A
typical semi-tractor would be a 2-4-0.
The "steers" axle is not powered, and there are 2 axles of "drivers". The trailer is not part of the "locomotive", so the trailer axles are not counted. Think about a semi puilling 2 or 3 or more trailers - the trailers are more or less "freight cars" and are not part of the locomotive. Furthermore, sometimes semi tractors travel "bobtail" (no trailer at all), so the trailers axles are more or less optional.
Edited 1 time(s). Last edit at 11/14/2017 02:33PM by Rader Sidetrack.