Cal. Code Regs. tit. 13 § 1214
No driver shall operate a motor vehicle, and a motor carrier shall not require or permit a driver to operate a motor vehicle, while the driver's ability or alertness is so impaired, or so likely to become impaired, through fatigue, illness, or any other cause, as to make it unsafe for him/her to begin or continue to operate the motor vehicle. However, in a case of grave emergency where the hazard to occupants of the motor vehicle or other users of the highway would be increased by compliance with this section, the driver may continue to operate the motor vehicle to the nearest place at which that hazard is removed.
Cal. Code Regs. Tit. 13, § 1214
Note: Authority cited: Sections 31401, 34500.1, 34501, 34501.5 and 34508, Vehicle Code; and Section 39831, Education Code. Reference: Sections 545, 31401, 34501, 34501.5 and 34508, Vehicle Code; and Section 39831, Education Code.