Previously trains were restricted to a maximum weight of 1100 or 1400 tonnes with a banking locomotive to cope with the severe gradients south of Picton, and this meant southbound freight trains had to be split into two, significantly increasing transit times.

The rebuilding of the train ferry Aratere last year substantially increased railfreight capacity across the Cook Straight, creating a bottleneck at Picton. KiwiRail has now responded by increasing trains to 1600 tonnes through the introduction of new wagons with heavier drawgear and the deployment of additional higher-powered locomotives to the South Island.