Engineering New Zealand Engineering Heritage Jobhunt Foundation

Name 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 Truck 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 Truck 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) a portion of which is shown on Page 24 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 form 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.

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, Taranaki, 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 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.
Nature of Engineering    Rail Transportation