(a) Whenever any person driving a vehicle approaches a railroad grade crossing under any of the circumstances stated in this section the driver of the vehicle shall stop within fifty feet, but not less than fifteen feet, from the nearest rail of the railroad and shall not proceed until he 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 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 one thousand, five hundred feet of the highway crossing emits a signal audible from such distance and the train, by reason of its speed or nearness to the crossing, is an immediate hazard.

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

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