Tunneling Toward a New State Route 99 Corridor

December 10, 2013

In summer 2013, Bertha, the world’s largest-diameter tunneling machine began a historic journey beneath downtown Seattle. Its purpose: dig a tunnel to replace the SR 99 Alaskan Way Viaduct, a double-deck highway that has spanned the downtown waterfront for more than half a century. The machine’s task sounds straightforward enough, but the story behind it is complicated. It begins with an earthquake in 2001 that damaged the viaduct and led to a decade of public debate about how to replace the vulnerable structure. More than 90 alternatives were studied, several votes were held and the story’s conclusion is unfolding now, as the Washington State Department of Transportation builds a new SR 99 corridor through Seattle.

Matthew Preedy, PE (BSCE ’92)
Deputy Program Administrator, Alaskan Way Viaduct Replacement Program
Washington State Department of Transportation