Contents tagged with sr99
Agreement was reached after an intensive public outreach effort. A 29-memeber Stakeholder Advisory Committee, which provided feedback on replacement options, met 16 times, and a majority asked that a bored tunnel replacement be considered further. Ten public meetings and more than 85 community briefings were also held. Comments from the public covered a range of topics, focusing on preserving capacity for the future and opening up Seattle's waterfront.
Moving SR 99 traffic underground will have several environmental benefits. New stormwater treatment will improve water quality in Elliott Bay, and traffic noise will be contained within the tunnel. New open space and public access will also be created on the waterfront once the viaduct is removed.
The viaduct section of SR 99 is a main north-south route through Seattle, carrying more than 100,000 vehicles per day. Many commuters and industries, particularly the Port of Seattle, depend on this vital corridor as an alternative to I-5, since the stretch of I-5 through downtown Seattle is the most congested section of freeway in the state. Replacing the viaduct with a tunnel will ensure this capacity is available as the region grows. City street improvements and transit investments will also help accommodate future growth.
A major advantage of this bored tunnel is that it minimizes construction disruptions for businesses and the traveling public. It allows us to build the rest of the new SR 99 corridor while the remaining viaduct stays open to traffic. The SR 99 closures required during construction of a cut-and-cover tunnel or new viaduct would have required longer trips on detour routes through downtown Seattle for three to four years.
New transit service is an essential part of the Alaskan Way Viaduct replacement, because it would provide a reliable and efficient way for Seattle residents to get to and from downtown. Without added transit service, drivers would have a more difficult time reaching the tunnel, because city streets would likely be more congested. This would become more important as the city and region continue to grow.
Most freight will be able to use the SR 99 tunnel. Vehicles hauling hazardous or combustible materials will be prohibited from the tunnel, similar to current restrictions in the Battery Street Tunnel and on the viaduct during peak hours. These vehicles will take I-5 or the waterfront, as they do today.
The SR 99 tunnel will maintain freight routes through Seattle and preserve I-5 for regional and state freight trips. It will also provide a route through the city for vehicles that would otherwise use city streets.
Some freight trips destined for Ballard and the Interbay industrial area will likely use the new Alaskan Way street along the waterfront, with its crossing over the railroad tracks to Elliott and Western avenues. Traffic signals along the waterfront will be operated to ensure through trips move efficiently.
Freight trips leaving Port of Seattle terminals will also have improved access to I-5 and I-90 as a result of SR 519 and Spokane Street improvements and a new overpass at South Atlantic Street, which is included in our south-end viaduct replacement project.
Drivers heading north on SR 99 will have access to downtown Seattle via an off-ramp to a new Alaskan Way street. The new Alaskan Way will provide several east-west connections to downtown. This access will replace the function of today’s single midtown viaduct off-ramp. Depending on the destination, some trips will get shorter while others may take a few minutes longer.
West Seattle residents can also reach downtown using the new Spokane Street Viaduct off-ramp to Fourth Avenue South.
Residents from northwest Seattle will have two options to get to or through downtown Seattle. They could travel along Elliott Avenue, as they do today, and drive down a new bridge over the railroad tracks near Pike Place Market to a new Alaskan Way street along the waterfront. Alaskan Way will connect directly to SR 99 near South Royal Brougham Way.
If northwest Seattle residents want to use the SR 99 tunnel, they could take the new two-way Mercer Street to Sixth Avenue North and enter the tunnel at Republican Street. They could also use any of the existing connections to Aurora Avenue north of Mercer Street.
We signed a design-build contract with Seattle Tunnel Partners in January 2011. Design-build combines project design and construction in a single contract.
More than 90 percent of the design-build work will be performed for a fixed price. The remaining amount includes work such as grouting to control ground settlement, building repairs along the tunnel route, unplanned repairs to the boring machine and work stoppages due to differing site conditions. For these items, we established risk sharing with the design-builder.
We have set aside $205 million for known and unknown risks during tunnel construction. This amounts to 15 percent of the design-build contract, which is on the high end of industry standards.
There are a number of successful tunnel projects with sizes similar to the SR 99 tunnel, which is being designed with an exterior diameter of 57.5 feet and length of 1.7 miles. Examples include:
- China' Shanghai Yangtze River Tunnel: Includes two bores, each about 5 miles long with a 50.6-foot diameter.
- Germany's Fourth Elbe River Tunnel: Includes a single bore with a length of about 2 miles and a 46.6 foot diameter.
- Spain's Madrid M30: Includes bores with a length of about 5 miles and a 49.5-foot diameter.
Tunnel boring machines have been developing at a rapid rate with a major increase in diameter, better ground control, and improved reliability. These machines can now safely and efficiently excavate almost and type of soil, rock or groundwater conditions.