Otira Tunnel
Encyclopedia
The Otira Tunnel is a railway tunnel
on the Midland Line
in the South Island
of New Zealand
between Otira
and Arthur's Pass
. It runs under the Southern Alps
from Arthur's Pass to Otira - a length of over 8.5 kilometres (5.3 mi). The gradient is mainly 1 in 33, and the Otira end of the tunnel is over 250 m (820.2 ft) lower than the Arthur's Pass end. Construction started in 1907 and it opened on 4 August 1923; at the time of its construction, it was one of the longest tunnels in the world.
Because of its length and gradient, gases such as carbon dioxide
and carbon monoxide
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
with a 1500V
DC
overhead system
. A small coal-fired power station
was built near Otira to provide electricity
. The locomotives used were the EO class
, then from 1968 the EA class
.
Because of the increasing age of the electrification and the availability of upgraded DX Class
diesel locomotives, the electrification was decomissioned 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 is used, similar to that used in the Cascade Tunnel
in the USA, 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
's observation car
s are closed for the trip through the tunnel.
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...
on the Midland Line
Midland Line, New Zealand
The Midland line is a 212 km section of railway between Rolleston and Greymouth in the South Island of New Zealand. The line features five major bridges, five viaducts and 17 tunnels, the longest of which is the Otira tunnel.-Freight services:...
in the South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
between Otira
Otira
Otira is a small township seven kilometres north of Arthur's Pass in the central South Island of New Zealand. It is on the western approach to the pass, a saddle between the Otira and Bealey Rivers high in the Southern Alps...
and Arthur's Pass
Arthur's Pass
Arthur's Pass is a mountain pass in the Southern Alps of the South Island of New Zealand. It marks part of the boundary between the West Coast and Canterbury regions, 140 km from Christchurch and 95 km from Greymouth. The pass lies in a saddle between the valleys of the Otira River, a...
. It runs under the Southern Alps
Southern Alps
The Southern Alps is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the island's western side...
from Arthur's Pass to Otira - a length of over 8.5 kilometres (5.3 mi). The gradient is mainly 1 in 33, and the Otira end of the tunnel is over 250 m (820.2 ft) lower than the Arthur's Pass end. Construction started in 1907 and it opened on 4 August 1923; at the time of its construction, it was one of the longest tunnels in the world.
Because of its length and gradient, gases such as carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
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
Railway electrification system
A railway electrification system supplies electrical energy to railway locomotives and multiple units as well as trams so that they can operate without having an on-board prime mover. There are several different electrification systems in use throughout the world...
with a 1500V
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
overhead system
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...
. A small coal-fired power station
Coal-fired power station
A coal-fired power station produces electricity, usually for public consumption, by burning coal to boil water, producing steam which drives a steam turbine which turns an electrical generator...
was built near Otira to provide electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
. The locomotives used were the EO class
NZR EO class (1923)
The New Zealand Railways EO class of 1923 were electric locomotives used on the steep Otira to Arthur's Pass section of the Midland Line. They were primarily for pulling trains through the 8.5 km Otira Tunnel to avoid the buildup of steam, smoke and soot....
, then from 1968 the EA class
NZR EA class
The NZR Ea class were used by New Zealand Railways between 1968 and 1997 on the OtiraArthur's Pass section of the Midland line in the South Island, through the Otira Tunnel...
.
Because of the increasing age of the electrification and the availability of upgraded DX Class
NZR DX class
The NZR DX class is a class of 49 Co-Co diesel-electric locomotives that currently operates on New Zealand's national railway network.Built by General Electric in Erie, Pennsylvania, United States, they were introduced to New Zealand between 1972 and 1976. The class is based on the General Electric...
diesel locomotives, the electrification was decomissioned 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 is used, similar to that used in the Cascade Tunnel
Cascade Tunnel
The Cascade Tunnel refers to two tunnels at Stevens Pass through the Cascade Mountains, approximately to the east of Everett, Washington. The first Cascade Tunnel was a 2.63-mile long single track railroad, built by the Great Northern Railway in 1900 to avoid problems caused by heavy winter...
in the USA, 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
TranzAlpine
The TranzAlpine Express is a passenger train operated by Tranz Scenic in the South Island of New Zealand. This trip is often regarded to be one of the world's great train journeys for the scenery through which it passes . The journey is one-way, taking about four and a half hours...
's observation car
Observation car
An observation car/carriage/coach is a type of railroad passenger car, generally operated in a passenger train as the last carriage, with windows on the rear of the car for passengers' viewing pleasure...
s are closed for the trip through the tunnel.