Unless there is other legislation that specifically deals with this topic then the SAFECOM act does allow for CFS to "assume control". In the context of an Emergency on a road I would feel very confident to close a road and or direct traffic as required while CFS crews are combatting the emergency.
So far this in this thread we have been discussing road accidents. We would also be justified in closing roads and or directing traffic for fires, HAZMAT or any other incident that requires traffic management. This could be two fold - protecting passers by and CFS crews.
This is my take on it only