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

(c) Every motor vehicle used in commerce with a gross vehicle weight rating of greater than ten thousand pounds not subject to the requirements of subdivision (a) of this section: (i) shall upon approaching a railroad grade crossing, be driven at a rate of speed which will permit said motor vehicle to be stopped before reaching the nearest rail of such crossing, and shall not be driven upon or over such crossing until due caution has been taken to ascertain that the course is clear; and (ii) shall stop at such crossing if the course is not clear.

(d) In addition to the requirements of subdivisions (a) and (c) of this section, the driver of a commercial vehicle must check street-railway grade crossings within a business or residence district.

(e) Notwithstanding any other provision of law, every operator of a commercial motor vehicle shall obey a traffic control device or the directions of a police officer at a railroad grade crossing.

(f) Every person convicted of a violation of this section shall for a first conviction thereof be punished by a fine of not more than one hundred fifty dollars or by imprisonment for not more than fifteen days or by both such fine and imprisonment; for a conviction of a second violation, both of which were committed within a period of thirty months, such person shall be punished by a fine of not more than five hundred dollars or by imprisonment for not more than forty-five days or by both such fine and imprisonment; upon a conviction of a third or subsequent violation, all of which were committed within a period of thirty months, such person shall be punished by a fine of not more than seven hundred fifty dollars or by imprisonment for not more than ninety days or by both such fine and imprisonment.