|Location||Rimutaka Ranges, Wellington, New Zealand|
|Start||Maymorn, Upper Hutt|
|Opened||3 November 1955|
|Owner||New Zealand Railways Corporation|
|Operator||KiwiRail (freight), Transdev Wellington (passenger)|
|Line length||8.798 kilometres (5.5 mi)|
|No. of tracks||Single|
|Track gauge||3 ft 6 in (1,067 mm)|
|Electrified||Provided for 1500vDC but not installed|
|Operating speed||100 km/h (62 mph)|
The tunnel, which was opened to traffic on 3 November 1955, is 8.798 kilometres (5.467 mi) long. It was the longest tunnel in New Zealand, superseding the Otira Tunnel in the South Island until the completion of the Kaimai Tunnel (8.88 km, 5.55 miles) near Tauranga in 1978. Rimutaka remains the longest tunnel in New Zealand with scheduled passenger trains.
The original route between Upper Hutt and Featherston was often the subject of criticism, even before it was built. In 1898 J. H. Dobson completed several surveys on behalf of the Public Works Department into possible alternatives. Conclusions reached in 1899 as a result of these surveys did little more than confirm previous opinions. One promising possibility was a 5-mile (8.0 km) tunnel between Mangaroa and Cross Creek, which received so much attention that it nearly became the much-sought deviation. By 1900, however, it was realised that the cost of constructing such a tunnel could not be contemplated at that time.
It was not until the 1920s that significant campaigning for a replacement again prevailed on the government. In 1921-22 a feasibility study was conducted, including distances and estimated costs. Several routes were considered, including variations on previous ideas, but nothing more was done at the time.
The new Labour government of 1936 announced its intention to proceed with the Mangaroa to Cross Creek tunnel. Detailed surveys were completed in 1938/1939, but the project was again postponed due to World War II.
After World War II it became a matter of urgency to consider a replacement. The H class locomotives were showing their age, the Incline was in bad shape, and maintenance costs were increasing. Between September 1945 and July 1947 four options were considered. It was accepted that no contour line could be the solution and that a tunnel under the Rimutaka Ranges was the only satisfactory answer. The adopted route was the shortest route, a tunnel between Mangaroa and Lucena’s Creek gully.
The first shot was fired in 1948 when the Public Works Department started the tunnel with bores of 1,054 feet (321 m) at the western end and 820 feet (250 m) at the eastern end. A contract for completing the tunnel was let to a consortium of Morrison Knudsen Inc. and Downer and Company on 7 May 1951. The work commenced at the west end in July 1951 and at the east end in August. The contract was expected to be completed in four years, but the headings met on 20 April 1954 with the concrete lining finished a month later.
New Zealand Railways took possession of the tunnel on 1 February 1955, which also included approach formations and bridge piers, at which time track laying commenced. By October 1955 the signalling and centralised traffic control equipment had been installed and all the track was laid, except for a short section near Upper Hutt where the old line crossed the new line at a higher level. All traffic on the Upper Hutt to Featherston section was suspended after the arrival of the Carterton Show Day excursion train at Upper Hutt on the evening of Saturday 29 October. Over the next three days the old formation was removed, the cutting for the new formation completed and the remainder of the track laid. On Thursday, 3 November, the new line was opened and two special trains travelled from Wellington to Speedy’s Crossing to the inauguration ceremony.
The deviation's ruling grade is 1 in 70, compensated for curvature. The tightest curve is 400 metres (20 chain) radius. The tunnel rises at 1 in 400 from the western portal to the highest point on the deviation, roughly halfway through the tunnel, and then descends to the eastern portal at 1 in 180. It has an internal height of 5.18 metres (17 ft) and a width of 4.68 metres (15 feet 4 inches); it is lined with concrete with a minimum thickness of 38 cm (15 inches) inside the face of the excavation. When the tunnel holed through on 20 April 1954 the surveying error was found to be only 44.5 mm (1.75 inches).
After its completion, a 2.74 metre (9 ft) diameter vertical ventilation shaft was driven up from a point almost halfway through the tunnel. It reaches the surface beside the Rimutaka Rail Trail near the former route's Pakuratahi Tunnel. The 117 metre (380 ft) high shaft was constructed after tests showed that the tunnel would not generate enough natural ventilation if diesel traction was used through the tunnel. Originally it had been envisaged that electric traction would be used by extending the 1500-volt DC overhead electrification beyond Upper Hutt to either Featherston or Masterton, but economic studies favoured diesel traction.
The new formation included two crossing loops; at the new Maymorn Railway Station (116 wagons) and the Rimutaka Loop (95 wagons) at the eastern portal of the tunnel. There are four bridges including a five-span 91 metres (300 ft) bridge across the Mangaroa River and two underpasses near Maoribank.
There is a tunnel of 539 metres (1767 ft) near Maoribank, but on the eastern side where two short tunnels (220 metres (11 chain) and 180 metres (9 chain)) had been proposed through a spur it was cheaper to lengthen the line by 140 metres (7 chain) and have open cuttings.
The construction of the Rimutaka Tunnel consumed:
The first locomotives to work through the tunnel were the 560 kW DG class - the tunnel was too long for steam locomotives, making the Wairarapa Line the first fully dieselised line in New Zealand. Today, DBR, DC, DFT and DX class locomotives run the route.
There have been proposals to electrify the tunnel and the Wairarapa line as far north as Masterton as an extension of the Wellington suburban electrification. The tunnel was designed to enable catenary to be installed but this has not happened, and the catenary finishes just north of Upper Hutt station. In 2007, Greater Wellington Regional Council rejected a call to electrify the tunnel, on the basis that patronage did not justify the expenditure, and that the tunnel would "have to be made bigger."
Transdev Wellington operates passenger services named the Wairarapa Connection between Wellington and Masterton via the tunnel five times a day each way Monday to Thursday, six on Friday, and twice a day each way on Saturday, Sunday, and public holidays. Excursion trains also go through the tunnel, such as railway enthusiast specials and trains to the Toast Martinborough festival. Steam-hauled excursions require diesel locomotives to provide motive power through the tunnel due to the dangers of smoke in the tunnel's lengthy and confined conditions.
The tunnel is used for freight from the Wairarapa to Wellington, notably logs from local pine forests and wood products from the Juken Nissho timber mill at Waingawa, just south of Masterton.
- Keller, 1954; p. 404
- Keller, 1954; p. 413
- Cameron 1976, pp. 308,309.
- Cameron 1976, p. 316f.
- Keller 1954, pp. 404-410.
- Keller, 1954; p. 416
- "Wairarapa rail won't go electric". Wairarapa Times-Age. 12 July 2007. Retrieved 21 December 2011.
- Anon. (1950) "The Rimutaka Incline and Deviation, New Zealand", Railway Magazine, 96 (592: August), p. 543–547
- Keller, G. P. (1954) "The Rimutaka Deviation", New Zealand Engineering, 9 (12: 15 December), p. 399–420
- Cameron, Walter Norman (1976). A Line Of Railway: The Railway Conquest of the Rimutakas. Wellington: New Zealand Railway and Locomotive Society. ISBN 0-908573-00-6.
- "Rimutaka Tunnel from the Cab (2010)". video on Youtube. 5 December 2015.