Ōtira rail tunnel opened

4 August 1923

The 8.5-km Ōtira tunnel, which pierced the Southern Alps and linked Christchurch with Greymouth, was formally opened by Prime Minister William Massey. At the time it was the longest tunnel in the southern hemisphere and the British Empire, and the sixth-longest in the world.

Work on the transalpine (or ‘Midland’) line had begun as long ago as 1887. This ambitious private project, launched by the New Zealand Midland Railway Company, aimed to connect the West Coast with both Canterbury and Nelson. Progress was painfully slow and in 1895 the project was taken over by the government’s Public Works Department (PWD), triggering legal disputes and further delays. The West Coast section reached Ōtira by 1900 and tenders for a long tunnel through the Alps to Arthurs Pass, 737 m above sea level, were called in 1907.

Contractor J.H. McLean & Sons began work the following year, but the project was plagued by engineering problems, extreme weather and labour shortages, and the company eventually collapsed. In 1912 the PWD took over but work slowed during the First World War. When the two ends of the tunnel were joined in 1918 the surveyors’ centre lines were found to be less than 30 mm apart, an impressive level of accuracy for the era. The line was finally opened for traffic in 1923 – 36 years after work had begun.

Due to its length and continuous steep gradient (1 in 33), it was decided to electrify the tunnel using a 1500V DC overhead system. Electric power was supplied from a small coal-fired station near Ōtira and later by hydroelectricity. The tunnel section of the line was initially served by five English Electric Eo-class locomotives, which were replaced in 1968 by Toshiba Ea-class (later called EO-class) locos. The tunnel’s electric system was decommissioned in 1997 in favour of diesel power, with the locomotives' fumes being dealt with by a system of doors and exhaust fans.

From the 1920s to the 1960s popular Sunday excursions were run from Christchurch to Arthurs Pass and Ōtira. Today, the tunnel is heavily used by freight trains carrying West Coast coal to Lyttelton for export, and by the TranzAlpine tourist train.

Image: Ōtira tunnel opening

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