The most direct rail route was via the Roxburgh Branch line to its terminus at Roxburgh. However this line had an uncompensated 1 in 41 grades and five chain (100.6 metre) curves that would limit the loads to 180 tons per engine. As well, four tunnels including those at Manuka and Round Hill on the line restricted the physical size of what could be transported, leading to consideration being given to enlarging them. This would have been expensive and restricted use of the line while it was being undertaken. As an alternative an investigation was undertaken into lengthening the Tapanui Branch line from its terminus at Edievale though a tunnel and some clay cuttings in the Dunrobin Hills to the Clutha River where it could connect with the Roxburgh branch line. Eventually it was decided to wherever possible use the Roxburgh branch line for all construction materials and smaller items of equipment. These were transported on the Main South Line to Milton where they transferred to the Roxburgh Branch which conveyed them to Roxburgh and from there transported by road to the power station. Consideration was given to extending the line to the construction site but this wasn't proceeded with due to the difficulty of getting past the east end of the existing Roxburgh suspension bridge. To improve the line's carrying capacity some curve easements were undertaken near Round Hill.