150 Railway Tunnels Built to Traverse New Zealand's Mountainous Terrain
In 1921 the Otira tunnel pierced the Southern Alps making it the longest tunnel in the British Empire and southern hemisphere (8.56 km long)
The topography of New Zealand made the construction of railways a major engineering problem, not least the need for 150 tunnels in the hilly to mountainous terrain of so much of the country.
New Zealand's greatest achievement was piercing the Southern Alps with the Otira Tunnel in 1921 with a tunnel 8.56 kilometres long, at that time the longest in the British Empire and in the Southern Hemisphere. It was opened in 1923, using electric locomotives. The longest freight tunnel in New Zealand is the Kaimai tunnel (8.79 km) and the longest passenger tunnel is the Rimutaka tunnel (8.798 km).
For obvious reasons tunnels do not have the visual impact of railway bridges. Today, with some abandoned tunnels converted to public walkways (eg Karangahake, Chasm Creek, Kawatiri), many people now experience them as exciting structures.
1861-67 : Lyttelton Tunnel (2.6 km)
The first essay was the Lyttelton tunnel through the Port Hills to give access to Christchurch. Begun in 1861, it was an ambitious project for the 11-year-old Canterbury settlement. Drilling through the hard volcanic rock for 2.6 kilometres saw the mostly unlined tunnel completed in December 1867.
19??-23 : Main Trunk Lines in North Island (26 tunnels) and South Island (?? tunnels)
The main tunnelling challenge came with the construction of the Main Trunk lines in both islands and of the Midland Line. The North Island Main Trunk had 26 tunnels totalling 12 kilometres in length, with such names as Mataroa or Pit, Hedgehog, and Elk or Utiku. Many of these were driven through unstable country in remote areas and entailed all manner of difficulties for engineers and tunnellers. The Southern Alps were pierced with the Otira Tunnel in 1921 with a tunnel 8.56 kilometres long.
Construction Method and Materials : from Hand-Tools to Giant Boring Machines
Some early tunnels were mainly unlined, relying on the hard native rock as in the Lyttelton tunnel. Generally they were lined with brick, the traditional material, but in 1893 the first use of concrete was carried out as block lining in Kohatu Tunnel through the Spooner Range on the Nelson-Kawatiri line. Later, concrete was poured in-situ and this is the practice today. In some instances brick, stone and concrete have all been used in the one tunnel, as in the Poolburn Gorge tunnels on the Otago Central line.
From the 1860s the usual method of construction was to drive in two headings, an upper and a lower in the horseshoe profile, with timbering for support. In the late 1930s the Bartletts-Waikokopu section of the Napier-Gisborne line saw the first use in New Zealand of the 'American' system, with a semi-circular top and vertical sides, enabling the whole face of the tunnel to be attacked at once, and allowing maximum operating room for the workmen. The timbering was arched and mechanical scrapers were used to speed excavation and loading of spoil. Steel-lined formwork for the pumped concrete followed. In the Kaimai Tunnel on the East Coast Main Trunk, completed in 1978, modern technology was used in the form of a giant boring machine.
Longest Bored Tunnels
From longest to shortest.
Kaimai - 8879 m - opened 12 September 1978 - near Apata on the East Coast Main Trunk Railway Line to Tauranga, the longest rail tunnel in New Zealand.
Rimutaka - 8798 m - opened 3 November 1955 - between Upper Hutt (Wellington) and Featherston (Wairarapa), replaced the Rimutaka Incline, a Fell mountain railway, the longest tunnel in New Zealand that carries regular passenger trains.
Otira - 8566 m - opened 1923 - between Arthur's Pass and Otira, in the Southern Alps on the transalpine Midland line - continuous 1 in 33 grade - electrified until 1997.
Tawa No 2 – 4324 m - opened 1935, goods on one line, 1937 all traffic - longest double-track tunnel in New Zealand. Between Ngauranga (Wellington) and Glenside (Tawa). With the Tawa No 1 Tunnel (1238 m), part of the Tawa Flat deviation.
Tikiwhata - 2989 m - opened 1943, between Wairoa and Gisborne.
Lyttelton - 2596 m - opened 1867-12-09, between Heathcote Valley (Christchurch) and Lyttelton.
Turakina - 2091 m - opened 1947, between Marton, New Zealand and Wanganui.
Shortest Bored Tunnels
A 39.83 m long tunnel - opened 1906, between Staircase and Avoca, Midland Line.
A 42.05 m long tunnel - opened 1891, near Woodville, in the Manawatu Gorge. - was daylighted in 2008
An EF electric locomotive on the North Island Main Trunk line, 2006
Other rail tunnels
Purewa Tunnel, a 800m tunnel on the Eastern Line in Auckland
Disused rail tunnels, North Island
Cruickshanks - opened 1 January 1878, between Mangaroa and Upper Hutt. Public access uncertain (see Valley Signals site for information)
Mangaroa - 152 m - opened 1 January 1878, at Tunnel Gully recreation area, Te Marua, Upper Hutt. Now a walkway.
Summit - 584 m, and three shorter tunnels, opened 12 October 1878 on the Rimutaka Incline. On the Rimutaka Rail Trail.
Okaihau - on the never-opened extension of the Okaihau Branch to Rangiahua, unused but can be walked through - easily spotted from SH1 passing Okaihau township.
Parnell Tunnel - single track, on the Auckland - Newmarket Line, adjacent to the current double-track tunnel. Closed, with no public access.
Karangahake - 1006 m, in the Karangahake Gorge, on the former East Coast Main Trunk, closed in 1978. Now a walkway.
Porootarao - 1071 m, replaced by new tunnel on deviation in 1980.
No.8 tunnel bypassed in 1985 by the Mangaonoho Deviation of the North Island Main Trunk.
No.19 tunnel daylighted in 1972, on the section of line bypassed in 1985 by the Mangaonoho Deviation of the North Island Main Trunk.
No.15 tunnel bypassed in 1987 by the Ohakune-Horopito deviation of the North Island Main Trunk. Accessible from one end only.
No.11 tunnel south of Taihape bypassed in 1985 by a deviation of the North Island Main Trunk.
No.12 (Hedgehog) tunnel north of Taihape bypassed in 1985 by a deviation of the North Island Main Trunk. Adjacent to State Highway 1.
No.10A, 10B, 10C, 10D, 10E, 10F tunnels bypassed in 1981 by the Mangaweka Deviation of the North Island Main Trunk. All are on private land.
No.9 tunnel bypassed at the west end of the Makohine Viaduct in 1984, on the North Island Main Trunk.
Four tunnels on the closed Moutohora Branch, ranging from 45 to 258 m long. One tunnel is accessible on a public walkway, the others can be viewed from public roads.
Historically one or more tunnels may have been built on the closed Ngatapa Branch but no trace exists today.
No 24 tunnel on the Palmerston North - Gisborne line - 123 m long (collapsed).
No 12 tunnel on the Wellington & Manawatu Railway (now Kapiti section of NIMT) between Paekakariki and Paraparaumu - abandoned in 1900.
No. 3, 4 and 5 tunnels on the Palmerston North Gisborne line were daylighted in 2007.
No.4 (Kai Iwi) tunnel on the Marton New Plymouth Line was bypassed in 2008.
Disused rail tunnels, South Island
Hunts Road - former Catlins River Branch, 221 m long. Public walkway access. This was the southernmost tunnel in New Zealand.
Glenham Branch, 301 m long. Possible public access. The second most southerly tunnel.
Spooners Range Tunnel - 308 m long, on the closed Nelson Section. Accessible by public walkway.
Kawatiri Tunnel - 185 m long, on the closed Nelson Section. Accessible by public walkway.
No 4 Tunnel - south of Oaro township on the Main North Line. Access on foot south of township via a railway bridge.
Chasm Creek - former Seddonville Branch. Accessible by public walkway.
Charming Creek - former private coal railway. Accessible by public walkway.
Former coal tramways at Stockton and Denniston. Public access.
Cape Foulwind - former quarry line. Public access but tunnel has largely collapsed.
Rewanui Incline - two short tunnels now used by access road.
Puketeraki - 157 m long. Line deviated around in a cutting. Partly collapsed and ends have been fenced over. Abandoned about 1936 
Sawyers Bay, Dunedin - 101 m long, line deviated through new tunnel. Status unknown. Appears to have been filled in at entrances.
Caversham, Tunnel History Dunedin - 865 m long, line deviated through new double-track tunnel. Public access to both ends but it is quite muddy. The access down the steps between intersections with Ensor Street and Townleys Road has been fenced off, but easy to get under, on the opposite side of the road to the Caversham entrance of the current tunnel).
Chain Hills (Wingatui) - 158 m long, line deviated through new double-track tunnel.Tunnel Images Tunnel gated shut both ends and on private land.
Three tunnels on the Otago Central Rail Trail (former Otago Central Railway), ranging in length from 152 to 229 m. All have public access.
Three tunnels on the former Roxburgh Branch ranging from 226 to 443 m. Tunnel No 1 is in public reserve, appears to be no access to others.
Rakis and Tapui Tunnels on the former Tokarahi Branch. Can be seen from roads, on private land.
Conical Hill - 71 m long, on the former Tapanui Branch. Public access through walkway.
Tunnel Hill Historic Reserve - between Balclutha to Owaka, 200 m long, public access through walkway.
No.22 Tunnel on the Main North Line. Daylighted in 1981.
No.23 Tunnel on the Main North Line. Daylighted in 1979.