Editing 4-2-0 (section)

===South Africa===
[[File:Dutton's Road-Rail Tractor no. RR973.jpg|thumb|left|[[South African Dutton road-rail tractors|Dutton road-rail tractor]], a modified Yorkshire steam tractor, c. 1924]]
In 1923, the South African Railways conducted trials with a prototype petrol-paraffin powered road-rail tractor and, in 1924, placed at least two [[South African Dutton road-rail tractors|Dutton steam road-rail tractors]] in service on the new {{Track gauge|2ft|allk=on}} narrow gauge line between [[Naboomspruit]] and Singlewood in Transvaal. The petrol-paraffin prototype and one of the latter had a {{nowrap|4-2-0}} wheel arrangement.<ref name="SAR&H Oct 1945">Espitalier, T.J.; Day, W.A.J. (1945). ''The Locomotive in South Africa - A Brief History of Railway Development. Chapter VII - South African Railways (Continued).'' South African Railways and Harbours Magazine, October 1945. pp. 782-783.</ref><ref name="Paxton-Bourne">{{Paxton-Bourne|pages=118–119}}</ref>

The prototype was a modified [[Dennis Specialist Vehicles|Dennis tractor]] which was fitted with a removable bogie between the front wheels to lift them high enough to prevent ground contact. A ball pin on the bogie fit into a socket in the front axle, and the bogie could easily be removed or replaced by running the tractor up a pair of ramps, placed on both sides of the track.<ref name="SAR&H Oct 1945"/><ref name="DaveMills">[http://dave-mills.yolasite.com/stronach-dutton-road-rail.php Stronach-Dutton Road-Rail - The Roadrail System of Traction]</ref><ref name="ComMotor1">''Transport Problems in South Africa - The Dutton Loco-Tractor Advocated as a Solution.'' Article in ''The Commercial Motor'', 24 August 1920. p. 14.</ref><ref name="ComMotor2">[http://archive.commercialmotor.com/article/26th-september-1922/16/important-developme-roadrail-transport ''Important Development Roadrail Transport''. Article in Commercial Motor, 26 September 1922. pp. 168-169.]</ref>

The production model was a modified Yorkshire steam tractor, fitted with jacks at the front to allow a separate bogie to be manoeuvred into position underneath the front axle to guide it on the rails. Without the bogie, the vehicle could still be driven on ordinary roads and had the advantage of being able to be detached and run around the train, without requiring special loops for that purpose. For reversing on the track, as when shunting, the rear wheels were modified to be steerable.<ref name="Paxton-Bourne"/><ref name="DuttonPatent1">[https://patents.google.com/patent/US1306051 Patent: Dutton Light Railway System and Locomotive Therefor, US 1306051 A, Jun 10, 1919]</ref>