The Otira Tunnel is a railway tunnel on the Midland Line in the

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

of New Zealand, between

Otira Otira is a small township fifteen kilometres north of Arthur's Pass in the central South Island of New Zealand. It is on the northern approach to the pass, a saddle between the Otira and Bealey Rivers high in the Southern Alps. A possible meani ...

and

Arthur's Pass Arthur's Pass, previously called Camping Flat then Bealey Flats, and for some time officially Arthurs Pass, is a township in the Southern Alps of the South Island of New Zealand, located in the Selwyn district. It is a popular base for explorin ...

. It runs under the

Southern Alps The Southern Alps (; officially Southern Alps / Kā Tiritiri o te Moana) is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the range's western side. The name "Southern ...

from Arthur's Pass to Otira – a length of over . The gradient is mainly 1 in 33, and the Otira end of the tunnel is over lower than the Arthur's Pass end.

Construction

Construction commenced in 1907 and a "breakthrough" celebration was held on 21 August 1918 by the Minister of Public Works Sir William Fraser. When the tunnel opened on 4 August 1923, it was the seventh longest tunnel in the world and the longest in the

British Empire The British Empire was composed of the dominions, colonies, protectorates, mandates, and other territories ruled or administered by the United Kingdom and its predecessor states. It began with the overseas possessions and trading posts esta ...

. The Midland Railway Company investigated alternatives to a long tunnel, but a line over the pass with gradients of 1 in 50 on both sides was not practical. Other options for a line over the pass were a cable-hauled system or a line of 1 in 15 gradient using either the Fell system or a

rack railway A rack railway (also rack-and-pinion railway, cog railway, or cogwheel railway) is a steep grade railway with a toothed rack rail, usually between the running rails. The trains are fitted with one or more cog wheels or pinions that mesh with ...

using the Abt system (or even an S-shaped tunnel under Mount Rolleston). However, the government did not favour the Fell system as used on the

Rimutaka Incline The Rimutaka Incline was a , gauge railway line on an average grade of 1-in-15 using the Fell system between Summit and Cross Creek stations on the Wairarapa side of the original Wairarapa Line in the Wairarapa district of New Zealand. The t ...

which was expensive to operate. After taking over the line the government decided in 1900 on a 10 km long straight tunnel with a gradient of 1 in 37, but after expert advice opted two years later for an 8.55 km tunnel at the slightly steeper gradient of 1 in 33. A contract to build the tunnel in five years was let to the engineering firm of John McLean and Sons who started at the Otira end in 1908, using the "drill and blast" method. With progress difficult and slow McLeans asked to be relieved from the contract in 1912, and were financially ruined (the tunnel cost over twice the contract price of £599,794 ($1,200,000). The government could find no other tenderers, so the work was taken over by the

Public Works Department This list indicates government departments in various countries dedicated to public works or infrastructure. See also * Public works * Ministry or Board of Public Works, the imperial Chinese ministry overseeing public projects from the Tang ...

. The government considered halting construction in World War I, but the Imperial Government requested that work should continue in case the German navy blockaded the West Coast ports used for coal shipment. The breakthrough was on 20 July 1918, but concrete lining took a further three years, and then two more years before the tunnel opened. There were eight fatalities during construction. Its opening was marked by the

British and Intercolonial Exhibition The British and Intercolonial Exhibition was a small world's fair held between 15 December 1923 and 2 February 1924 in Hokitika, West Coast, New Zealand to mark the opening of the Otira Tunnel and the diamond jubilee of Westland Province. The pa ...

Electrification

TranzAlpine and Otira Tunnel from Albert's Pass station

The tunnel dimensions were high and wide at rail level, increasing to at the widest point. Because of its length and gradient, gases such as

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

and

carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...

could easily build up, potentially making the tunnel both unhealthy for the train's occupants and unworkable with steam engines. Thus, the tunnel was

electrified Electrification is the process of powering by electricity and, in many contexts, the introduction of such power by changing over from an earlier power source. The broad meaning of the term, such as in the history of technology, economic history ...

with a 1500 V DC overhead system. A small

coal-fired power station A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts Nameplate capacity, capacity. They ...

was built near Otira to provide

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...

until 1941 when it was replaced by a connection to the national grid. The locomotives used were the EO class, then from 1968 the EA class. In 1988, trials began using DX class locomotives instead of electric locomotives. While the trials were unsuccessful, it was found in trials held in 1991 that upgrading the DX locomotives with new air intakes and putting extraction fans on the Otira end of the tunnel could allow for the replacement of the electrification. Because of the increasing age of the electrification and the availability of upgraded DX class diesel locomotives, the electrification was decommissioned in 1997 and the equipment removed. This marked the end of electrification in the South Island. To overcome the fume problem, a combination of a door and fans are used, similar to that used in the

Cascade Tunnel The Cascade Tunnel refers to two railroad tunnels (original and its replacement) in the northwest United States, east of the Seattle metropolitan area in the Cascade Range of Washington, at Stevens Pass. It is approximately east of Everett, wit ...

in the United States of America, which was also once electrified. After a train enters the tunnel from the Otira end the door closes off the entrance, and a large fan extracts the fumes behind the train. Once the fumes have been extracted, the door is reopened. Because of the fumes, the

TranzAlpine The TranzAlpine is a passenger train operated by The Great Journeys of New Zealand in the South Island of New Zealand over the Midland Line; often regarded to be one of the world's great train journeys for the scenery through which it passes ...

observation car An observation car/carriage/coach (in US English, often abbreviated to simply observation or obs) is a type of railroad passenger car, generally operated in a passenger train as the rearmost carriage, with windows or a platform on the rear of th ...

s are closed for the trip through the tunnel.

References

External links

Otira steam power station, 1928

* , illustrated description of the construction and opening of the Otira Tunnel * * * * Westland District Railway tunnels in New Zealand Tunnels completed in 1923 Rail transport in the West Coast, New Zealand Rail transport in Canterbury, New Zealand Transport buildings and structures in Canterbury, New Zealand Transport buildings and structures in the West Coast, New Zealand

Construction

Electrification

References

Further reading

External links