"It's a big mystery," Officer Steve Creel said this afternoon.
The man was wearing a black shirt and blue jeans, so it was impossible for drivers to see him on the dark roadway and stop in time, Creel said.
He was hit on southbound Highway 680 just north of Mission Boulevard at about 4 a.m. as he walked near the center divide. He was first struck by a silver Jeep Cherokee and then run over by a Chevy Suburban sport utility vehicle, according to Creel.
The two drivers stopped at the scene and cooperated with the CHP, Creel said. He said there's no indication the drivers were under the influence of drugs or alcohol and they aren't expected to face charges.
Creel said investigators are awaiting a toxicology report that will indicate whether the pedestrian had taken drugs or been drinking.
A spokesman for the Alameda County coroner's bureau said the pedestrian had a California identification card but hasn't yet been positively identified.