North Island Main Trunk

North Island Main Trunk
North Island Main Trunk

Map of the North Island Main Trunk Railway
Type Heavy rail
System New Zealand railway network
Status Open
Locale North Island, New Zealand
Termini Wellington Railway Station
Auckland Britomart Transport Centre
Opened 14 August 1908 (railheads meet)
6 November 1908 (official opening)
14 February 1909 (line completed)
Operator(s) KiwiRail
Tranz Scenic
Tranz Metro (Wellington to Waikanae)
Veolia (Auckland to Pukekohe)
Character Main line
Rolling stock EF class electric locomotives (Te Rapa - Palmerston North)
Line length 681 km (423 mi)
No. of tracks Triple track Wellington - Wairarapa Line junction; double track Wairarapa Line junction -Pukerua Bay, Paekakariki-Waikanae, Hamilton-Te Kauwhata, Amokura-Auckland; remainder single track
Track gauge 1,067 mm (3 ft 6 in) Cape gauge
Electrification 1500V DC overhead Wellington - Waikanae
25kV 50Hz AC overhead Palmerston North - Te Rapa
25kV overhead under construction (Papakura - Britomart)
Operating speed 120 km/h maximum
Highest elevation 832 metres (2,730 ft)

The North Island Main Trunk (NIMT) is the main railway line in the North Island of New Zealand. The line links the nation's capital Wellington, with the largest city Auckland, via Paraparaumu, Palmerston North, Taihape, National Park, Taumarunui, Te Kuiti, Hamilton, and Pukekohe.

The NIMT is 681 kilometres (423 mi) in length, built to the standard New Zealand rail gauge of 1,067 mm (3 ft 6 in). Most of the line is single track with frequent passing loops, with double track existing for most of the distance between Wellington and Waikanae, and Hamilton and Auckland. Around 460 kilometres (290 mi) of the line is electrified: 55 km at 1500 V DC between Wellington and Waikanae, and 412 km at 25 kV AC between Palmerston North and Te Rapa in Hamilton. The 34 km between Papakura and Britomart is currently being electrified as part of the Auckland railway electrification.

The first section of what became the NIMT opened in 1873. The construction of the line began in 1885, and was completed in 1908 and was fully operational by 1909. The line is credited for having been an economic lifeline for the young nation, and for having opened up the centre of the North Island to European settlement and investment.[1] In the early days, a passenger journey along the whole length could take more than 20 hours, today, the remaining tourist services today take approximately 12 hours between Auckland and Wellington.[2]

The North Island Main Trunk has been described as an "engineering miracle", with numerous engineering feats such as viaducts, tunnels and spirals built to overcome large local elevation differences with grades suitable for steam engines.




Auckland to Te Awamutu

Auckland's first railway southwards was the 13 km (8.1 mi) line between Point Britomart and Onehunga, opened in 1873. It included what is now the Onehunga Branch from Penrose, branching off the line intended to be built to the Waikato, possibly to support the Invasion of the Waikato. From Penrose the line was extended south to Mercer by 20 May 1875, with 29 km (18 mi) from Ngaruawahia being constructed by the Volunteer Engineer Militia and opened on 13 August 1877. It was extended to Frankton by December 1877, and to Te Awamutu in 1880. An economic downturn stalled construction for the next five years, and Te Awamutu remained the operating railhead. There were also protracted negotiations with local Māori, and the King Country was not accessible to Europeans until 1883.

Wellington to Marton

The Wellington-Longburn (near Palmerston North) section was constructed between 1881 and 1886 by the Wellington and Manawatu Railway Company (WMR). The company was acquired by the New Zealand Railways Department in 1908.

The Longburn to Marton section of the line was constructed as part of the Foxton to Wanganui railway line.

Central North Island

From Te Awamutu it was proposed that the line be built via either Taupo (see Taupo Railway Proposals) or via Taumarunui, the eventual route. Construction of the final central section of line began on 15 April 1885, when Wahanui Maniopoto paramount chief turned the first sod outside of Te Awamutu. It was 23 years before the two lines met, as the central section was difficult to survey and construct. The crossing of the North Island Volcanic Plateau with deep ravines required the construction of nine viaducts and the world-famous Raurimu Spiral. By the beginning of 1908, there was a 39 km (24 mi) gap between Erua and Ohakune, with a connecting horse-drawn coach service. From Ohakune south to Waiouru the Public Works Department operated the train, as this section had not yet been handed over to the Railways Department.


The gap was closed on 7 August 1908 for the first through passenger train, the 11-car Parliamentary Special carrying the Prime Minister Sir Joseph Ward and other parliamentarians north to see the American Great White Fleet at Auckland.[1] But much of the new section was temporary, with some cuttings north of Taonui having vertical batters and some unballasted sections of track. Ward drove the last spike on 6 November 1908. The 'Last Spike' monument is at Manganui-o-te-Ao 39°16.44′S 175°23.37′E / 39.274°S 175.3895°E / -39.274; 175.3895, near Pokaka. A two-day NIMT service started on 9 November, with an overnight stop at Ohakune.

On 14 February 1909 the first NIMT express left Auckland for Wellington, an overnight trip scheduled to take 19 hours 15 minutes, with a sleeping car, day cars with reclining seats, and postal/parcels vans. The dining car went on the north express from Wellington to Ohakune, then transferred to the south-bound express, so avoiding the heavy gradients of the central section.

Track upgrades

Several sections of the line have been upgraded and deviated:

In 1930 the Westfield deviation was opened, creating a new eastern route from Auckland to Westfield via Glen Innes and Hobsons Bay, running into the new Auckland Railway Station and providing better access to the Port of Auckland. The original section between Auckland to Westfield via Newmarket then ceased to be part of the NIMT. The section from Auckland to Newmarket became the Auckland-Newmarket Line while the section between Westfield and Newmarket became part of the North Auckland Line (NAL) between Westfield to Whangarei.

In 1935 the Tawa Flat deviation was opened, bypassing most of the original WMR line between Wellington and Tawa. Constructed to alleviate issues with increasingly heavier freight traffic on the steep twisting original route, it was built as double track, with a pair of tunnels under the Wellington hills and later electrified at 1500V DC. Most of the original line has been retained as the Johnsonville Line.

In the 1950s the line north from Tawa north to Pukerua Bay was also duplicated. The section between Porirua to Plimmerton was straightened at the same time by reclaiming land along the eastern shore of Porirua Harbour.

Between 1964 and 1966 the line was deviated away from the centre of Palmerston North to run via Milson on the edge of the city. In 1967 the floors of the tunnels on the original WMR section between Paekakariki and Pukerua Bay were lowered to enable the DA class locomotives to pass through and travel all the way to Wellington.

Between 1973 and 1981 a major deviation was built between Mangaweka and Utiku in the central section. This deviation required the construction of three new viaducts, all over 70m tall, to cross the Rangitikei and Kawhatau rivers.

The central section of the line, from Te Rapa near Hamilton to Palmerston North, was electrified at 25 kV AC between 1984 and 1988 as part of the ‘Think Big’ government energy programme. In addition to the electrification work some tunnels were opened out or bypassed by deviations while in others clearances were increased. As well as this some curves were also eased. The section between Ohakune and Horopito was completely realigned with three viaducts replaced to handle higher loads and speeds. The most notable bridge replaced was the original curved wooden viaduct at Hapuawhenua by a modern concrete structure, though the original has been restored as a tourist attraction.

In 2011 work to duplicate the line between Paekakariki and Waikanae was completed as part of the upgrade and expansion of the Wellington suburban network.


Electrification of the NIMT was mooted by electrical engineer Evan Parry in the first volume of the New Zealand Journal of Science and Technology in November 1918. In light of a national coal shortage following World War I, Parry argued that the network was under great strain due to ever-increasing volumes of freight, and the use of steam traction was partly to blame. Parry also noted that there was great potential for cheap hydro-electricity generation in the central North Island to power electrification.

The first part of the NIMT to be electrified was the Wellington-Paekakariki section to Paekakariki via the Tawa Flat deviation in 1940, at 1500 V DC. Electric traction in this section is now used only by Tranz Metro for its suburban passenger services on the Kapiti Line, and was extended to Paraparaumu in 1983 and Waikanae in 2011.

From 1948 to 1951 the General Manager of the Railways Department, Frederick Aicken, advocated electrification of the entire line, despite protests from his engineering staff.

Following the Second World War railway services suffered due to skill and coal shortages. Skilled staff sought employment opportunities elsewhere in the economy. Aicken had previously been Staff Superintendent and Chief Legal Advisor to the Department, and considered using diesel locomotives for trains on the NIMT to be too expensive. He turned his attention to electrification, mainly because be saw that it could relieve the coal situation and prevent high expenditure on imported fuels.

He commissioned a study into electrification, which concluded that a low frequency alternating current system could be cheaper than the 1500 V DC system. Aicken sent a technical mission of four senior officers overseas in March 1949, and travelled overseas himself to negotiate a tentative contract with a British construction company. The Chief Mechanical Engineer and Chief Accountant specified and costed the system and Aicken was able to complete a substantial report justifying the NIMT electrification and submit it to the Government. Officers from New Zealand Treasury and the Ministry of Works and two experts from Sweden commented on the proposal and in December 1950 the Government granted approval in principle and agreed to appoint Thelander as a consultant. However, Aicken fell out with the then National Government, and retired as General Manager in July 1951. With the change in regime the electrification proposal disappeared.

A key assumption of Aicken's report was that traffic on the NIMT would grow by 50% from 1948 to 1961. Since a diesel-electric locomotive was in fact a travelling power station, the savings through electrification compared to diesel could be regarded as the difference between the cost of buying bulk electrical energy generated substantially from New Zealand resources and the cost of generating electricity in small plant using imported diesel fuel.

However, the Royal Commission on Railways created following Aicken's tenure rejected the report's findings. Aicken's successor, H.C. Lusty, terminated the tentative contract and ordered DA class diesel-electric locomotives.

The 411 km (255 mi) section between Palmerston North and Hamilton was electrified at 25 kV 50 Hz AC, opened in June 1988 as one of the previous Muldoon National Government's "Think Big" energy development projects. An overall cost in excess of $100 million had been projected, with some 40% being for the locomotives, but the final cost was about $250 million. The overall economics of the project were greatly undermined by the fall of the price of oil in the 1980s and the deregulation of land transport, which removed the long-distance monopoly NZR held when the cost benefit report was written.

The electrification of the section (which had its genesis in a study group set up in June 1974 to report on measures to be taken to cope with increasing rail traffic volumes) received approval in 1980. This led to a technical study carried out with assistance from the Japan Railway Technical Service. The report stated that increases track capacity would be created by electrification because such traction is faster and more powerful. The report stated, for example, that whereas a diesel locomotive could haul 720 tonne trains at 27 km/h (17 mph) up the Raurimu Spiral, an electric locomotive could haul 1100-1200 tonne trains at 45 km/h (28 mph), cutting 3–5 hours off journey times. Less fuel would be needed and employing regenerative braking in electric locomotives lowers the fuel consumption further. Electrification's advantages were reflected in the economic evaluation in the report, which showed a rate of return of 18%. Sensitivity analysis showed that this high rate of return gave the project robustness against lower traffic volumes than expected (the return remained positive even if traffic fell), against significant increases in construction cost, and against lower than expected rises in the diesel fuel price. Part of the project included replacing the old copper wire communications system with a new fiber optic communications cable (due to interference caused by AC power with the DC copper wire system). The fiber optic cable was installed from Wellington to Auckland. In 1994 New Zealand Rail Limited sold the fiber optic cable to Clear Communications for telephone traffic, leasing it back for signalling traffic.[3]

A further extension of the Wellington electrification was opened on 20 February 2011. Funded by the Greater Wellington Regional Council, the extension coincides with the delivery of new Matangi electric multiple units.[4]

The future

With the opening of the extension to Waikanae, there are now calls for the electrification to be extended again by 15 km (9.3 mi) to Otaki.[5]

There is a 80.8 km (50.2 mi) gap from Waikanae to the central NIMT electrification, which starts at Palmerston North. If the electrification is extended to Otaki, there will be a 65 km (40 mi) gap. Since the systems are different, multi-current locomotives or multiple units (such as the Japanese EH500) would be required for through working should the two systems be joined (the EF class electric locomotives are AC only and the EO class locomotives are DC only), or the Kapiti Line and the Wellington suburban network would need to be re-electrified to 25 kV AC.

There have been numerous proposals to electrify the Auckland suburban rail network, some dating from the 1960s.[6] Most of these proposals coincided with proposals to electrify the NIMT in its entirety. The most recent proposals (2005), which the government has decided to implement,[7] are to electrify the network at 25 kV AC, the same system as on the central NIMT.[8] This includes 49.5 km (30.8 mi) of the NIMT (the Eastern Line from Britomart to Papakura), leaving a gap of 87.1 km (54.1 mi) to the central NIMT electrification at Te Rapa, north of Hamilton. Electrification may be extended south as the Auckland suburban system expands, but this will depend on further government funding. In February 2008 Auckland Regional Council Chairman Mike Lee suggested the initial electrification might be extended to Pukekohe, leaving a 60 km gap to Te Rapa.[9] Work on electrification of 80 km of the Auckland network, including 33 km of the NIMT between Papakura and Britomart, began in 2010 and is to be completed by 2013.[10]


On 6 August 2008 at 9 am a train including the 100-year-old carriage AA1013 departed Wellington in a re-enactment of the original 7 August 1908 Parliamentary Special carrying the Prime Minister Sir Joseph Ward to Auckland.[11] It carried the Prime Minister, stopping overnight in Taihape before continuing on to Taumarunui and then Auckland. Tickets were by invitation only. The carriage was restored by the Mainline Steam Trust.

A series of stamps were issued to commemorate the centennial, see Stamps:

  • 50c - Last Spike Ceremony Manganui-o-te-ao - a photo of actual event [12]
  • $1.00 - Taumarunui, 1958 - photo of steam locomotive KA 947 pulling into the old railway station.
  • $1.50 - Makatote Viaduct, 1963.
  • $2.00 - Raurimu Spiral, 1964.
  • $2.50 - Overlander, Hapuawhenua Viaduct, 2003.


The North Island Main Trunk has been described as an "engineering miracle", with numerous engineering feats especially along the Rangitikei River and on the North Island Volcanic Plateau. This included the building of the famous Raurimu Spiral to allow trains to manage the steep grade from the Whanganui River valley onto the Volcanic Plateau. The NIMT also contains nine major viaducts, of which five are over 70 metres (230 ft) high - Makohine (73 m/240 ft), South Rangitikei (78 m/256 ft), Kawhatau (73 m/240 ft), North Rangitikei (81 m/266 ft), and Makatote (79 m/259 ft).

The NIMT's entire 681 km length totals 352 bridges, and includes 14 tunnels.[2]

Rolling stock

Due to its high volume and high value of traffic to NZR and the steep grades in the central section, the NIMT has used the most powerful locomotives in New Zealand.


When the NIMT opened in 1909, the powerful 4-8-2 X class was introduced to handle heavy traffic over the mountainous central North Island section. Four G class Garratt-type locomotives were introduced in 1928, but these locomotives were not as effective as anticipated. In 1932 the 4-8-4 K class was introduced, and later improved in 1939 with the KA.

The introduction of the English Electric DF class in 1954 began the end of the steam era, and in 1955 with the introduction of the DA major withdrawals of steam locomotives began. 1972 saw the introduction of DX locomotives and the Silver Fern railcars: the latter remained in service between Auckland and Wellington until 1991.

With electrification and the introduction of the EF class electric locomotives in the late 1980s, the DX class was mainly re-assigned to other areas of the network, including hauling the coal freight on the Midland Line in the South Island. Since then services between Te Rapa and Palmerston North have been worked mainly by the electrics, although some services are still diesel operated, such as those originating from or terminating on other lines, or originating from within the central section like the paper pulp freight trains from Karioi to Wellington.

Current stock

The North Island Main Trunk today is operated by a combination of diesel and electric locomotives and multiple units.

As of 2011, regular rolling stock on the NIMT include:

Connecting lines

The following lines connect with the NIMT:

Passenger services


From the opening of the line there have been regular passenger services between Wellington and Auckland.

Between 1963 and 1968 daytime services on the line were known as the Scenic Daylight. In 1968, an RM class 88-seater railcar was refurbished and repainted in a distinctive blue scheme that led to it being nicknamed the Blue Streak. It initially operated an unsuccessful service between Hamilton and Auckland in early 1968, and was transferred to the Auckland-Wellington run on 23 September 1968.

In 1971 NZR introduced the Silver Star, a luxury sleeper train. The service was not economically viable, and was withdrawn in 1979. Much more successful was the Silver Fern, a daytime railcar service, introduced in 1972 to replace the "Blue Streak". This service was withdrawn in 1991 and replaced by The Overlander, now operated by Tranz Scenic. On 25 July 2006 Toll announced that the Overlander would cease at the end of September 2006, but on 28 September 2006 the train's continuation on a limited timetable was announced.[13] It now runs daily each way during the summer months and thrice-weekly for the balance of the year.

Tranz Scenic also operates the weekday once-daily return Capital Connection between Palmerston North and Wellington.

Organisations such as the Railway Enthusiasts Society run charters.

Auckland suburban

Within the Auckland Region between Britomart and Pukekohe suburban trains runs on the NIMT at regular intervals. Services terminate at Britomart Transport Centre, all using the NIMT from Quay Park Junction.

Eastern Line (Pukekohe, Papakura and Otahuhu to Britomart via Glen Innes) trains run along the NIMT between Pukekohe and Britomart.

Southern Line (Pukekohe, Papakura and Otahuhu to Britomart via Newmarket) trains run along the NIMT from Pukekohe to Westfield, the North Auckland Line to Newmarket, and the Auckland-Newmarket Line to the NIMT at Quay Park junction.

Wellington suburban

Wellington's suburban network, operated by Tranz Metro, includes the southern portion of the NIMT between Wellington and Waikanae, known as the Kapiti Line. Services terminate at Wellington railway station.

Record runs

Record runs on the NIMT from Auckland to Wellington were the 1960 Moohan Rocket (train) of 11 hours 34 minutes in 1960, and the Standard railcar time of 9 hours 26 minutes (running time 8 hours 42 minutes) in 1967.


See also


  • North Island Main Trunk: An Illustrated History by W.A. Pierre (1981, A.H. & A.W. Reed), ISBN 0 589 01316 5.
  1. ^ a b Dearnaley, Mathew (9 August 2008). "Steel backbone an economic lifeline". The New Zealand Herald. Retrieved 1 November 2011. 
  2. ^ a b "Auckland to Wellington: It's the journey that counts". The New Zealand Herald. 28 June 2011. Retrieved 28 June 2011. 
  3. ^ "September 1994 decisions". Campaign Against Foreign Control of Aotearoa. 
  4. ^ "KiwiRail - Wellington Projects". 22 September 2010. 
  5. ^ Nigel Wilson. "Raumati Station Now". Retrieved 2011-02-23. 
  6. ^ The Railways of New Zealand by Churchman and Hurst
  7. ^ New Zealand Herald. "$1b Auckland rail upgrade powers ahead". Retrieved 2007-05-21. 
  8. ^ ARTAPDF
  9. ^ "Electric train lines may reach Hamilton". The New Zealand Herald. 6 June 2008. Retrieved 2008-07-05. 
  10. ^ "KiwiRail awards Auckland rail electrification contract". Radio New Zealand. 14 January 2010. Retrieved 14 January 2010. 
  11. ^ "Unique rail carriage on track for re-enactment". Wairarapa Times-Age. 28 February 2008. Retrieved 2008-07-05. 
  12. ^ "Stamp Issue Celebrates Main Trunk Line Centenary". New Zealand Post Stamp issue. Retrieved 24 September 2008. 
  13. ^ "Overlander to continue running". New Zealand Herald. 28 September 2006. Retrieved 2007-10-15. 

External links

Wikimedia Foundation. 2010.

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