CHP says Officer Andrew Camilleri and another officer were parked in their patrol vehicle on the shoulder of Interstate 880 in Hayward when another auto struck the rear of the patrol auto at approximately 11:30 p.m. on Christmas Eve. He is now being treated at Eden Medical Center.
The other officer, Jonathan Velasquez, was treated at a hospital and released.
Officers responded shortly before midnight to reports of a collision in the southbound lanes of Interstate-880 just north of Highway 92 involving a red auto and a CHP vehicle, Bay Area television station KPIX reported.
The 33-year-old officer had been with the CHP for a little over a year. Sanchez, who declined to release the driver's name, said the driver may also have been under the influence of marijuana.
"The impact was so severe that it turned a utility vehicle into a compact vehicle", a CHP official said at a Christmas morning news conference. Camilleri leaves behind a wife and three young children.
Walcott said the second officer suffered minor injuries.
Sanchez said the suspected intoxicated driver was coming home from a party and "obviously had too much to drink and too much to smoke" when the collision happened, the East Bay Times reports. "Today is a tragic day".
Gov. Jerry Brown said Camilleri died while "working to keep our communities safe".
Flags at the Capitol will be flown at half-staff in the fallen officer's honor.
"We join his family, companions and the whole California Highway Patrol in grieving his passing and in regarding his forfeit", the announcement read.
A driver drifted off the road from the freeway and hit the right rear part of the CHP cruiser.