Price Canyon Road near Edna will close from 7 p.m. to 5 a.m. Monday and Tuesday nights, according to the San Luis Obispo County Department of Public Works.
The closures will take place between Highway 227 and Corral de Piedra Road. Public Works is advising motorists to instead use Highways 101 or 227.
Price Canyon Road has been considered a top priority for widening for the past 10 years, according to Public Works, which said Caltrans has identified the road as a key alternate route for South County traffic.
Public Works said the project will improve driver and bicyclist safety by providing full bike lanes.
It is funded by the federal and county governments.