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​After three years and millions of dollars in repairs, the SR99 tunneling machine in Seattle has resumed operations.​

​After three years and millions of dollars in repairs, the SR99 tunneling machine in Seattle has resumed operations.​

How does one build a highway inside a giant tunnel?

How does one build a highway inside a giant tunnel?

Gizmag goes inside the world's largest tunnel boring machine By David Szondy July 22, 2013 Map of the SR 99 tunnel (Image: WSDOT)

Gizmag goes inside the world's largest tunnel boring machine By David Szondy July 22, 2013 Map of the SR 99 tunnel (Image: WSDOT)

VIDEO: Why the Highway 99 tunneling machine 'is a submarine'

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