North Island Main Trunk Line

Category
Engineering Work (eg road, bridge, sawmill, dam)

Description
Opened in 1908, the NIMT linked Auckland with Wellington, Taranaki
and Wanganui, and contributed to the development of the Central
North Island.

Made possible by pioneering engineering amid the challenges of a frontier land, and lately enhanced by modern technology, the North Island Main Trunk Railway is New Zealand’s most significant land route.

From 15 April 1885 when Maniopoto paramount chief, Wahanui turned the first sod of the Main Trunk railway project near Te Awamutu, and Premier Robert Stout wheeled this away, it took 23 years to complete the line. Another Premier, Sir Joseph Ward, drove the last spike on 6 November 1908. A through train service began three days later.

Most of the construction work had to be carried out by hand. Oxen, horses and small steam locomotives assisted with the bulk movement of materials. It was only in the last two years that one of New Zealand’s first steam shovels was brought in to help dig the cuttings. That was the start of a mechanical age in earthworks for this country.

The line traversed some extremely challenging terrain, which posed many problems for the engineers locating the route. The diagram shows the grades between Te Kuiti and Marton and gives an indication of the problems encountered.

The location of the Raurimu spiral about 1898 by R W Holmes was the key to a workable climb from Taumarunui to the National Park summit. At that time detailed location of the final line was still a field engineer’s decision. The required 132 m rise over a distance of 2 km in a direct line was achieved by the use of the famed ‘Spiral’ loop and horseshoe curves using the topography very skilfully to minimise cut, fill and tunnelling.

The bridgeworks designed by the Public Works Department and built by the Public Works Department and engineering firms such as Andersons Ltd of Christchurch, were to the best standards of the day and were surprisingly modern. The Mangaweka Viaduct (now demolished) was typical of many of the major structures on the North Island Main Trunk. Most of these viaducts had their steelwork fabricated in the pioneering settlements such as Mangaonoho and Makatote. (There is still an Ironworks Road at Mangaonoho, although the sites of both workshops are less obvious).

Andersons’ workshop at Makatote was extremely well equipped for its time. It had electric overhead travelling cranes and the cableway used to erect the viaducts was electrically controlled as well. The design loading for bridges and viaducts was an engine of 84 tons, although the 94 ton ‘X’ Class were used from the opening of the line. Following detailed strengthening these structures have carried the 145 ton ‘K’ and ‘Ka’ locomotives, while those retained on the now electrified route carry the 106 tonne ‘30’ Class electrics of even higher axle loading than the steamers.

IPENZ “Engineering to 1990” project
This item of New Zealand’s engineering heritage was recognised as part of the IPENZ “Engineering to 1990” project which the Institution organised to help celebrate the country’s sesquicentenary in 1990. A plaque was unveiled to mark the significance of this power station as part of the development of the nation.

References:
R S Fletcher; “Single Track, The Construction of the North Island Main Trunk Railway”, Collins, Auckland, 1978.

Bill Pierre; “North Island Main Trunk, An Illustrated History”, Reed, Wellington, 1981.

F K Roberts: “A Compendium of Railway Construction, Part II, North Island Main Trunk”, New Zealand Railway & Locomotive Society, Wellington, 1990.

A L R Merrifield; “New Zealand’s North Island Main Trunk Railway: 1870-1908”, by, Proceedings of the Institution of Civil Engineers, Vol 162, Issue EH4, November 2009.

A L R Merrifield; “A Centennial Review of the North Island Main trunk Railway: Geology of the West-Central North Island and its Influence on Transport Development”, Proceedings of 3rd Australasian Engineering Heritage Conference, 2009.


Owner: NZ Railways Corporation
Design: Public Works Department
Resident engineer (south): F W Furkert
Resident engineer (north) J B Louch

Location
The North Island Main Trunk goes from Auckland to Wellington. At various stages it is adjacent to State Highway One (Auckland to Hamilton and Waiouru to Wellington). Through the central North Island (Hamilton to Waiouru) its route is similar to that of State Highway 4. The Monument celebarting the Last Spike is near the Manganui O te Ao River on State Highway 4. At Raurimu on State Higway 4, there is a viewing platform for the Raurimu Spiral.

Region/s
Auckland, King Country / Central Volcanic Plateau, Waikato, Wanganui / Manawatu, Wellington / Kapiti

Access Info
At various stages it is adjacent to State Highway One (Auckland to Hamilton and Waiouru to Wellington). Through the central North Island (Hamilton to Ohakune) its route is similar to that of State Highway 4. The Monument celebrating the Last Spike is near the Manganui O te Ao River on State Highway 4. At Raurimu on State Higway 4, there is a viewing platform for the Raurimu Spiral although this is increasingly difficult to see as trees grow near the line.

Nature of Engineering
Rail Transportation