From the Caltrans Facebook page:
Before nightfall crews in Eureka will be placing barricades with flashing beacons at certain intersections along U.S. 101 in Eureka and Route 255 in Arcata to indicate the locations of traffic signals. We expect all our signals to be dark by nightfall. Remember: When traffic signals are dark or flashing red, travelers should treat the intersection as an all-way stop. Then, allow those that stopped before you at the intersection to proceed first.