashed when their cost in disruption plus construction proved prohibitive.

The issue became so hot that the architects of Proposition 1 didn’t even put a viaduct solution in their complex and costly package, which nonetheless suffered defeat at the polls in November.

Amidst political turmoil, two alternatives have moved steadily along — the surface street option and a deep-bore bypass tunnel. Each has been nurtured by proponents more interested in making the case for their approach than in attacking others.

Moreover, the two approaches appear compatible since they would minimize disruption to the waterfront and downtown while connecting these two iconic parts of Seattle.

The bypass tunnel assists the surface street option by providing a capacity solution for the 60,000 vehicles that use the Viaduct each day as a through route, taking this load off the design of a surface street plan. Some strategists are already talking about a tunnel finance plan that includes funds which could be applied to surface street and transit amenities.

On Dec. 14, the Cascadia Center for Regional Development convened a seminar featuring global and regional experts on deep-bore tunneling. Several key topics were discussed before an audience of over 100 attendees.

The seminar moderator was Gary Lawrence, Urban Strategies Leader for Arup Consultants. He began by asking if there is a “solution set that more than adequately addresses” a range of issues that brought previous approaches to grief.

A roster of experts responded. John Reilly, a leader in the International Tunneling Association, asked, “Why elevated? Why surface? Why underground? Open this question up to the possibilities and then narrow the options to what is achievable, affordable and acceptable.”

Alan Dyke, managing director for the high-speed rail route between London and the English Channel, said a tunnel under London was chosen because disruption and environmental mitigation requirements of a surface route through the city would been excessive. He added, “We picked a route that actually promoted redevelopment of derelict sites in the city.”

The Paris A86 beltway automobile tunnel holds a similar lesson. Jeff Hall is vice president of Cofiroute, a subsidiary of Vinci, one of the largest construction firms in the world and builder of A86. Hall said Paris went through alternatives — surface roads, a cut-and-cover tunnel — and rejected them due to a quality of life issue: Protection of the Parisian greenbelt. “A deep-bore tunnel was the only way to do this while adding capacity.”

Bob Park is president of Acciona Canada, whose parent firm was lead contractor on the Madrid M30 project, another beltway auto-tunnel. He reported, “Madrid chose a tunnel as the best way to reconnect neighborhoods, reduce emissions, regenerate its riverbank and develop new leisure areas.”

Seattle’s tunneling history is more extensive than many residents realize.

Red Robinson, lead geo-technician for locally-based engineers Shannon & Wilson, described several of the more than 100 tunnels in Seattle that total over 65 miles in length. The 64-foot wide Mount Baker Tunnel on I-90 is the world’s largest soil ridge tunnel.

Seattle City Council transportation committee chair Jan Drago added that in recent years, “We’ve been building deep bore tunnels in Seattle — Third Avenue, Beacon Hill, Brightwater.”

In opening remarks, Drago noted that “tunnel technology has changed significantly if not dramatically since we started searching for solutions to the viaduct.”

Dick Robbins heads The Robbins company, a Seattle-based designer, maker and operator of tunnel-boring machines (TBMs). He said “big advances in tunnel technology are the result of steady progress that makes tunneling cheaper, faster and safer.” In Red Robinson’s words, “New technology makes the impossible possible.”

One key element, Lawrence said, is that “the scale is increasing, to solve problems that smaller-bore tunnels couldn’t solve.” Reilly confirmed this. “Only now are we getting to TBM diameters that can handle traffic and emergency lane needs.”

Jack Brockway is senior vice president for the USA division of Herrenknecht, a German firm that is the recognized world leader in TBMs. He reported that “each machine is designed for the kind of ground it is going through, with a unique mix of cutter heads for the geology. It is custom-built and assembled in the shop or at the job site. Big TBM’s are refurbished, modified and re-used.”

Reilly noted that “Politics is often focused on initial capital cost, but we must look to total life-cycle cost. Tunnels cost more to build but less to maintain. They last a lot longer than elevated structures or surface streets.”

For this reason, Reilly believes tunnel construction should be funded through mechanisms that recognize long-term benefits as well as higher initial cost.

Drago commented that the Seattle City Council “does this with utility investments but not transportation. Life-cycle cost analysis should be part of this decision.”

The seminar steered clear of debates over precise cost estimates for a Seattle tunnel but offered illuminating examples. Dyke noted that the 23-mile long London rail tunnel was built in 19 months and cost $75 million per mile — about half what historical experience would suggest. “One reason was early involvement of contractors through price competition and performance incentives.”

But Dyke added that “a holistic assessment of costs, risks and opportunities is essential. London’s bored tunnel project would not fly on transport benefits alone. Property gains and environmental improvements create value that should help contribute to project costs.”

Lawrence agreed that real estate improvements can help pay for the project. “In Asia, some rail projects are paid for entirely by the sale of air rights,” he noted. The analogy for Seattle would be the development gains that would come from removing the viaduct.

Another source of financing is to partner with pension funds held by unions, or even public employee funds such as California’s CALPERS. “Transportation projects and tunnels around the U.S. have union pension funds in their financing package — and we get the construction work,” said John Littel of the Northwest Regional Council of Carpenters.

Littel described how the building trades unions combine pension funds with equity investment in the Northwest and elsewhere, working with investment firms to identify infrastructure projects.

Drago concluded the session by observing, “A tunnel is part of a larger system, not an isolated project. How does a solution for Highway 99 fit into our transportation and transit system?” The Cascadia Center’s seminar helped move the deep-bore bypass tunnel along as a viable option that could combine with a surface street strategy to put Seattle in the “post-viaduct” era.

Glenn Pascall is a Senior Fellow at Cascadia Center and helped organize the Dec. 14, 2007 conference on deep-bore tunneling described above.