The New Zealand TR class locomotive^{[nb 1]} is a type of diesel shunting locomotives built by many different manufacturers. Defined as "shunting tractors" or "rail tractors"^[1] by KiwiRail and its predecessors,^[2] they are classified "TR" for tractor as a result.^[3] Many of these locomotives have been withdrawn, but some are still in service. The first locomotive of this class was built by NZR in 1924. The most powerful were Japanese-built Hitachi TRs, with 138 kW Cummins engines.^[4]

The typical role of a TR was at small stations where a normal shunting locomotive was not needed due to light traffic. NZR's operating rules allowed TRs to be driven by staff who were not members of the locomotive branch, saving on wages. Other roles have included shunting at railway workshops and depots, and most of the remaining locomotives can still be found at these locations. There are very few stations where they are still in use owing to rationalisations of freight terminals, the trend towards containerisation of traffic, and roving shunting services. A number of locomotives have been leased to industrial operators for private siding use.^[5]

The last TR was built in 1978, TR 191. The greatly reduced needs of NZR and its successors for this type of locomotive, and industrial requirements being able to be handled by other ex-NZR classes or locomotives obtained from elsewhere has meant no TRs have been added since then. However, four locomotives have been reclassified from other types.

The TR classification has been applied to two former industrial locomotives. One of these is TR 81, which was purchased from the Ohai Railway Board in 1955. Built by the Drewry Car Co in the 1930s, it is similar to the first generation 0-4-0 Drewry TRs but was originally fitted with the Gardner 6LW diesel engine. The other is A&G Price no. 222 which was acquired from Pacific Metal Industries in the early 2000s. It was built in 1968 with a 307 hp (229 kW) diesel engine and is of the 0-6-0 wheel arrangement. Originally reclassified DSA 222 it now carries the number TR 1026 and is leased for industrial use.

In the 1990s, EB 26 at Napier was reclassified as TR 1003 and used in the area for shunting work. The EB class were formerly workshops shunting locomotives. The Plains Vintage Railway & Historical Museum of Ashburton, a heritage railway, also reclassified two former industrial locomotives as T^R. Although A & G Price built similar locomotives for NZR, plus a J & F Howard's former Public Works Department shunter no. 976. These locomotives were never owned by New Zealand Railways Department or their successors and thus their T^R classification and numbers are historically fictitious.

On 16 March 2022 KiwiRail announced the retiring of its oldest locomotive dating from 1936, an 85-year old diesel shunt locomotive TR56, which had been based at the Hutt Workshops since the late 1960s. TR56 was gifted to the Rail Heritage Trust for use on the Silver Stream Railway. The replacement is battery-powered and zero-emission; one of 14 300-tonne and 2 110-tonne battery-powered shunt engines purchased.^[6]

All TRs were introduced in the Midland Red livery, except the 6 Hitachi built locomotives. In the 1970s all of them had black and yellow chevron safety stripes painted on their headstocks. In the 1980s all of them were repainted into the "International Orange" livery (orange hoods, yellow ends and grey on the cab). TRs 603 and 920 were repainted in Flying Tomato (long and short hoods and cab red and yellow at each end); six were repainted into the Cato Blue (blue body, grey cab and yellow ends) including 943 that received a "one off" being repainted with a blue short and long hoods, blue at each end and grey on the roof of the cab and on top of the hoods; T^R 109 was repainted with black and yellow "Chevron Safety Stripes" on the headstocks and along the running boards with yellow that cover most of the long hood with red covering the top quarter; TR 626 was repainted white with yellow headstocks and has the "New Zealand Rail" logo on the front and 718 was also repainted white but this time with red headstocks for the Westland Dairy Company.^[13] TRs 56 and 92 were repainted fully yellow with white numbers on each side of their cabs. In 1994 TR 943 was repainted at Hillside Workshops and was repainted in dark blue with black and yellow "Chevron Safety Stripes" on its headstocks. It also had "Transtec Engineering Dunedin" on the side of the long hood.^[14]