Mississippi Code Title 77. Public Utilities and Carriers § 77-9-223

(a) to tramroads, mill roads and roads engaged principally in lumber or logging transportation in connection with mills;

(b) to railroad systems under thirty miles long which do not run regular night schedules;

(c) to any engine, the lighting equipment of which shall have failed during a trip, provided that it be shown that the equipment was in efficient and effective working condition when the trip was begun; or

(d) to switch engines going to and returning from wrecks, or sent out on a main line to bring into a terminal a train, the engine of which has become disabled.