Twelve hours. That is all Max J. Kuney Co. crews expect to need to slide over the new, permanent Interstate 5 span over the Skagit River, replacing the temporary bridge in place since June after I-5 collapsed in May.

The slide-over will happen Saturday, Sept. 14, and includes the removal of the temporary span. The finishing touches needed this week to the permanent bridge sitting just feet to the west of the final resting place? The curing of the concrete deck.

The Washington State Dept. of Transportation plans to close I-5 starting at 7 p.m. on Saturday, detouring traffic around the interstate, and starting a 12-hour window of removing the temporary span and locking in the permanent one. Using hydraulic jacks, Teflon pads and steel rails, the new 900-ton span will slide from the west, lower slightly and lock into place, hopefully reopening I-5 by 7 a.m. on Sunday.

You can see the entire bridge-making process for the Skagit River span in this visualization video.

The fast-paced project started taking shape this June. An oversize load hit the bridge in May, collapsing an entire four-lane, 1,111-ft span into the river below. Crews had a temporary bridge in place by mid-June and then started working on a permanent fix. All along, the state planned to have the permanent span in place sometime in September, so moving the final bridge into place on Sept. 14 marks a quick completion of the roughly $15 million project.

The project hit a major milestone in mid-August when crews finished setting the eight girders that make up the bridge, which can be seen in this cool WSDOT time-lapse video.

But work won’t stop on the bridge once the northernmost section gets replaced. Starting on Monday, Sept. 16, the other three bridge spans — all sections are of equal length — will start to receive a retrofit, which replaces the curved support girders with completely horizontal supports for a taller vertical clearance from the roadway.

While Jay Drye, WSDOT’s assistant regional administrator, says that “moving bridges is not easy,” crews hope to make it look so on Saturday.

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for TIMEPopular MechanicsSports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.