The design problem occurred along State Route 16, Washington Department of Transportation Secretary Paula Hammond told The News Tribune of Tacoma.

"This obviously is something we have not done right. And it is something we are going to fix," Hammond said Monday.

The agency intends to use money from the project's contingency fund to rebuild the ramp.

Hammond said her staff could have done a better job of communicating about the Nalley Valley Viaduct project.

The agency caught the mistake last winter when the off-ramp from the eastbound highway was nearly 90 percent completed. Work began Friday to tear up the pavement, calling public attention to the problem.

The fix won't delay completion of the westbound portion of the project slated for the fall of 2011, officials said.

Project staff previously said the project was proceeding smoothly with no major problems. Hammond made no mention of the problem when she met with the newspaper June 3 to talk about the project, the News Tribune reported.

Officials said two design teams were working on the project.

The team working on the eastbound lanes added a third lane of traffic, but the other team doing the westbound lanes was unaware of the change, officials said.

In addition, engineers were transferred to a different project.

"The result is we weren't doing the check, check and double-checks." Hammond said.

Regional administrator Kevin Dayton said the department created an independent construction office to review project contracts after the design mistake was uncovered. He also plans monthly meetings with his project teams.

Read more about the mistake here.