In video taken by another person who happened to be traveling the same way, the man appears to be hanging onto the metal rods on the back of the moving semi-truck.
There are more questions than answers about the incident, including who the man is and what led up that moment.
The person who took the video called the California Highway Patrol and says officers told her they were working on it.
MORE | Video shows man hanging out driver's window on 15 Freeway in Corona
Video shows man hanging out driver's window on 15 Freeway in Corona