What advice, if any, has he received on the estimated cost of extending the third main line, and on the estimated cost of constructing a fourth main line, on the Auckland metro rail network?

Answer

KiwiRail and Auckland Transport estimated this activity and noted it in the KiwiRail briefing to incoming Ministers. To the best of our knowledge, this estimate has not been made public. It is a major transport project and would likely be delivered in stages (i.e. third maining can generally be achieved with little to no land acquisitions, while fourth maining would require land acquisition and therefore a greater level of planning).