(a) The idling restrictions set forth in section two of this article do not apply to motor homes, commercial implements of husbandry, implements of husbandry or farm tractors.
(b) The idling restrictions set forth in section two of this article do not apply to construction equipment that cannot be licensed for on-road driving or construction equipment that is not designed primarily for on-road driving, notwithstanding that such equipment may be operated or driven on road from time to time and in the course of performing its primary functions: Provided, That idling is necessary to power work-related mechanical, safety or electrical operations related to construction operations other than propulsion.
(c) A diesel-powered motor vehicle with a gross weight of ten thousand one pounds or more may idle beyond the time allowed in subsection (a) for one or more of the following reasons:
(1) When a vehicle idles while forced to remain motionless because of on-highway traffic, an official traffic control device or signal or at the direction of a law-enforcement official.