(1) The driver of any private carrier bus, carrying any passenger, before crossing at grade any track or tracks of a railroad, must stop such vehicle within fifty feet but no less than fifteen feet from the nearest rail of such railroad and while so stopped must listen and look in both directions along such track for any approaching train, and for signals indicating the approach of a train and must not proceed until he can do so safely.

(2) After stopping as required and upon proceeding when it is safe to do so the driver of any private carrier bus must cross only in such gear of the vehicle that there will be no necessity for changing gears while traversing such crossing and the driver must not shift gears while crossing the track or tracks.

(3) No stop need be made at any such crossing where a police officer or a traffic-control signal directs traffic to proceed.