According to the California Highway Patrol, the man, identified only as a male in his 40s, was stopped on the southbound side of the 5 Freeway, helping a stranded driver.
As he was attempting to load up the vehicle onto his tow truck, he was struck by a Nissan Versa that was passing by.
The woman driving the Nissan, identified as Rachel Fewings, and the driver of the disabled vehicle remained at the scene, both of whom have been fully cooperative with officers, CHP said.
Investigators said alcohol and/or drugs are not suspected to be a factor in the crash.
The cause of the collision remains under investigation.