The tunnel proposed to Seattle voters in 2007 was a cut-and-cover tunnel, which would have been constructed by excavating a 60-foot-deep trench along the central waterfront. It would have required closure of the viaduct for several years, causing disruption to traffic and businesses.

The bored tunnel will be located beneath downtown and Belltown and be up to 200 feet below the surface, minimizing impacts on businesses and traffic. Traffic will be able to stay on the viaduct through most of the bored tunnel's construction.