Blog A Deep-Bored Tunnel To Replace The Alaskan Way Viaduct

All over the world deep-bored vehicle tunnels are being built in major metropolitan regions. Paris. Hamburg. Zurich. Dublin. Madrid. Wuhan. Nanjing. Shanghai. Scroll down here to Cascadia Center’s chart titled “Supplemental Tunnel Project Data Examples” and you’ll see costs per mile range from $106 million to $580 million for deep-bored vehicle tunnels in these cities, typically of four to six lanes. The chart is part of a lengthier submission we made to the Alaskan Way Viaduct Stakeholders Advisory Committee (SAC).
That cost range is worth noting, as SAC and state consultants work through options to replace the aging and unsafe viaduct on Seattle’s downtown waterfront. There are eight alternatives now getting a closer look, and one is a slightly curving four-lane deep-bored tunnel that would run as much as 2.5 miles from South Royal Brougham Way to Aurora Avenue North and Harrison Street. Estimated costs for all eight alternatives are to be firmed up later this year. Then, after several final options are recommended by the SAC; the Governor, King County Executive and Seattle Mayor in early 2009 will give their recommendation to the state legislature, which will shortly thereafter make the final decision. It’s supposed to be an open book, right now, as to what will be the final choice.
The Seattle Times reports today that of the $2.8 billion already allocated for Viaduct replacement by the legislature, $1.1 billion has been spent or committed for downtown transit, south terminus surface work, pier stabilization, utility line relocation, and improvements to the old Battery Street Tunnel, which will stay in operation no matter what choice is made. This leaves $1.7 billion. Replacing a seawall downtown for about $400 million is required as part of Viaduct project. That money might come partly out of the state kitty or the city might cover part or all of the cost on its own.
But the deep-bore option could still pencil out.
As we’ve reported to the SAC, global experience shows that now, deep-bored vehicle tunnels are being built for $106 million to $580 million per mile. The given length of the whole Viaduct corridor is 2.2 miles. But because of slight curves in the envisioned tunnel route, let’s figure a liberal 2.5-mile length for the deep-bored tunnel. (Project refinements could actually result in a much shorter tunnel distance, but that’s not clear yet).
If the global data we’ve gathered turns out to apply – fairly closely – to costs of a four-lane deep-bored Viaduct replacement tunnel here, and the length is 2.5 miles, the price would be in the range of $265 million to $1.45 billion, almost certainly closer to the high end. If the city ends up paying for just half of the seawall replacement, the remaining funds of $1.5 billion could cover the costs of a deep-bored tunnel.
None of this assumes additional funds from High Occupancy and Toll (HOT) lanes in a deep-bored tunnel, which are eminently possible and could help offset any additional costs, such as those caused the rising price of construction materials. In use around the United States as one of several emerging “congestion pricing” strategies, HOT lanes allow solo drivers for a variable fee, while multiple-occupant vehicles and transit travel free. Travel times are guaranteed to be faster than in general use lanes; experience elsewhere shows drivers at a range of widely varying income levels use and appreciate HOT lanes as a way to get where they have to, when they cannot risk being late due to traffic congestion. An admittedly preliminary 2002 Parsons Brinkerhoff study for the state found that tolling the Viaduct would be feasible as part of a broader regional highway corridor pricing strategy, and that each million dollars raised by tolling the viaduct, net of operations, could leverage another $7 to $10 million in capital investment and $1 to $2 million in debt service.
A complementary strategy, which limits taxpayer exposure, is via risk controls built into a design-build-finance-operate (DBFO) agreement with a contractor consortium. Public costs are capped and contractor payments and penalties are pegged to meeting strict project performance goals. The often-costly disconnect between the design and build phases is minimized; exacting timelines and operations standards are instituted; and the public sector retains ownership of the property and control of tolls, fares or fees. Increasingly, this is how smart governments are stretching infrastructure dollars further.
Even without these supplemental strategies, the deep-bored tunnel option demands serious review, going forward. As we note in our cover letter to the packet we submitted earlier this year to the Viaduct SAC:

Seattle has vast experience with tunnels, both historic and
contemporary. There are more than 100 tunnels in the area, totaling over 65 miles in length. Two current deep-bored tunnel projects in the area are worth noting: the Sound Transit light rail tunnel through Beacon Hill and the Brightwater sewage tunnel….experience shows that in the long run, elevated structures wear out much sooner and require more maintenance than tunnels. Full life-cycle costs and benefits favor a tunnel over an elevated replacement…..

The Viaduct is part of State Route 99, a major regional roadway. It handles about 110,000 vehicle trips daily, about two-thirds of them thru traffic that’s mercifully zipping past downtown. With more than $2 billion in needed pavement and congestion reduction work on closely parallel, jammed Interstate 5 remaining unfunded, it’s more important than ever before to provide an adequate alternative for north-south downtown bypass traffic on SR 99. Highway pricing is being developed for the replacement of the State Route 520 Floating Bridge, possibly including the parallel cross-Lake Washington span on Interstate 90. A electronically-tolled HOT lane pilot project is already underway on State Route 167 in southeastern King County, and there’s electronic tolling on the new southbound span of the Tacoma Narrows Bridge. The long Eastside north-south corridor of SR 522, I-405 and SR 167 is a prime candidate for expanded HOT lanes, at some point in the future. Electronic tolling is already here and will continue to spread. Against this regional backdrop, HOT lanes in a deep-bored tunnel replacement for the Viaduct would encourage more high-occupancy vehicles on SR 99, and increased transit use.
The Viaduct project’s own partnership agreement signed by the governor, mayor and county executive makes clear that thru traffic flow and the economy are key considerations:

Any solution to the Alaskan Way Viaduct must optimize the ability to move people and goods in and through Seattle in an efficient manner….(and)…must sustain the city, region and state’s economic vitality.

A deep-bored tunnel will be more durable and a better investment than an elevated replacement. It will open up the downtown waterfront to green, recreational space and encourage new, carefully-vetted development beneficial to taxpayers and the economy. Unlike the so-called “surface-transit option” which would raze the Viaduct and not replace it, a deep-bored tolled tunnel would keep traffic moving, and could demonstrate innovative contracting strategies in the public interest.
Despite the vehement and visceral objections of some critics to the very idea of a deep-bored tunnel to replace the Viaduct, it deserves very serious consideration.