Speed limits are about to drop temporarily on State Route 107 near the Chehalis River Bridge just south of Montesano.

The Washington Department of Transportation will lower the speed limit from 40 mph to 25 mph for a project to replace timber rails on the south approach with safety rails and to repaint the 58-year-old structure.

The speed limit will drop the week of April 29. Construction is expected to begin as early as May 6 and be done by fall 2020.

The lowered speed limit is enforceable when the signs are posted.

Drivers can expect occasional night and weekend lane closures as crews work to keep the bridge open to local traffic.

“The bridge will remain open during construction (one-way alternating with a signal) to all motorists including legal-loaded semis,” a WSDOT spokeswoman said in an email. “Oversized and overweight vehicles may need to use an alternate route.”

The WSDOT website says, “traffic impacts will be intermittent initially. The long-term traffic impacts (one single lane alternating traffic) are currently scheduled to start in mid-June.”