California Code, Vehicle Code - VEH § 32104

(a) It is unlawful for the motor carrier or its authorized agent to drive or to permit the driving of any vehicle transporting inhalation hazards, or for the driver to drive the vehicle, upon any public highway not designated in regulations adopted by the department as a route for the transportation of inhalation hazards.  This subdivision shall not apply when the use of the highway is required (1) to permit delivery of, or the loading of, inhalation hazards at a point not on a highway designated as a route for the transportation of inhalation hazards, or (2) to permit the vehicle to proceed to, and return from, an inspection stop, safe stopping place, or safe parking place.

(b) It is unlawful for the driver of any vehicle transporting inhalation hazards to stop at any place other than a safe stopping place, safe parking place, or an inspection stop unless the vehicle is disabled or except when necessary to avoid conflict with other traffic or to comply with the orders of a peace officer or an official traffic control device.

(c) This section shall become operative on January 1, 1992.