Otira-Tunnel

The Otira Tunnel is a railway tunnel in the Midland Line in the South Island of New Zealand between Otira and Arthur 's Pass. He pierces here the Southern Alps with a length of 8550 m. The slope is approximately 1:33, and the end of the tunnel at Otira is about 250 m deeper than the end of Arthur 's Pass.

Construction began on 25 May 1908 contractor was the firm of J. McLean & Sons. After the technical difficulties were still greater than foreseen, the works were discontinued in 1912 after only half of the tunnel was excavated. 1913, the work by the public sector, the Public Works Department have continued. The tunnel puncture was performed in July 1918, it was celebrated with an official ceremony on 21 August 1918. The deviation of the altitude was only 29 mm, the transverse position of only 19 mm. The expansion of the tunnel and installation of electrical installations took then until August 4, 1923, when the tunnel was put into operation. He was at that time one of the longest tunnel in the world and the longest tunnel in New Zealand, but has been replaced in the meantime in New Zealand by the Kaimai tunnel and the Rimutaka tunnel on the North Island.

Because of its length and pitch it at the time was not possible to operate the route with steam, as the hazards of the flue gases for passengers and staff would have been too large. For this reason, this section was equipped with an overhead wire with 1,500 volts DC. In Otira a coal power plant was built to produce the necessary current. For use came first electric locomotives of the series Eo, then from 1968 on the EA series.

Following the example of Otiria tunnel and the Lyttelton rail tunnel was electrified.

As the locomotives were obsolete at the end of the 1990s, the electric facilities have been removed, the traction is now taken over by diesel locomotives of the class DX.

For air conditioning of the tunnel a combination of fans and a gate was installed at the tunnel portal. After the entrance of a train in the tunnel at Otira, the gate is closed and the exhaust gases are sucked out with fans behind the train. Only then the door opens again. The observation car of the TranzAlpine are not accessible during the journey through the tunnel.