While the Lewis and Clark River Bridge in Astoria is closed until Aug. 1, the nearby Old Youngs Bay Bridge on Alternate Highway 101 will undergo repairs to its electrical and mechanical systems from the 1920s.

Starting Monday, Oregon Bridge Construction of Stayton, the contractor on the project, will begin work on the Old Youngs Bay Bridge electrical system.

The construction work is part of a three-year, $16 million rehabilitation project to repair both bridges, according to the Oregon Department of Transportation.

Travelers should plan for intermittent lane closures on the Old Youngs Bay Bridge over the next three years. The entire project is expected to be completed in November 2017.

Despite the closures, access to local businesses near the bridges will remain open during all phases of construction. Most of the work will be done during the daytime with flaggers controlling a single-lane of traffic, ODOT said, and only minor delays are expected during construction activities and travelers should drive through the area with caution.

“The bottom line is that there will be short/minor delays of no more than five minutes or so during construction activities, and access to all businesses around the bridge will be maintained,” ODOT spokesman Lou Torres said.

U.S. Highway 101 is the main detour route. Travelers coming from Seaside or local motorists in the area can use Fort Clatsop Road to Lewis and Clark Road as a detour route to access local businesses near the bridge.

The electrical and mechanical systems on the Old Youngs Bay Bridge are considered long past their useful life and need to be upgraded to meet operational and safety needs for marine and highway use, according to ODOT.

Both bridges are nearly a century old.

The Lewis and Clark River Bridge — the last remaining single leaf bascule drawspan in Oregon — was built in 1924. The Old Youngs Bay Bridge, built in 1921, is one of four remaining double-leaf bascule bridges in Oregon.

ODOT describes a bascule style bridge as a draw bridge that uses a counterweight to balance the span or “leaf” throughout the entire upswing, providing clearance for boat traffic.

As of 2013, the average traffic count on Old Youngs Bay Bridge was 20,000 vehicles per day. Lewis and Clark River Bridge had an average of 11,400 travelers per day.

The restoration work is expected to add decades to the lifespan of the bridges, Torres said.