New Zealand DX class locomotive

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New Zealand DX class locomotive
DXB5143 at Platform 9 wgtn 1stJuly2008.jpg
DXB 5143, the first locomotive to be painted in the KiwiRail livery
Type and origin
Power typeDiesel-Electric
BuilderGeneral Electric, United States
ModelGE U26C
Build date1972–1975[1]
 • UICCo-Co
Gauge3 ft 6 in (1,067 mm)
Length16.9 metres (55 ft 5 in)
Width2.74 metres (9 ft 0 in)
Height3.70 metres (12 ft 2 in)
Axle loadDX 16.25 t (15.99 long tons; 17.91 short tons)
DXR 17.5 t (17.2 long tons; 19.3 short tons)
Adhesive weightDX 97.5 t (96.0 long tons; 107.5 short tons)
DXR 105 t (103 long tons; 116 short tons)
Loco weightDX 97.5 t (96.0 long tons; 107.5 short tons)
DXR 105 t (103 long tons; 116 short tons)
Prime moverGeneral Electric 7FDL-12
RPM range400–1050 rpm
Engine typeV12 Diesel engine
AlternatorGeneral Electric GTA-11
Traction motorsSix
Transmission25/64 gear ratio
Performance figures
Maximum speed105 km/h (65 mph)
Power outputDX/DXB/DXC
2,050 kW (2,750 hp) original
2,240 kW (3,000 hp) uprated[2][3]
2,420 kW (3,250 hp)
Tractive effortDX 259 kN (58,000 lbf) continuous
Number in class49
Numbers2600–2648 (original)
5016–5520 (TMS)
DXR 8007, 8022
Nicknames"Dixies" (DX)
First runDX 1972
DXR 1993
DXC 1997
Disposition46 in service
2 rebuilt as DXR
1 scrapped

The New Zealand DX class locomotive is a class of 49 Co-Co diesel-electric locomotives that currently operates on New Zealand's national railway network.

Built by GE Transportation in Erie, Pennsylvania, United States,[4] they were introduced to New Zealand between 1972 and 1976.[1] The class is based on the General Electric U26C model,[1] a narrow-gauge version of the GE U23C model. The U26C is also used in South Africa (see South African Class 34-900), Brazil, Kenya, Tanzania and Zambia.

The locomotives have seen several upgrades since their introduction and three versions now exist: the DXB, DXC and DXR.


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).[1] Before their introduction the heaviest freight and passenger trains on the line required two members of the 1,060-kilowatt (1,420 hp) DA class to haul them. The DX class could haul heavier and faster trains than two DAs, even though they produced 70 kilowatts less than the combined DAs, as the single DX weighed 97.5 tonnes compared to the two DAs combined weight of 162 tonnes.


There is no clear reason why the class was named the DX class. Diesel mainline locomotive classes begin with "D", followed by another letter - the mystery was why "X". Up to the DX class introduction, all classes had used letters A to J, and shunting locomotives used S. One possible explanation for the X was a reference to the 4-8-2 NZR X class steam locomotives, which ran on the central section of the NIMT between 1909 and 1957, and at the time of their introduction were the most powerful steam locomotives on NZR. Another possible explanation is that the 'X' was actually a 'K' - following on from the DJ class - but was misread and the designation changed to conform with the error.

First phase[edit]

The first 15 members of the class (DX 2600 - DX 2614) arrived in Auckland in February 1972.[5]

Their introduction led to a dispute between New Zealand Railways and the Enginedrivers, Firemen and Cleaners' Association (then the main trade union representing railway workers) over additional pay. The union argued 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 additional pay was known as a "horsepower allowance".[5]

They were progressively introduced into traffic in November 1972.

Initially, they were confined to the NIMT 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.

Second phase[edit]

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.

In service[edit]


DX 2612 (DX 5137) at Avondale in Auckland in the late 1970s. Note the two small windows in the locomotives cab, replaced in 1988 with a single window as a result of single-crewing.

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 ventured along the North Auckland Line as far north as Whangarei, and thereafter they saw occasional use in Northland in the late 1970s and early 1980s but 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 1975.

In 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 the South Island. 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.[6] 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.[6]

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.


Two DXC locomotives on a coal train from Ngakawau to Lyttelton crossing the Waimakariri River bridge

The DX class is still used primarily on heavy freight trains. The majority of 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 class hopper wagons each holding 52 tonnes of coal, and require five members of the class to haul the train up the 3% (1 in 33) west-east grade of the Otira Tunnel,[7] 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 are also involved in general freight operations, and also 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 Hawera on the MNPL, usually operated in pairs to haul these trains up the 1 in 35 Westmere Bank north of Wanganui. The class is also involved in other freight operations in the lower North Island, usually operating singly or in multiple with other locomotives.

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 are also periodically used to haul through trains on the central NIMT when EF locomotives are unavailable or the electrification requires 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.[8] All of these locomotives, including the units 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.[9] As of February 2019, only two DXBs are assigned in the North Island, with the remainder having been allocated to the South Island.


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

With the introduction of the computerised Traffic Monitoring System (TMS) in 1980, the class was renumbered. The DX class received four-digit numbers starting with 5, in which the fourth number is a check digit[10] for the number. The locomotives were numbered in order, with DX 2600 renumbered DX 5016 (6 being the check digit) and DX 2648 renumbered DX 5517. 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. DX 5045 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).


DX 5356 leaving Avondale in the late 1980s. The locomotive is painted in the International Orange or "Fruit Salad" livery of NZR from the late 1970s onwards. Note the single front window above the short hood.
DX 5097 in Cato Blue livery with Tranz Rail logo, in Auckland, 2001.
DXC 5258 in Toll Rail Corn-Cob livery at Otira in July 2008.

Upon introduction, all the DX class members were painted in "clockwork orange". The livery consisted of the locomotive body painted orange except for a yellow segment at the top of the locomotives - roughly the same shape and size as the orange segment on the original KiwiRail livery.

Between 1977 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.


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.

One locomotive, DXB 5074, has received a 2240 kW engine.[3]

Fire suppression[edit]

Between 2013 and 2016, the DXC class were fitted with fire suppression to run the TranzAlpine through the 8.5-kilometre (5.3 mi) 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 loco without the system to be shut down. In mid 2016, the number of bankers were reduced from five to four. As of December 2016, all 32 units have been fitted with fire suppression.


DXC 5241 hauling a Christchurch to Picton mixed freight train at Oaro

There are two sub-classes of the DX - DXB and DXC.

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.

The designation DXB denotes that the locomotive has been fitted with the Brightstar electronic traction control system, while DXC denotes that the locomotive has been additionally fitted with modified air intakes (“chutes”) as well as all the other upgrades including Brightstar. Thirteen of the original batch of 15 have been upgraded to DXB standard (DXC 5039 and DXC 5520 (nee 5045) being the exceptions), and most of those from the subsequent batches upgraded to DXC standard - exceptions being DX 2639 (long since withdrawn from service).

Generally the DXC sub-class is assigned to the South Island, as the modified air intakes were designed to assist in are useful for working the Midland Line, coal trains (see above) particularly in the formerly electrified Otira Tunnel section, whereas the DXB sub-class were predominantly assigned to the North Island. Following the introduction of the first twenty DL class locomotives, four DXBs were reassigned to the South Island for general freight service on the Main South Line, while DXC class locomotives have appeared in the North Island while on shakedown runs after overhaul.

The plain DX class is designated by GE as U26C, the newer upgrades are designated C26-MMI (2,750 hp DXB/DXC) and C30-MMI (3,250 hp DXB/DXC).


DXE class[edit]

In mid-2018, it was announced 15 DX class locomotives are to be overhauled, and given a electronic upgrade.[11] The locomotives are to be overhauled with 3,300hp-rated GE 7FDL-12 EFI diesel engine prime movers with electronic fuel injection. They will also be given the latest version of the Brightstar engine control system, new engine control and wiring harness, and new high capacity fuel tank, along with a new battery box assembly.[11]

Also involved in the overhauls will be the strengthening of the underframe, and fitting of new 2MN maintenance free draw gear, electronic braking system and full loco rewire and new engine oil coolers. The locomotives will be reclassified as DXE,[12] will have a newly designed long-hood (similar to the DXRs) fitted with chutes, and the short-hood will be lowered.[11] As of March 2019, the prototype, 5500, is still under overhaul. It is planned this will give the locomotives a life extension of 20 years.[11]

DXR class[edit]

DXR 8007 with KiwiRail logo, 2009. Note the MkII "Universal Cab" as originally fitted to DXR 8022
DXR 8007 with KiwiRail logo, 2009. Note the MkII "Universal Cab" as originally fitted to DXR 8022
DXR 8022 and DXB 5143 at Ethelton with a container train from Picton to Christchurch

In 1993, New Zealand Rail Limited undertook a significant rebuilding of DX 5362 into the first of what was to be a new sub-class, the DXR. The DX had been stored out of service at Hutt Workshops since early in 1989 suffering a cracked frame, and therefore was an ideal candidate for the rebuilding programme. Work began to fit the locomotive with a new 3,300 hp GE 7-FDL diesel engine, upgraded traction motors with a ratio of 5.17 to the then-standard DX ratio of 4.55, and a new design of "Universal Cab" with a shorter low hood and more angular appearance. The use of 'R' (like the DBR class) denotes that the new locomotive was a rebuilt DX.

The newly rebuilt DX received the number DXR 8007 when it entered service in 1993 along with the prototype DFT class rebuild, DFT 7008. Initially it was intended that New Zealand Rail would rebuild all of the DX class locomotives to DXR specifications similar to the programme of rebuilding of the DF class into the DFT class, but after the privatisation of New Zealand Rail Limited (renamed Tranz Rail in 1995) later in 1993, the new management decided not to undertake further DX class rebuilds, due to the cost.[13] One locomotive was however rebuilt to these original DXR specifications during the Tranz Rail years, DX 5310 in 2001 for its return to service following its derailment at Pukehou while hauling the Bay Express in 1995.[14] It did not though receive a new DXR style cab, so it retained its original DX classification until it was overhauled to DXC standards in 2010.

Following the purchase of Tranz Rail by Toll in 2003, the new management authorised the rebuild of DX 5235 - itself having been stored since being damaged in a collision in Christchurch in 2000 - which became DXR 8022. The new DXR featured minor differences in the carbody hood and a MkII version of the "Universal Cab" which was more boxy that the previous MkI variant as applied to DXR 8007. The new DXR rebuild was classified as DXR 8022 and entered service in late 2005. It was decided to rebuild DXR 8007 to match 8022 in the interests of standardisation, and so 8007 was again rebuilt at Hutt Workshops in 2006.

The two DXRs on the Waipara River Bridge with a freight train in November 2016

Upon each rebuild, GE classified 8022 (and reclassified 8007) as model C30-8Mi. In 2007, DXR 8022 was one of the locomotives involved in a biofuel trial using of a fuel mix of 5 per cent biodiesel and 95 per cent regular diesel over a period of six months.[15] With the introduction of the DL class locomotives into service the two DXRs were transferred to the South Island, and are now used between Middleton and Picton.

At 2,420 kilowatts (3,250 hp), the DXR class was the most powerful class of diesel-electric locomotive ever operated in New Zealand, until the introduction of the DL class in 2010, which surpassed the DXRs power output with 2,700 kilowatts (3,600 hp). As rebuilt by New Zealand Rail, DXR 8007 was classified by GE as their model C30-7M, while both 8007 and 8022 as rebuilt by Toll Rail are classified as model C30-8i.


As of 2017, only one DX class locomotive had been withdrawn from service. DX 2639 was involved in a crash south of the Parnell Tunnel near Newmarket station, at around 4:00pm on 23 March 1977. The locomotive was hauling a Wellington to Auckland express freight train when it crashed head-on into an Auckland to Helensville passenger train being hauled by DA 1426 that was on the wrong line. The cause was related to human error during a signalling failure. DX 2639 was subsequently written off and scrapped in September 1978[3] after less than a year in service.[16] In the early 1990s, a small group of DXs were withdrawn due to being surplus to requirements, but they were later returned to service.[17]

In August 2017, KiwiRail announced they were in discussions with global suppliers including General Electric, Electro-Motive Diesel, Alstom, CRRC and Stadler Rail to construct replacements for the remainder of the class. It was expected the first replacements would arrive in 2022/23.[18] However, with the decision to rebuild 15 locomotives as the DXE sub-class means the immediate need for new locomotives no longer exists.[11]

See also[edit]


  1. ^ a b c d McClare 1980, p. 24.
  2. ^ KiwiRail 2011, p. 21.
  3. ^ a b c Parsons 2002, p. 21.
  4. ^ Sinclair 1992, p. 9.
  5. ^ a b New Zealand Railway Observer - Class "DX" diesel-electric locomotives (Winter/Spring ed.). New Zealand Railway and Locomotive Society. 1972. p. 122.
  6. ^ a b "Rails". Southern Press. May 1997: 216. Cite journal requires |journal= (help)
  7. ^ "Friends in High Places". Off the Rails: A Love Story. Episode 4. 2005. TVNZ. TV One.
  8. ^ "Railfan". 20 (1). Triple M Publications. December 2013. ISSN 1173-2229. Cite journal requires |journal= (help)
  9. ^ "Railfan". 20 (1). Triple M Publications. March 2014. ISSN 1173-2229. Cite journal requires |journal= (help)
  10. ^ Sinclair 1992, p. 11.
  11. ^ a b c d e "Railfan". 25 (2). Triple M Publications. March 2019. ISSN 1173-2229. Cite journal requires |journal= (help)
  12. ^ "The Transport Worker - RMTU - In the midst of a growth wave" (PDF). Rail & Maritime Transport Union. March 2019. Retrieved 25 March 2019.
  13. ^ "Interview with Ed Burkhardt, 1993". Rails. Southern Press Limited: 94. November 1993. ISSN 0110-6155.
  14. ^ "Australasian pics".
  15. ^ "All Aboard for 'Bioloco' Ride". The Dominion Post. 2007-12-09. Retrieved 2008-10-09.
  16. ^ Churchman 1992, p. 92.
  17. ^ "Railfan". 2 (4). Triple M Publications. September 1996. ISSN 1173-2229. Cite journal requires |journal= (help)
  18. ^ "Railfan". 23 (4). Triple M Publications. September 2017. ISSN 1173-2229. Cite journal requires |journal= (help)

Further reading[edit]