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
Track 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 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 Midland Railway Company investigated options 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 using the Abt system (or even a S-shaped tunnel under Mount Rolleston). However the government did not favour the Fell system as used on the Rimutaka Incline 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 5 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. 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. 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.