As used in this article the term “motor vehicle” shall include trailers and all vehicles included in the definition of the term “motor vehicle” contained in section one hundred twenty-five of this chapter except the following:

1. Road rollers, tractor cranes, truck cranes, power shovels, road building machines, snow plows, road sweepers, sand spreaders, well drillers, well servicing rigs, feed processing machines, mobile car crushers, earth movers, trucks with small wheels used in a factory, warehouse or railroad station, agricultural spreaders and sprayers, or a tractor-trailer combination designed and used exclusively for the same purpose as a vehicle specifically included in the foregoing, or

2. Vehicles inspected by or operating under a certificate of inspection authorized by the commissioner of transportation or the interstate commerce commission, or of a municipally owned and operated transit system, or

3. Farm vehicles registered under subdivision thirteen of section four hundred one of this chapter, self-propelled combines, self-propelled corn and hay harvesting machines and tractors used exclusively for agricultural purposes, or

4. Vehicles subject to inspection and licensing by local authorities provided such inspection by such local authorities conforms with the standards established by the commissioner under this article, or

5. Fire vehicles, except ambulances; or

6. Police vehicles for which the department operating such vehicles has submitted a plan approved by the commissioner, who shall establish the standards therefor, for periodic inspection thereof. Such plans shall be submitted to the commissioner by September thirtieth of each year. In determining the acceptability of such inspection plans and in establishing standards therefor, the commissioner shall require that such periodic inspections shall be substantially equivalent to inspections required for other motor vehicles under this article and shall be made with respect to such mechanisms and equipment as shall be determined by the commissioner to be necessary for the proper and safe operation of such vehicles.