Let's build world's first submerged floating tunnel
Special to The Times
"The significant problems we face cannot be solved at the same level of thinking we were at when we created them."
- Albert Einstein
Never was this saying more appropriate than when applied to Seattle's transportation woes. Yet we continually revisit predictable antidotes for our problems — widening Interstate 5, widening Interstate 405, widening the Highway 520 floating bridge.
Because we both work as consultants to the construction industry, we admit we find highway projects fascinating. But while driving, we don't want to be creeping by such projects so slowly we could conduct engineering inspections from the car.
It's time for a new paradigm. Time to once again put the Puget Sound region on the map by being innovative. After all, we have the Space Needle, the Monorail, two new sports stadiums and two floating bridges. Let's add to our reputation as a world-class destination city, and simultaneously resolve some of our transportation problems. Let's build the world's first submerged floating tunnel.
What is a submerged floating tunnel (SFT)? Also known as an Archimedes bridge, an SFT is a buoyant structure that floats below the surface of a body of water and is held in place by anchors to the bottom of a lake or sea.
The concept is attractive for many reasons. Recreational boats and shipping have unrestricted access for navigation. By floating below the surface, somewhat like a submarine, the tunnel is not exposed to the havoc created by wind on the surface of a body of water. No doubt many Seattle commuters can readily relate to the times when the 520 bridge has been closed due to high winds and waves.
And in terms of aesthetics, it's hard to beat the concept of a structure that isn't even visible. Although bridges can be architectural and engineering wonders, the view from a new shoreline park made possible by an SFT, with only boats and distant mountains on the horizon, would win the contest hands down. In Norway, serious consideration has been given to SFTs for strait crossings in the fjords to avoid detracting from the scenic wonders. The same holds true for Lake Lugano in Switzerland, where a study was undertaken to keep motor vehicle traffic and transit away from the lakeshore.
There are other technical considerations that favor SFTs. Traditional subsurface or sea-bottom tunnels require more surface infrastructure for entry and exit than an SFT because tunneling has to begin much farther from the lakeshore. Steeper entrance and exit gradients result in larger fuel requirements and more air pollution from vehicles climbing uphill. Because an SFT is placed at much shallower depth, these problems are largely avoided. For deep channels in particular, an SFT may be the most realistic option. And it's an option not limited to vehicular traffic. SFTs can be designed to accommodate light rail or other mass transit as well.
So why haven't any SFTs been built? Number 1, they are not cheap. For example, an SFT across Lake Washington has an estimated cost of $3 billion. But the expense compared to other options seems excessive only if you fail to take life-cycle costs and tax-base considerations into account. Once you add in the maintenance costs for both the wind- and wave-battered surface structures and the complex mechanical systems needed to accommodate boat and ship traffic, as well as the loss of tax base along shoreline properties inherent to other solutions, the cost gap for an SFT lessens considerably.
Of course, there are significant safety considerations for a submerged floating tunnel, and no doubt failure of an SFT would be catastrophic. But, have you ever wondered what would happen if a bridge were to fail? The potential consequences are virtually identical.
Probably the main reason no SFT has yet been built is because no one has wanted to be first. Our departments of transportation, consultants, engineers and contractors are somewhat risk averse, and often with good reason. But we're really not talking rocket science here. There already are literally hundreds of non-floating tube tunnels in sea bottoms all over the globe that carry vehicle and transit traffic, and numerous offshore oil platforms that are engineering marvels. The same technology that enables us to make use of these structures is easily adaptable to SFT construction. So perhaps public perception is the real opponent.
When we used to mention the SFT as an option to the 520 widening, the response was often, "I wouldn't dare drive through one of those." Rather than argue the point, we are reminded that options are the true key to solving our transportation woes.
Let's put the SFT under the floating bridge. Then traffic will self-define. Those people not afraid to drive through the SFT will do so, leaving the others on the floating bridge to contend with less traffic. And we could incorporate transit in the SFT, or on the floating bridge, so kids who want to go to a concert in Seattle from the Eastside don't have to pester mom and dad.
This technology is being given consideration by the National Science Foundation and the first U.S. workshop on SFTs is being held in Seattle this weekend.
One day, we may travel on light rail or maglev from SeaTac to Seattle utilizing a Lake Washington SFT, or on high-speed rail from Olympia to Tacoma to Seattle in a Puget Sound SFT. The possibilities stretch the imagination.
Mark Liebman, left, is director of special projects for AMEC in Kirkland; Dr. Teresa Taylor Zeitler, right, is project manager at SubTerra, Inc., in North Bend. They are co-chairing the Workshop on Submerged Floating Tunnels tomorrow and Sunday at the Westin Hotel in Seattle, in conjunction with the North American Tunneling 2002 conference. The workshop is free and open to the public. Further information is at www.ussft.com.