Seattle Tube Blog

Proposed Routes:

Click on map below to see larger version:

Possible location of the TUBE - Showing southbound lanes under 6th Avenue, and northbound lanes under 7th Avenue.

Possible use of the existing Battery Street Tunnel as an southbound entrance and northbound exit to service Ballard traffic.

One of several options for the south TUBE junction showing north and south bound access ramps onto Airport Way.

One of several locations for a "generic" elevated roadway over south South Seattle industrial areas.


What is tunnel boring?

Modern day tunnel boring is the process of using large machines to drill holes in the earth. Currently, Sound Transit is using a TBM (Tunnel Boring Machine) to bore two holes almost a mile through Beacon Hill. The Mitsubishi TBM used for the Sound Transit light rail tunnels is 21 feet in diameter. Mitsubishi makes these machines up to 50 feet in diameter for boring three-lane roadways around the world.

Tunnel boring construction for Sound Transit Light Rail under Beacon Hill. The construction zone barely takes up a city block while the majority of the work continues under ground.

Why is this a better idea?

Building a new tunnel route under Seattle will have the least impact on everyone's lives. Just like the Sound Transit light rail tunnel, all the work is being done underground. There would only be a relatively small construction zone at each end of the Seattle TUBE compared to what would be needed to build either a new viaduct or waterfront tunnel.

Where will the south entrances be?

One logical place to put a south entrance for the TUBE is at the lightly traveled end of South Sixth Avenue just east of Quest Stadium. Built below grade, the TUBE could start just under the new I-90 access ramps.

Looking north from the intersection of Holgate and the lightly traveled industrial end of South 6th Ave. There could be plenty of room for TUBE construction here as it is out of the way of Seattle's heavy traffic zones.

Where will the north entrance be?

The north entrance would logically be in the same location as the current north entrance to the Battery Street Tunnel. Due to the wide easements of 6th avenue and the Denny intersection, there is ample room for a new tunnel entrance and egress here.

Looking south at the present entrance of the Battery Street Tunnel on SR99. The TUBE can be built below 6th avenue and use the same entrance.

What about Ballard?

The existing Battery Street Tunnel could be re-purposed to provide easy access from Western Avenue to and from the TUBE. - Giving Ballard commuters efficient access to South Seattle.

What about the Bus Tunnel?

The TUBE would be bored deep below the bus tunnel and would have no impact on Seattle's transit systems.

What about other obstructions?

The north and south routes of the TUBE could be bored down below the 5th, 6th or 7th avenue easements to avoid the deep foundations of Seattle Skyscrapers.

How much will it cost?

Or course it won't come cheap. However, tunnel boring may be more predictable since it is a common construction process used throughout the world. Since this new route would be under the city and over Seattle's industrial areas, it won't be necessary to invest in aesthetics. After the TUBE is in operation, some of Seattle's prime waterfront can be sold to developers to offset the cost of the tunnel's construction. This could reduce the cost of the TUBE by hundreds of millions.

How long will it take?

It's likely to take just as long to build the Seattle TUBE as any version of the viaduct or waterfront tunnel. However, construction could occur most of the time without impacting Seattle traffic.

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