Gov. Jay Inslee announced the reopening Tuesday after inspecting the work and praising workers at Mount Vernon.
The Transportation Department says traffic will be reduced to 40 miles per hour on the narrow temporary span. At 24-feet wide, the 160-foot temporary section is narrower than the old bridge and traffic will have to slow from freeway speed.
Crews have finished nearly all the construction, preparing the deck for asphalt paving and highway striping.
The governor had earlier set a goal of reopening the bridge by mid-June, less than a month since the accident.
Staying on I-5 should be a relief to drivers who have lined up to detour through Mount Vernon and Burlington on the main highway for trade and tourism between Seattle and Vancouver, British Columbia. The section of the freeway is used by 71,000 vehicles a day.
The temporary bridge pieces were supplied by Acrow Bridge through an emergency contract the Transportation Department signed with Atkinson Construction. New Jersey-based Acrow Bridge opened an office in Camas and a warehouse in Washougal this spring so it could more quickly respond to customers in Oregon, Washington, Idaho and other states in the West.
The temporary span and a permanent replacement due this fall will cost nearly $18 million. The federal Transportation Department is paying for all but about $1 million of the work.
The 58-year-old bridge is being restored not replaced. It will still be rated as "functionally obsolete" because it was not designed to handle today's traffic volume and big trucks. It's also "Fracture critical," meaning that if a single, vital component is compromised, the bridge can crumple again.
The driver of the oversize truck felt crowded by another southbound semi-truck on the bridge and the load struck a girder, setting off a structural failure that caused one section of the bridge to fall, a preliminary National Transportation Safety Board report said. A final NTSB report on the cause of the bridge failure is likely months away.
A car and pickup truck went into the water and three people were rescued.
Washington State Patrol Trooper Sean O'Connell was killed May 31 when his motorcycle collided with a truck while he was directing detoured traffic in Conway.