N.Y. Comp. Codes R. & Regs. tit. 21, § 100.10 – Saddle-mounted vehicles.

(a) the wheels of no more than one axle or set of tandem axles of each transported vehicle is on the roadway during the course of transportation;
(b) no such transported vehicle furnishes any motive power; and
(c) each such transported vehicle is mounted upon a device designed and constructed so as to be readily dismountable and which performs the function of a conventional fifth wheel.

In an operation in which not more than two motor vehicles constitute the commodity being transported, the combination of one such transported vehicle and the transporting vehicle, and two such transported vehicles and the transporting vehicle, shall be considered a single and double saddle-mount respectively; provided, however, that: