..."[T]he following provisions shall apply to the operation of heavy-duty diesel powered motor vehicles:

A. No person shall permit, cause, suffer or allow the engine of a heavy-duty diesel powered motor vehicle to idle prior to, during layover between, or at the conclusion of, any trip or route for any period of time beyond that which is reasonably required to attain, or to secure from, normal operating conditions. The maximum allowable period of idling shall not exceed two (2) consecutive minutes or zero (0) for layovers, except under the following conditions:

1. The engine may be idled for a period of up to five (5) consecutive minutes when the ambient temperature is less than 32°F (0°C).
2. The engine may be idled for a period of up to twenty (20) consecutive minutes when the ambient temperature is less than 20°F (-7°C).
3. The engine may be idled for a period of up to twenty (20) consecutive minutes for buses equipped with air conditioning and non-openable windows and the ambient temperature is equal to or greater than 75°F.

B. No person shall permit, cause, suffer or allow the engine of a heavy-duty diesel powered motor vehicle to be accelerated while idling at any time.

For the purposes of this Section, the term "heavy-duty" shall apply to any motor vehicle with a gross vehicle weight of more than 8500 pounds or with a passenger carrying capacity of more than 12 persons."

"No person shall cause or permit the engine of a bus or truck to idle for longer than five (5) minutes while parking, stopping or standing at any terminal point along an established route, except that this prohibition shall not apply to;

(a) any bus or truck when the ambient temperature is forty degrees Fahrenheit (40°F) or less;

(b) a bus or truck enroute to a destination but stopped by traffic congestion; or

(c) a bus that pursuant to law must maintain a specific temperature for passenger comfort, provided that such a bus may idle in excess of five (5) minutes only to the minimum extent necessary to comply with such law."