The man was driving eastbound on Willow Pass Road in unincorporated Contra Costa County's Bay Point area at about 7:25 a.m. when his Nissan Sentra traveled into the westbound lane and smashed into a school bus just west of Bailey Road, CHP Officer Scott Yox said.
There were no students on the bus and its driver complained of pain but was not seriously injured, according to Yox.
The driver of the Nissan, however, died in the crash and his body was extricated from the mangled car, Yox said.
Authorities are investigating what caused the man to veer into oncoming traffic.
"Fatigue, intoxication, mechanical failure with his vehicle, or even an intentional act, like if he planned to go head-on with a large object," are some possibilities, Yox said.
Willow Pass Road between Bailey Road and Clearland Drive was closed while emergency personnel responded to the crash, Yox said.
