(A)   The driver of any motor vehicle carrying passengers for hire, or of any bus, as that term is defined in 47 O.S. § 1-105, owned or operated by a licensed child care facility while carrying children, or of any school bus carrying any schoolchild, or of any vehicle carrying explosive substances or flammable liquids as a cargo or part of a cargo, before crossing at grade any track or tracks of a railroad, shall stop the vehicle within 50 feet but not less than 15 feet from the nearest rail of the railroad and while stopped, shall listen and look in both directions along the track for any approaching train and for signals indicating the approach of a train, except as hereinafter provided, and shall not proceed until he or she can do so safely.  After stopping as required herein and upon proceeding when it is safe to do so, the driver of any vehicle shall cross only in the gear of the vehicle that there will be no necessity for changing gears while traversing the crossing, and the driver shall not shift gears while crossing the track or tracks.
   (B)   No stop need be made at any crossing where a police officer or a traffic-control signal directs traffic to proceed.
(47 O.S. § 11-702)  (`90 Code, § 20-73)