Traffic on Interstate 5 will be detoured through Mount Vernon this Saturday night, Sept. 14, so crews can move the permanent replacement for the Skagit River bridge into place.
Transportation department officials said traffic will be detoured from 7 p.m. Saturday until about 7 a.m. Sunday. WSDOT offered this caveat, however:
"While the contractor expects the detour to last only 12 hours, it is a complex operation and the closure could be extended several hours."
Moving the new spans into place is not a simple process, but contractor Max J. Kuney Co. thinks they'll have it done in 12 hours.
Once I-5 traffic is detoured, crews will move the two temporary spans out of the way using hydraulic jacks that slide on Teflon pads and long steel rails. Crews will then use a similar system to slide the new 900-ton span into position from the west side of the existing bridge and lower and lock it into place.
The original northernmost span of the bridge collapsed after an overheight truck load hit some crossbeams, causing the steel truss to give way. Crews installed a temporary span in June.
The bridge carries an average 71,000 vehicles a day.
Having the new span in place should allow traffic to resume freeway speed, DOT said. The speed limit near the temporary span has been reduced to 40 mph.
More nighttime detours will begin next Monday, Sept. 16 as girders are retrofitted to improve clearance on the bridge.
Other overnight closures are likely this fall, when workers cut and replace several of the curved overhead crossbeams, raising them to 18 feet to reduce the risk of trucks hitting them.
WSDOT released this time lapse video on YouTube that shows crews building the permanent replacement bridge: