A totally tubular approach to the Highway 520 mess

Smart urban areas are learning to free up scarce land and improve the environment by using innovative design for their transportation corridors. Given the right conditions, placing major roadways underwater or underground can be cheaper and better for the environment than the old, above-ground model. In particular, use of cost-effective, shallow submersible tubes can benefit taxpayers, travelers and the communities through which they travel.

An opportunity to use this technology is available to Seattle. The state plans to rebuild the Highway 520 bridge. On Seattle's side of Lake Washington, 520 could be placed in shallow submersible tubes. While it is too early to estimate the cost of using submersible tubes, some early estimates indicate they could be built for less than an above-ground structure with identical traffic capacity.

Many citizens living along the 520 corridor worry that the state's proposed 520 replacement, a massive above-water structure, would have significant adverse impacts on the Arboretum, University of Washington, Pacific and Montlake transportation corridors, Roanoke Park and the environment as a whole. These impacts include noise, air, dust, water and visual pollution, and disruption of archaeological remains.

Concerned residents from Laurelhurst, Madison Park, Montlake, Roanoke Park and North Capitol Hill have proposed an alternative plan: a pair of one-way submerged tubes that would lie on the floor of Union and Portage Bays, connecting with Interstate 5 and surfacing at the eastern edge of Laurelhurst and Madison Park, where they would connect with the state's new floating bridge.

The submersible tube is not new technology. Submersible tubes were recently used to connect Boston with Logan Airport and traverse Chesapeake Bay. Submersible tubes have also been used extensively in Japan and the Netherlands.

Typically, the tubes are precast in 300-foot sections of steel and reinforced concrete, barged into place, submerged on a shallow bed of rock and gravel, and connected by sealing and welding. Prefabricating the tubes makes them approximately 25 percent less expensive than the state's proposed Portage Bay and Union Bay viaducts.

A tube could easily accommodate general-purpose and high-occupancy vehicles, mass transit, pedestrians and bicycles, depending on its size. The I-90 tunnel through Mount Baker is a good local example.

The state's bridge plan, with entering and exiting traffic concentrated in one area, would create significant traffic congestion at that location, currently proposed for just south of Husky Stadium at Northeast Pacific Street and Montlake Boulevard Northeast.

By contrast, submersible tubes could be engineered to allow neighborhood traffic to enter and exit at several smaller intersections, rather than at one huge interchange. Innovative traffic controls could reduce commuter use from outside the neighborhoods.

An underground link could also directly connect Highway 520 and the South Lake Union and Seattle Center neighborhoods. This would require a mile-long tunnel under North Capitol Hill from Portage Bay to the intersection of Fairview Avenue North and Eastlake Avenue East. It would remove 520/South Lake Union/ Seattle Center traffic from Interstate 5 without increasing neighborhood impacts.

The environmental benefits of submersible tubes would be substantial. Archaeologically important Foster Island would remain untouched. Noise from, and unattractive views of, a large new bridge and interchange would be eliminated. Water quality would be improved with efficient collection and treatment of automobile runoff. Air pollution would be reduced through scrubbers on the tubes' air ventilation systems. Dust from the freeway would be eliminated. Portage and Union bays would be restored to their natural state. Neighborhoods bisected by 520 could be made whole again.

In preparing beds for the new tubes, contaminated soil in Lake Washington could be cleaned up, dramatically improving the area's ecosystem. Finally, land in areas now marred by the Highway 520 "spaghetti" corridor could be converted into housing or parklands. Property values would not be depressed (as with the proposed bridge), but would be significantly improved, thereby strengthening the local tax base.

Modern municipalities are accommodating the automobile with solutions that reduce impacts on the environment and reclaim scarce land. Technologies such as submersible tubes merit serious consideration by our transportation officials.

Theodore Lane a Roanoke resident, is an economist and traffic-noise-impact consultant. Bill Mundy a Madison Park resident, is a real-estate economic, market and valuation research consultant.