It is happening on 99 between Ashlan and Grantland in both directions.
Caltrans is installing a concrete safety barrier as it prepares to widen the freeway from four-lanes to six.
Drivers should expect delays starting at 7 p.m. Sunday until 5 a.m. on Friday.
More work will begin again Sunday night.
Traffic in both directions will be reduced to one-lane to install the concrete railing in the median.
