Veh. Code, § 31617

In the event of an emergency, the Department of the California Highway Patrol is authorized to suspend or change any designated route for the transportation of explosives or to temporarily designate new or additional routes for such transportation. The Department of the California Highway Patrol shall, unless the nature of the emergency makes it impracticable to do so, consult with local fire officials in the area or areas affected before making any such changes or new designations. If the changes or new designations are made before they can be discussed with those officials, the Department of the California Highway Patrol shall immediately notify the appropriate officials of his action.

The change in or new designation of routes shall not be effective for more than 90 days from the date of such action, unless the Department of the California Highway Patrol determines that the change or new designation should become permanent, in which case the Department of the California Highway Patrol shall, within the 90-day period, initiate action to make the change or new designation permanent in accordance with the provisions of Section 31616 and in which case the emergency change or designation shall remain in effect until superseded by a regulation of the Department of the California Highway Patrol.