Someone else can probably explain it more precisely, but the tunnel in question is needed to replace the Alaskan Way Viaduct, a multi-deck elevated highway that took some damage in an earthquake over a decade ago.  Some authorities have expressed concern that another earthquake of equal or greater magnitude might cause the viaduct to fail like the 1989 Embarcadero collapse in San Francisco, with the potential for significant loss of life.<p>So the decision was made to tear down the viaduct and replace it.  Why not reinforce it or even rebuild it in place with modern construction standards?  Because the viaduct has another drawback besides its seismic vulnerabilities: it&#x27;s big and ugly.  Its removal would enhance property values along the Seattle waterfront tremendously.  Reportedly, the developers who own the affected property are major contributors to the Seattle politicians who have the authority to make the final decision, so fixing the current viaduct was ruled out from the start.  It was only a question of which less-effective solution would be adopted.<p>With a rebuild off the table, the remaining options included surface-only streets, with fewer lanes and more traffic lights; a cut-and-cover tunnel, which would completely disrupt traffic in the area during construction; and the solution that was eventually chosen, a deep tunnel through unstable and poorly-characterized soils that would have to be bored underneath major downtown buildings and thoroughfares.  The tunnel would have about half of the viaduct&#x27;s lane capacity, no room for future expansion, and no downtown exits at all, but it wouldn&#x27;t threaten the all-important view of Puget Sound, and parts of the old viaduct route could remain in use during construction.<p>In other words, it was one of those politically-expedient solutions where lots of other peoples&#x27; money would be spent in the process of making very few people happy.  Schadenfreude was the <i>best-case</i> outcome, since complaining about traffic is as popular around here as football in Texas or religion in Oklahoma.  But we&#x27;re now looking at one of the worst cases: the engineering behind the tunnel (and&#x2F;or the $90 million custom machine that drills it) is proving to be inadequate to the job, so essentially no progress toward replacing the viaduct is being made at all.  Drivers are fuming, lawyers are salivating, mild-mannered newspaper columnists are discovering their inner muckrakers... and seismologists are frowning and muttering ominously.