The opening of the 8.5-km Ōtira tunnel completed the long-planned transalpine railway between Christchurch and Greymouth. At the time, it was the longest tunnel in the southern hemisphere and the sixth-longest in the world.
Work had begun on the ‘Midland’ line 36 years before, but the original private developers’ grand plans soon came unstuck. The government’s Public Works Department (PWD) took over in 1895 and the West Coast section reached Ōtira by 1900. Tenders for a long tunnel through the Alps to Arthurs Pass, 737 m above sea level, were called in 1907. Contractors J.H. McLean & Sons began work the following year, but the project was plagued by engineering problems, extreme weather and labour shortages, forcing the PWD to step in again.
When the two ends of the tunnel were joined in 1918, the surveyors’ centre lines were found to be less than 30 mm apart, impressive accuracy for the era. Due to the tunnel’s length and steep gradient, electric locomotives were used to haul trains through it until 1997.