Construction yard at entrance to the Otira tunnelThe Midland line of the New Zealand railways network connects Christchurch on the east coast of the South Island to the West Coast. Confronting many geographic obstacles, the line must traverse the Southern Alps. At Arthur's Pass, a tunnel through the Southern Alps to Otira had to be constructed.
When it was completed in 1923, the Otira tunnel was the longest in the British Empire. Since the dominant railway locomotive technology at the time - steam - was impractical to haul trains through the tunnel, electric locomotives were tasked with hauling trains through the tunnel with steam resuming once again after the trip through the tunnel.
Electric locomotive at Otira
Rail service provided faster and more reliable transport for passengers and supplies to the West Coast, treacherous bars at the mouth of river harbours of Hokitika, Greymouth, and Westport putting shipping at great risk. The West Coast's major products, coal and timber, were more cheaply railed to Canterbury for domestic use and for export from the Port of Lyttelton.