View source for Raurimu Spiral

{{Short description|Section of North Island Main Trunk}}
{{Use New Zealand English|date=April 2024}}
{{Use dmy dates|date=June 2024}}
{{Location map
 |New Zealand
 |label=Raurimu Spiral
 |lat_dir=S | lat_deg=39 | lat_min=7.4
 |lon_dir=E | lon_deg=175 | lon_min=23.8
 |position=left
 |float=right
 |caption=Location of the Raurimu Spiral in the central North Island of New Zealand.
}}
{{Raurimu Spiral}}
The '''Raurimu Spiral''', {{langx|mi|Te [[Koru]] o Raurimu}} is a single-track [[Spiral (railway)|railway spiral]], starting with a [[Horseshoe curve (transportation)|horseshoe curve]], overcoming a {{convert|139|m|adj=on}} height difference, in the central [[North Island]] of [[New Zealand]], on the [[North Island Main Trunk]] railway (NIMT) between [[Wellington]] and [[Auckland]].  It is a notable feat of [[civil engineering]], having been called an "engineering masterpiece."<ref name="HERALD">{{cite news |url=http://www.nzherald.co.nz/transport/news/article.cfm?c_id=97&objectid=10526022 |title=Steel backbone an economic lifeline |author=Dearnaley, Mathew |date=9 August 2008 |work=[[The New Zealand Herald]] |accessdate=4 November 2011}}</ref> The [[Institute of Professional Engineers of New Zealand]] has designated the spiral as a significant engineering heritage site.<ref>[http://www.ipenz.org.nz/heritage/itemdetail.cfm?itemid=2173 IPENZ]</ref>
[[File:Raurimu Railway Spiral from Helicopter - panoramio.jpg|thumb|View of the spiral from a helicopter]]
[[File:Raurimu rail stop.jpg|thumb|Raurimu railway station]]

== Background ==
During the construction of the central section of the North Island Main Trunk, a major obstacle arose: how to cross the steep slopes between the [[North Island Volcanic Plateau]] to the east and the valleys and [[gorge]]s of the [[Whanganui River]] to the west?
[[File:Raurimu Spiral map.png|right|thumb|Map of the spiral, from [[OpenStreetMap]]]]

South of [[Taumarunui]], the [[terrain]] is steep, but not unmanageable, with the exception of the stretch between [[Raurimu]] and [[National Park, New Zealand|National Park]], where the land rises too steeply for a direct rail route. A direct line between these two points would rise {{convert|200|m}} in a distance of some {{convert|5|km}}, a [[Grade (slope)|gradient]] of 1 in 24.  The area was thoroughly surveyed during the 1880s in an attempt to find a route with a lesser grade, but the only viable possibility seemed to require a {{convert|20|km|adj=on}} detour and nine massive viaducts. Even then, the gradient would've been steeper than 1 in 50.{{sfn|Christie|1975|p=312}}

== Construction ==
The problem was solved in 1898 by a surveyor in the employ of [[Robert Holmes (engineer)|Robert Holmes]], [[New Zealand Ministry of Works|Public Works Department]] engineer. He proposed a line that looped back upon itself and then spiralled around with the aid of tunnels and bridges, rising at a gradient of 1 in 52. Though costly and labour-intensive, the scheme was still cheaper than the previous plan by Browne and Turner which required 9 viaducts down the Piopiotea River. The most remarkable feature is that there is no place to view the complete line. By all accounts, Holmes visualised the layout in his imagination.{{sfn|Christie|1975|p=314}}

The railway forms an ascending spiral southwards, with two relatively short tunnels, a circle and three hairpin bends. From the north, trains pass Raurimu station before going round a 200° bend to the left in a [[Horseshoe curve (transportation)|horseshoe curve]], climbing above the track on which they have just travelled. Two sharp bends to the right follow, after which the line passes through two short tunnels, the Lower Spiral Tunnel (384 m) and the Upper Spiral Tunnel (96 m). Trains then complete a full circle, crossing over the Lower Spiral Tunnel through which they have just passed which is {{convert|23|m|adj=on}} below, before continuing towards Wellington. {{convert|2|km|spell=In}} further on the line has two more sharp bends, to the right and then to the left.

After the second of these bends a train has risen {{convert|132|m}} and travelled {{convert|6.8|km}} from [[Raurimu railway station|Raurimu]]– the straight-line distance is {{convert|2|km}}. Some of the sharp curves are only 7½ chains (150 m) radius.

Although [[spiral (railway)|spirals]] are relatively common in the [[Alps]], particularly in [[Switzerland]], they generally involve extensive tunnelling inside mountainsides. A masterly feature of Holmes' layout is the way in which it uses natural land contours so that no viaducts are needed, and only two short tunnels.

==Folklore==
Legend has it that a locomotive engineer once engaged the emergency brakes of his train upon mistaking the light of his own [[Brake van|guard's van]] on a nearby part of the spiral for the rear of a different train directly ahead of him.{{sfn|Pierre|1981|p=97}}<ref name=JOURNEYCOUNTS>{{cite news|title=Auckland to Wellington: It's the journey that counts|url=http://www.nzherald.co.nz/auckland-region/news/article.cfm?l_id=117&objectid=10734806|accessdate=28 June 2011|newspaper=[[The New Zealand Herald]]|date=28 June 2011|first=Danielle|last=Wright}}</ref>

== See also ==
* [[North Island Main Trunk]]
* [[Raurimu railway station]]
* [[Spiral (railway)]]
* [[Tehachapi Loop]]

==References==
===Citations===
{{Reflist}}

===Bibliography===
{{refbegin}}
*{{cite book|title=North Island Main Trunk: An Illustrated History|first=Bill|last=Pierre|year=1981|publisher=Reed|location =Wellington|isbn=0-589-01316-5|pages=Chapters 12 & 13, pages 42–49 |url=https://www.google.com/books/edition/North_Island_Main_Trunk/yywSAQAAMAAJ}} (limited online search only)
*{{cite book |title=By Design: A brief history of the Public Works Department Ministry of Works 1870–1970 |last=Noonan |first=Rosslyn J. |year=1975 |url=https://archive.org/details/by-design-1975|contribution=Appendix XIV, The Raurimu Spiral |contributor-last=Christie |contributor-first=J. H. |pages=312–315 }}
{{refend}}

== External links ==
{{commons category}}
*[https://paperspast.natlib.govt.nz/parliamentary/appendix-to-the-journals-of-the-house-of-representatives/1906/II/1544 1906 photo of cutting being excavated at what was then known as Pukerimu]
*[http://www.ipenz.org.nz/heritage/itemdetail.cfm?itemid=71 NZ Engineering Heritage North Island Main Trunk line page]
*[http://www.nzhistory.net.nz/media/photo/raurimu-spiral ''Raurimu Spiral'' (NZR Publicity pamphlet)]
*{{NZHPT|7588|Raurimu Spiral}}
*The New Zealand Railways Magazine, Volume 11, Issue 6 (1 September 1936) [https://nzetc.victoria.ac.nz/tm/scholarly/tei-Gov11_06Rail-t1-body-d12.html digitised at NZETC]
*{{cite web|url= https://railsoc.org.nz/ms3/ |title= Two locomotives and train descending the Spiral, 1995 |publisher= NZRLS |date= 1995 }}

{{coord|39|7.4|S|175|23.8|E|region:NZ-WGN_type:landmark|display=title}}

[[Category:Buildings and structures in Manawatū-Whanganui]]
[[Category:Heritage New Zealand Category 1 historic places in Manawatū-Whanganui]]
[[Category:Rail transport in Manawatū-Whanganui]]
[[Category:Ruapehu District]]
[[Category:Railway attractions in New Zealand]]
[[Category:Rail infrastructure in New Zealand]]