(a) An operator transporting migrant agricultural workers who approaches a railroad grade crossing:
(1) shall stop the motor vehicle not less than 15 feet or more than 50 feet from the nearest rail of the crossing; and
(2) may proceed only after the operator determines that the course is clear.
(b) An operator is not required to stop at:
(1) a streetcar crossing that is in a municipal business or residential district;
(2) a railroad grade crossing at which a police officer or traffic-control signal other than a railroad flashing signal directs traffic to proceed; or
(3) a grade crossing that the proper state authority has clearly marked as being abandoned or exempted if the marking can be read from the operator's position.
(c) The motor vehicle must display a sign on the rear of the vehicle that states: "This Vehicle Stops at Railroad Crossings."