Tennessee Code Title 55. Motor and Other Vehicles § 55-8-145

(1) A clearly visible electric or mechanical signal device gives warning of the immediate approach of a railroad train or other on-track equipment, which shall mean any self-propelled machinery or vehicle traveling on a railroad track;

(2) A crossing gate is lowered or when a human flagger gives or continues to give a signal of the approach or passage of a railroad train or other on-track equipment;

(3) A railroad train or other on-track equipment approaching within approximately one thousand five hundred feet (1,500′) of the highway crossing emits a signal audible from such distance and the railroad train or other on-track equipment, by reason of its speed or nearness to the crossing, is an immediate hazard; or

(4) An approaching railroad train or other on-track equipment is plainly visible and is in hazardous proximity to the crossing.