Photo from WSDOT's Flickr Page
The new Nalley Valley Viaduct had been progressing very well up until an unfortunate mistake was discovered. The Tacoma News Tribune has the story on this error during the construction of the new Nalley Valley Viaduct.
As the project was refined from two lanes to three on the eastbound mainline, engineers needed to move the offramp to make room for the extra lane. But that wasn’t communicated between members of the eastbound design team and the westbound design team. As a result, the engineering plan went out with the offramp in the wrong place.
Luckily the problem was caught before things got worse and at least nothing was structurally deficient. The overall schedule shouldn't be affected and the cost to fix the problem fits within the contingency budget for the project.