(a) Whenever any person driving a vehicle approaches a railroad grade crossing under any of the circumstances stated in this section, the driver of such vehicle shall stop within 50 feet but not less than 15 feet from the nearest rail of such railroad, and shall not proceed until such driver can do so safely. The foregoing requirements shall apply when:

(1) A clearly visible electric or mechanical signal device gives warning of the immediate approach of a railroad train or other on-track equipment;

(2) a crossing gate is lowered or when a human flagman 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 1,500 feet of the highway crossing emits a signal audible from such distance and such railroad train or other on-track equipment, by reason of its speed or nearness to such 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 such crossing.

(b) No person shall drive any vehicle through, around or under any crossing gate or barrier at a railroad crossing while such gate or barrier is closed or is being opened or closed.