Cal. Veh. Code § 35650

The Department of Transportation, whenever it determines after an engineering investigation that any highway under its jurisdiction will with safety to itself sustain vehicles and loads weighing more than the maximum weight limits set forth in this code, shall have authority to declare and to fix a weight limit for the highway greater than the maximum weight limit set forth in this code. Thereafter it shall be lawful to operate or move vehicles and loads of a gross weight upon the highways designated, equal to but not in excess of the maximum weight limit fixed by the department.