The North Island Main Trunk (NIMT) is the main railway line in the North Island of New Zealand, connecting the capital city Wellington with the country's largest city, Auckland. The line is long, built to the New Zealand rail gauge of and serves the large cities of Palmerston North and Hamilton.
Most of the NIMT is single track with frequent passing loops, but has double track -
between Wellington and Waikanae, except for of single-track through tunnels between North Junction ( from Wellington) and South Junction, ( from Wellington), on the Pukerua Bay to Paekākāriki section, between Hamilton and Te Kauwhata (except for the single-track Waikato River Bridge at Ngāruawāhia), and between Meremere and Auckland Britomart.
Around (approximately 65%) of the line is electrified in three separate sections: one section at 1500 V DC between Wellington and Waikanae, and two sections at 25 kV AC: between Palmerston North and Te Rapa (Hamilton) and between Papakura and Auckland Britomart.
The first section of what became the NIMT opened in 1873 in Auckland. Construction at the Wellington end began in 1885. The line was completed in 1908 and was fully operational by 1909. It is credited for having been an economic lifeline, and for having opened up the centre of the North Island to European settlement and investment. In the early days, a passenger journey between Wellington and Auckland could take more than 20 hours; today, it takes approximately 11 hours.
The NIMT has been described as an "engineering miracle", with numerous engineering feats such as viaducts, tunnels and a spiral built to overcome large elevation differences with grades suitable for steam engines, the ruling gradient being 1 in 50.
History
Construction
When the first sections of the NIMT were built, there was great uncertainty as to even the route in Waikato, with Cambridge, Kihikihi, Te Awamutu and Alexandra considered as possible destinations in Waikato. The central section was gradually extended to meet up in 1909, 23 years after the last of the northern and southern sections of NIMT had been opened.
Auckland to Te Awamutu
Auckland's first railway was the line between Point Britomart and Onehunga via Penrose, opened in 1873. It was built by Brogdens, as was the rest of the Auckland & Mercer Railway, for £166,000 for the to Mercer. The section from Penrose to Onehunga is now called the Onehunga Branch. The line was later continued south from Penrose into the Waikato. To support the Invasion of the Waikato, a tramway was built from Maungatāwhiri to Meremere in 1864, with a first sod event near Koheroa on Tuesday, 29 March 1864 by Auckland's Chief Superintendent of Roads & Bridges, W R Collett. Turning of the first sod of the Auckland and Drury Railway took place in 1865, a year after the last major battle. This line reached Mercer by 20 May 1875, with from Ngāruawāhia 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 railhead. There were also 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 government and merged with the New Zealand Railways Department in 1908.
The Longburn to Marton section had been opened on 18 April 1878, as part of the line linking the ports of Foxton and Whanganui.
Central North Island
In 1882, the Whitaker Ministry passed the North Island Main Trunk Railway Loan Act, to expedite construction of the North Island Main Trunk south of Te Awamutu by authorising the overseas borrowing of a million pounds (probably in London) for the work. From Te Awamutu, it was proposed that the line be built via Taupo or via Taumarunui, the eventual route. Four options were considered before the Minister of Public Works decided on the present route in 1884, but, when it was realised just how difficult that route was, further surveys considered two other options in 1888.
Construction of the final central section began on 15 April 1885, when paramount chief Wahanui of Ngāti Maniapoto turned the first sod outside 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 nine viaducts and the world-famous Raurimu Spiral.