A 51-year-old Antioch man was driving a pickup truck east on Highway 4 west of Somersville Road when he struck Sears, who was walking in the No. 2 lane, California Highway Patrol Officer Tom Maguire said.
The driver, who initially thought he had hit some debris, immediately pulled off the highway and called the CHP to report the incident.
Investigators believe Sears may have been under the influence of alcohol.
It is possible that he was hit by more than one vehicle, and investigators are still searching for other drivers who may have been involved.
The road was closed for nearly two hours while officers investigated.
Anyone with information about the case is asked to call the CHP office in Martinez at (925) 646-4980.