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Click this map to see the SR 99, city street and transit improvements proposed as part of the viaduct replacement program. |
The Federal Highway Administration, WSDOT and the City of Seattle are developing a second Supplemental Draft Environmental Impact Statement (SDEIS) for replacing the viaduct between S. King Street and the Battery Street Tunnel. This document will build on previous environmental analysis of cut-and-cover tunnel and elevated structure alternatives and will look at how the transportation system functions, with a focus on the bored tunnel alternative. The SDEIS will be published for public review in fall 2010.
Bored tunnel alternative
This alternative, recommended by the Governor, King County Executive, Seattle Mayor and Port of Seattle CEO in January 2009, would move SR 99 into a bored tunnel beneath downtown, reconnect the street grid at the ends of the tunnel and remove the viaduct along the waterfront.
A major advantage of this proposal is that construction impacts to businesses and the traveling public would be minimized. Using a tunnel boring machine would give us the option of building the new corridor while SR 99 remains open to traffic.
Tunnel route and portals
Value engineering efforts led us to evaluate new north and south portal locations and a number of potential alignments for the proposed SR 99 bored tunnel. The current proposal for the tunnel route begins on Alaskan Way south of S. King Street, then moves toward First Avenue near Yesler Way, turns north near Stewart Street and ends at Sixth Avenue N. and Thomas Street.
We established working groups to help inform the design for the tunnel's north and south connections. Materials presented to the working groups are available online.
Additional bored tunnel information
Program improvements led by the County and City
In January 2009, when the executives recommended replacing the viaduct with the bored tunnel alternative, King County and the City of Seattle envisioned other improvements as part of the viaduct replacement program.
The City would build a new roadway (funded by the State) and new public open space along the waterfront once the viaduct is removed, improve other city streets and replace the central waterfront seawall, and the County would seek new funding sources to invest in expanded transit service. The City and County are responsible for managing these projects, including their environmental review.
The Governor and Mayor signed a memorandum of agreement (pdf 26 kb) in October 2009 that outlines the State and City's responsibilities for the viaduct replacement program.
How did we develop the bored tunnel alternative?
Updated February 2010