New Zealand DX class locomotive

The New Zealand DX class locomotive is a type of diesel-electric locomotive that currently operates on New Zealand's national railway network. There are 49 of the locomotives and all are owned by KiwiRail. They have a Co-Co wheel arrangement.

Built by GE Transportation in Erie, Pennsylvania, United States, they were introduced to New Zealand between 1972 and 1976. The class is based on the General Electric U26C model, a narrow-gauge version of the GE U23C model, which in itself is a V12 version of the 16V GE U30C.

The locomotives are regarded as one of the most successful purchases in NZR's history. They have seen several upgrades since their introduction and three sub-classes now exist: the DXB, DXC and DXR. In 2025, it was announced that 46 of the locomotives had been sold to a South African purchaser, Traxtion. The first eight locomotives arrived in South Africa in July 2026. The final DX class locomotives are planned to be withdrawn by June 2027.

Introduction The DX class was introduced in response to a requirement for a more powerful locomotive to handle traffic on the North Island Main Trunk (NIMT). Before their introduction, the heaviest freight and passenger trains on the line required two members of the DA class to haul them. The DX class could haul heavier and faster trains than two DA locomotives, even though they produced 70 kilowatts less than two DA locomotives could. A single DX weighed 97.5 tonnes compared to the two DA class locomotives' combined weight of 162 tonnes.

Tenders opened for what was to become known as the DX class in December 1969. The order for the first 15 DX class locomotives was placed on 24 August 1970. They were the first locomotives built by General Electric in New Zealand and were the most powerful ever used in New Zealand at the time of their introduction.

Classification The classification of the new locomotives was announced as the "DX" class. Diesel mainline locomotive classes begin with "D", followed by another letter. "X" was out of sequence, as the previous class introduced was the Mitsubishi DJ class in 1968. Up to the DX class introduction, all classes had used letters A to J, and shunting locomotives used S. The use of X for the DX class was a specific reference to the NZR X class locomotives of 1907, which were specifically introduced for use on the North Island Main Trunk, and were much more powerful than any previous locomotive class. NZR chose DX classification for practical reasons as well; the next locomotive classification in sequence (DK class) would have grouped a General Electric supplied locomotive after a Mitsubishi supplied class, secondly, the X classification distinguished the class in terms of power output.

First phase The first 15 members of the class (DX 2600 – DX 2614) arrived in Auckland Harbour in February 1972.

Their introduction led to a dispute over additional pay between New Zealand Railways and the Engine Drivers, Firemen and Cleaners' Association (then the trade union representing NZR locomotive staff). The union argued that more powerful locomotives meant less work for its members and successfully took NZR to the Government Railways Industrial Tribunal for additional pay in July 1972. The extra pay was known as a "horsepower allowance".

The locomotives were progressively introduced into service from November 1972.

Initially, the class were confined to the North Island Main Trunk as their 16.25-tonne axle load was too heavy for many of the bridges on the other lines. As it was, several bridges and viaducts on the NIMT had to be strengthened to take the weight of the locomotives. Their prime movers were found to be less reliable than NZR was accustomed to with its other locomotives.

Second phase The first DX class locomotives proved to be a success. With bridges progressively strengthened throughout the North Island, and to further increase capacity on the NIMT in particular, 34 more members of the class were introduced in 1975 and 1976. The second phase DX had a number of improvements, including additional dynamic braking, larger sandboxes and a better excitation control system.

In service

History

The DX class was initially used for heavy freight trains on the NIMT, especially on the central section where the power was needed. Most of the 49 class members in service by 1976 were used on this line, but a few also operated between Palmerston North and New Plymouth via the Marton - New Plymouth Line most days of the week, and also occasionally on passenger trains between Wellington and Masterton on the Wairarapa Line. In 1974, a DX travelled on the North Auckland Line as far north as Whangarei, and there-after they saw occasional use in Northland in the late 1970s and early 1980s, but it did not have any regular assignments there.

From their introduction in 1972, a member of the class was assigned to haul the prestigious Silver Star overnight NIMT passenger express. Previously, the train required two DA class locomotives. The DX class was also used on the Northerner overnight passenger train when it was introduced in November 1975.

In June 1988, a major reshuffle of the mainline locomotive fleet took place nationwide as a result of the opening of the NIMT electrification and introduction of the EF class to handle the central section. For the DX class, this meant leaving the upper North Island and being split into two fleets for service between Wellington, Gisborne and New Plymouth, and one in Dunedin. This was the first use of the class on the Palmerston North - Gisborne Line and the northern section of the Wairarapa Line between Masterton and Woodville. At the same time, experiments began with DX class locomotives in the then electrified Otira Tunnel. While the initial tests were unsuccessful, later testing in 1991 found that modifying the locomotives with special air intake ducts and adding ventilation fans would allow the DX class to be used without electric locomotives.

In the mid-1990s, a small number of DXs returned to Auckland for use between Auckland and Tauranga via the East Coast Main Trunk, on the Kinleith Branch and regular service between Auckland and Whangarei. This was the first use of the class in regular service east of Hamilton. In 2000, a DX ventured north of Whangarei, which remains the last expansion phase of DX class territory.

Current

The DX class is still used primarily on heavy freight trains. The class now operate in the South Island, predominantly hauling coal trains between the West Coast mines and the port of Lyttelton near Christchurch. The trains consist of up to 30 CE and CB class hopper wagons each carrying up to 52 tonnes of coal, and require six members of the class to haul the train up the 3% (1 in 33) west-east grade of the Otira Tunnel, and two members to haul it on the other sections of the line. These services are now exclusively hauled by the DXC sub-class. The class is also involved in general freight operations and is employed periodically to haul the TranzAlpine and Coastal Pacific passenger trains.

In the North Island, the DXB sub-class were the primary haulers of milk trains to Fonterra's Whareroa factory near Hāwera on the MNPL, usually operated in pairs to haul these trains up the 1 in 35 Westmere Bank north of Wanganui.

A small number, including both DXRs, were based in the upper North Island, primarily in general freight use on the ECMT. With the allocation of the new DL class locomotives to that area, these locomotives were transferred to the South Island in late 2011.

The class were also periodically used to haul through trains on the central NIMT when EF locomotives were unavailable or the electrification required maintenance. They were the primary haulers of the Capital Connection service between Palmerston North and Wellington.

In October 2013, KiwiRail reassigned six DXBs to the South Island due to the commissioning of the second batch of the DL class, leaving three assigned in the North Island. All of these locomotives, including the locomotives assigned to the South Island prior October 2013, were transferred back to the North Island to cover for the DL locomotives in March 2014, as the DL class were temporarily withdrawn from service after they tested positive for asbestos. All locomotives are now operating in the South Island as of March 2020.

Numbering The DX class was originally numbered from 2600 to 2648 – which in common with NZR practice of the time was based on power output (2600 hp).

With the introduction of the computerised Traffic Monitoring System (TMS) in 1979, the class was soon renumbered. The DX class received four-digit numbers starting with 5, in which the fourth number is a check digit for the number. The locomotives were numbered in order, with DX 2600 renumbered DX5016 (6 being the check digit) and DX 2648 renumbered DX5517. The numbers 500x, 515x, 534x and 549x were not used as these numbers do not generate a valid check digit, and DX 2639 never received a TMS number as it had been withdrawn by then.

The DXB and DXC sub-classes have kept their original TMS numbers, while the DXR class received new TMS numbers beginning with 8, numbered irrespective of their DX number. DX5045 received a new TMS number using the DXB algorithm (5520) when it was upgraded and returned to service following being involved in a fatal derailment at Te Wera in 2002 (when re-introduced into service, the DXB classification was used to denote what is now the DXC sub-class).

Livery

Upon introduction, all the DX class members were painted in a livery consisting of the locomotive body painted orange, except for a chrome yellow segment that curved down from the top of the locomotive's long hood and ran back to its trailing end. The cheat line separating the orange from the yellow was approximately halfway up the side of the locomotive. The reasons for this livery have not been established. This livery was known as "Clockwork Orange" after the Stanley Kubrick film "A Clockwork Orange." The bogies and fuel tank were painted a flat grey colour and North American automatic couplers were fitted – these being soon changed to a beefed-up version of the NZR chopper-type.

Between October 1976 and 1986, the entire class was repainted in the International Orange "Fruit Salad" livery – red, grey, and yellow, which most of the class wore until the end of the decade. This livery had the road numbers displayed on the sides of the locomotives in large white numbers with DX 2612 the first to be painted as such. Since then, members of the DX class have received liveries including Cato Blue (Fruit Salad with blue instead of red), Bumble Bee (black and yellow), Corn-Cob (green and yellow) and the KiwiRail phase 1 and 2 schemes (grey, orange or red, and yellow). No DXs remain in the Fruit Salad, Cato Blue, Bumble Bee and Corn Cob liveries.

Upgrades The locomotives received an upgrade during 1988 with the introduction of single-manning to improve visibility for the driver, with a large single front window replacing the original two small windows.

Fire suppression Between 2013 and 2016, the DXC class were fitted with fire suppression to run the TranzAlpine through the Otira Tunnel on the Midland Line due to a change in requirements resulting from the Commission of Inquiry in the Pike River Mine disaster, and as well on any other passenger trains on the Main North and Main South lines. Because of this, the number of Otira bankers have gone from three to five, which allows any locomotive without the system to be shut down. In mid 2016, the number of bankers were reduced from five to four. , all 32 locomotives have been fitted with fire suppression.

Sub-classes

The classifications DXB and DXC reflect modifications that have been carried out to the fleet. These include heavier drawgear, uprated engines, new cabs, (some have received DFT-style low hoods) and higher power traction motors.