Spokesman Travis Phelps said the framework is in place and workers are tightening bolts and welding sections on the temporary structure that's 24 feet wide and 160 feet long.
He said they'll be installing panels Monday that will be paved with asphalt to form the new bridge deck.
Some other work remains, such as divers' inspecting piers, so the department isn't saying yet what day the Mount Vernon bridge will reopen.
Traffic has been detoured since May 23 when a truck with and oversize load struck the 58-year-old span, causing it to crumble. The bridge carried 71,000 vehicles a day.
More Northwest Headlines
Assaults on staff at state psych hospital costing millions 10:31 a.m. Power restored to all 10 days after Washington windstorm 10:37 a.m. Seattle to pay $100,000 for geography studentís rough arrest Casey Kasemís widow sued for wrongful death DNA links Kelso man to 2000 killing, may clear victimís son EWU to name campus center for Native American activist 2,000 customers still affected by Spokane power outages Washington project ensures forest stores carbon for decades
Our new comment system is not supported in IE 7. Please upgrade your browser here.