Otira Tunnel

Otira Tunnel

Otira Tunnel during construction, ca 1910
Overview
Line	Midland Line
Location	Southern Alps, South Island, New Zealand
Coordinates	North (West coast) portal: 42°51′45″S 171°32′55″E / 42.8625°S 171.5487°E / -42.8625; 171.5487 East (Canterbury) portal: 42°56′21″S 171°33′47″E / 42.9392°S 171.5630°E / -42.9392; 171.5630
Start	Otira, West Coast
End	Arthur's Pass Canterbury
Operation
Opened	4 August 1923
Owner	ONTRACK
Operator	KiwiRail, Tranz Scenic
Character	Single bore rail tunnel
Technical
Line length	8566 m
Gauge	1067 mm (3' 6")

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 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 cars are closed for the trip through the tunnel.^[1]

References

1. ^ Gibson, Anne (20 January 2007). "Cross-country call of the whitebait". The New Zealand Herald. http://www.nzherald.co.nz/new-zealand-travel/news/article.cfm?c_id=1500882&objectid=10419000. Retrieved 1 November 2011. 

External links

• Tunnel opening; engineering heritage
• Otira steam power station, 1928
• Photo of Power House, Otira
• View of the Power House and Otira
• View approaching Otira at 40 mph
• Inside Compressor House used during construction
• View of Colour Light signals Otira, 1926