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North Island Main Trunk
Map of the North Island Main Trunk Railway
Info
Type	Main line
System	New Zealand railway network
Status	Open
Locale	North Island New Zealand
Terminals	Auckland Wellington
Operation
Opened	6 November 1908
Owner	ONTRACK (formerly Toll NZ, Tranz Rail, New Zealand Rail Limited, New Zealand Railways Corporation, New Zealand Railways Department)
Operator(s)	Toll Rail, Tranz Scenic, Tranz Metro (Wellington), Veolia (Auckland)
Character	Main line
Rolling stock	None specific
Technical
Line length	680km
No. of tracks	Two from Wellington - Pukerua Bay, Auckland - Hamilton, one Hamilton - Palmerston North.
Gauge	3 ft 6 in (1,067 mm)
Operating speed	Maximum speeds of 120km/h

North Island Main Trunk railway route map

Legend 0.0 Auckland Britomart Transport Centre Eastern Line Mission Bush Branch Glenbrook Vintage Railway 51.3 Pukekohe Glen Afton Branch Huntly Ngaruawahia Glen Massey Branch Te Rapa Start of AC electrification Hamilton East Coast Main Trunk Railway Te Awamutu Otorohanga Te Kuiti Waitete viaduct Stratford - Okahukura Line Taumarunui Whanganui River bridge Raurimu Raurimu Spiral National Park Makatote viaduct Manganui viaduct Mangaturuturu viaduct Taonui viaduct Hapuawhenua viaduct Raetihi Branch Ohakune Tangiwai Bridge Site of the Tangiwai disaster Waiouru Taihape Utiku North Rangitikei Viaduct Mangaweka Viaduct South Rangitikei Viaduct Mangaweka Mangaweka deviation Makohine viaduct Marton - New Plymouth Line Marton Fielding Palmerston North - Gisborne Line Palmerston North End of AC electrification  ?.? Foxton Branch Milson deviation Wellington - Manawatu Line Paraparaumu End of DC electrification Paraparaumu Line 681.0 Wellington Wellington Railway Station

In the 1930s the Wellington end of the NIMT was deviated from Wellington to Tawa Flat by the construction of the Tawa Flat deviation, including two long tunnels. The deviation is the centre two tracks, with the Wairarapa Line's Ngauranga station in the background, alongside State Highway 1.

EW 1805 hauling DC 4611 near Paekakariki on the electrified Wellington section of the NIMT

Some trains are hauled by diesels. Here a DC hauls the Overlander.

EF 30163 hauling The Overlander on the 25 kV AC electrified section of the NIMT.

The northern terminus of the NIMT, Britomart Transport Centre

The southern terminus of the NIMT, Wellington railway station

The North Island Main Trunk line (NIMT) connects Auckland and Wellington, the two major cities of New Zealand's North Island. The line is the standard New Zealand gauge of 1067 mm (3 ft 6 in). A train going north, towards Auckland, is an "up" train with an even number, and one heading southwards is a "down" train with an odd number. Distances are measured from Wellington to Auckland. The line is 680 kilometres (423 mi) long and includes the famous Raurimu Spiral.

Auckland's first railway southwards was the 13 km (8 mi) line between Point Britomart and Onehunga, opened in 1873. It included what is now the Onehunga Branch, at 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 opening on 13 August 1877. The line from Ngaruawahia was extended to Frankton by December 1877, and to Te Awamutu in 1880. An economic downturn and protracted negotiations with local Maori stalled construction for the next five years, and Te Awamutu remained the operating railhead for some time.

From Te Awamutu it was proposed that the line be built either via 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, on 6 November 1908; the central section was the most difficult to construct. It required crossing the North Island Volcanic Plateau with its deep ravines. This required the construction of nine viaducts and the world-famous Raurimu Spiral. The last spike was ceremonially driven by the Prime Minister, Sir Joseph Ward. The 'Last Spike' monument is at 39°16.44′S, 175°23.37′E, near Pokaka.

Main article: Wellington - Manawatu Line

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

Sections of the line have been upgraded and deviated several times. In the 1930s the old Wellington and Manawatu Railway Company line was deviated between Wellington and Tawa Flat, with most of the original line was retained as the Johnsonville Line. Also in the 1930s, the Auckland - Westfield section of line was deviated via Hobson's Bay. In the 1950s the line north from Tawa to Porirua and Plimmerton was duplicated and the section from Porirua to Plimmerton straightened by harbour reclamation. Between 1964 and 1966 the line was deviated from the centre of Palmerston North via Milson on the edge of the city. In 1981 the Mangaweka-Utiku deviation, with three viaducts, was opened. The central section of the line from Te Rapa near Hamilton to Palmerston North was electrified in the 1980s. Progressively tunnel clearances were increased and curves eased.

See also: Tawa Flat deviation

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.

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

Following the Second World War, railway services again 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 1,500 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 from his position 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 plants using imported diesel fuel.

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

The first part of the NIMT to be electrified was the Wellington - Paekakariki section 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. They were extended north to Paraparaumu in 1983, and will be extended to Waikanae by 2010.

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 report was written.

The electrification of the section received approval in 1980 and had 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. 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 1,100 - 1,200 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 analyses showed that this high rate of return gave the project robustness against lower traffic volumes than expected (the return remained positive even if traffic falls), against significant increases in construction cost, and against lower than expected rises in the diesel fuel price.

The Greater Wellington Regional Council has approved proposals to extend the 1500 V DC Wellington electrification north from Paraparaumu to Waikanae by the year 2010, in time for the introduction of new electric multiple units (EMUs). This will leave an 80.8 km (50 mi) gap to the central NIMT electrification, which starts at Palmerston North. Since the systems are different, multi-current locomotives would be required for through working should the two systems ever be joined - the current electric locomotives, the EF class, are AC only.

There have been numerous proposals to electrify the Auckland suburban rail network, some dating from the 1960s.^[1] Most of these proposals coincided with proposals to the electrify the NIMT in its entirety. The most recent proposals (2005), which the government has now determined to implement,^[2] are to electrify the network at 25 kV AC, the same system as on the central NIMT.^[3] This includes 49.5 km (31 mi) of the NIMT, the Southern line to Papakura, leaving a gap of 87.1 km (54 mi) to the central NIMT electrification, which begins at Te Rapa. Electrification may be extended south as the Auckland suburban system expands, but this will depend on further government funding.

See also: Public transport in Auckland - Core Network Upgrade

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

When it opened in 1908, the powerful 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. Instead, in 1932 the 4-6-4 K class was introduced, and later improved in 1939 with the K^A.

The introduction of the English Electric D^F class in 1951 began the end of the steam era, and in 1955 with the introduction of the D^A major withdrawals of steam locomotives began. 1972 saw the introduction of D^X locomotives and the Silver Fern railcars: the latter remained in service between Auckland and Wellington until 1991.

With electrification, the DX class was mainly re-assigned to the South Island and replaced by EF class electric locomotives, introduced in the late 1980s. Since then services have been worked mainly by the electrics, although some services are still diesel operated, such as paper pulp freight trains from Karioi to Wellington.

The following lines connect with the NIMT:

• Auckland-Newmarket Line, at Quay Park Junction.
• North Auckland Line, at Otahuhu.
• Mission Bush Branch, at Paerata.
• Glen Afton Branch, at Huntly.
• Glen Massey Branch (closed), at Ngaruawahia.
• East Coast Main Trunk, at Hamilton.
• Stratford - Okahukura Line, at Okahukura.
• Raetihi Branch (closed), at Ohakune.
• Marton - New Plymouth Line, at Marton.
• Taonui Branch (closed), at Taonui.
• Palmerston North - Gisborne Line, at Palmerston North.
• Foxton Branch (closed), at Longburn.
• Wairarapa Line, at Kaiwharawhara.
• Johnsonville Line, at Wellington.

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

Between 1963 and 1968, day-time 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.^[4] Organisations such as the Railway Enthusiasts Society run charters.

Tranz Scenic also operates the Capital Connection between Palmerston North and Wellington.

Main article: Transport in Auckland

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.

Main article: Public transport in Wellington

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

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.

• North Island Main Trunk: An Illustrated History by Bill Pierre (1981, AH & AW Reed), ISBN 0 589 01316 5.

• List of Auckland railway stations
• List of Wellington railway stations

• The Overlander; the current passenger service.
• A history of the NIMT & Overlander, with video & sound clips
• The Raurimu Spiral
• NZ Engineering Heritage NIMT page