KiwiRail Predecessor NZR Completes Electrification of the Otira Tunnel Section

The Otira Tunnel, piercing the Southern Alps on New Zealand’s Midland Line, has posed operational challenges since its opening in 1923. Long, steep, and poorly ventilated, the tunnel relied on electric traction to avoid smoke accumulation. By the 1980s, the original 1.5 kV DC electrification system and locomotives were outdated. On December 29, 1985, New Zealand Railways completed a major modernization: upgrading traction power systems, replacing overhead wiring, and introducing more powerful locomotives suited for steep mountain grades. Although electrification would later be removed in 1997 with the adoption of specialized diesel locomotives equipped for tunnel ventilation constraints, the 1985 upgrade ensured safe and reliable operations during a period of increasing freight traffic. The project remains an important part of New Zealand’s rail engineering history, reflecting the unique challenges posed by trans-alpine transport.