BATH, Maine — The Maine Department of Transportation is replacing the U.S. Route 1 viaduct in Bath, and motorists should plan for disruptions.

Work is getting underway after Columbus Day on the bridge-like structure that has carried U.S. 1 traffic over historic downtown Bath since 1958. The new viaduct will be a quarter-mile long and will run from High Street to the Sagadahoc Bridge on the Kennebec River.

Last April, the viaduct was closed to replace aging guardrails after a sport utility vehicle crashed through one and fell onto a pickup truck below.

But the larger problem is that the structure has reached the end of its lifespan. Officials say the $12 million project is due to be completed by Memorial Day 2017.