A 911 call with suspicious circumstances at 7:14 a.m. lead officers to the body, on the shoulder of the highway north of Washington Avenue, Johnson said.
Officials have not determined how much of the accident the caller witnessed, but a vehicle description of the car that hit the man was reported, Johnson said.
Officers are searching for a gray, late model, possibly a General Motors vehicle, Johnson said.
The southbound side of the highway was shut down for about an hour as the coroner responded to the scene, and a Sig-alert was issued at about 7:50 a.m., according to the CHP.
The Nos. 1, 2, and 3 lanes were opened as of about 8:40 a.m., but the No. 4 lane remains closed as the investigation into the accident continues, Johnson said.