The California Department of Transportation said on its Facebook page that a crew was working Thursday along a one-lane highway in Mendocino County, where a retaining wall is being constructed.
A crew member captured the scene on video as a long semitruck tried to navigate the steep curve. While the crew shouted words of warning, the driver lost control, and the truck went over the embankment.
Caltrans said the driver wasn't hurt.
The transit agency says it hopes the incident will remind big rig drivers that no vehicles greater than 39 feet in length are allowed along that stretch of highway.