Section 77-9-231 shall not apply:
to railroads whose principal business is hauling logs;
to locomotive engines running for coal or water, doubling hills, returning from trains when broken into, or going to or returning from trains in the yard limits of terminal stations;
to engines engaged in regular switching service in yards or road engines switching at intermediate stations; or
to any locomotive engines in cases of washouts, wrecks, or when going to the assistance of engines so disabled as to block the main track of a railroad.