Tranz Alpine Roaming around the Christchurch Rails

The Tranz Alpine is one of the three passenger services offered by Great Journeys of New Zealand, and runs a day return service between Christchurch and Greymouth. The journey between Christchurch and Greymouth is one of the most scenic journeys available in New Zealand, and includes the Otira Tunnel, which is the longest passenger tunnel in New Zealand.
For the 15 minute journey through the Otira Tunnel, another two locomotives are added to the front, and another two are added on the rear of the train. These extra locomotives are called bankers, and are necessary in case a emergency occurs in the tunnel, and the train can return to the closest exit.