Auckland’s central rail tunnel project was accorded a preferred route last month. However, a business case has yet to be made for construction funding.

The more than NZD 1bn (USD 708.8M) tunnel’s plan will see it run between Britomart and Mt Eden.

A NZD 5M (USD 3.5M) investigation study for KiwiRail and the Auckland Regional Transport Authority identified a 3km route including locations for three new underground stations. The route will rise to a height of 70m.

Consultants narrowed down the route from three short-listed options described to the Auckland Regional Council in February.

KiwiRail chairman Jim Bolger said the preferred route required fewer curves than the other options, meaning lower costs for a boring machine and better operational speeds offering greater fuel economy for electric trains.

The route has the added advantage of running beneath public roads rather than private property for 2.4km.

Transport Authority planning chief Peter Clark said an estimated cost range of NZD 1bn (USD 708.8M) to NZD 1.5bn (USD 1bn) had yet to be narrowed as part of a business case to be developing in association with concept design work over the rest of this year, before KiwiRail decides whether to seek a notice of requirement to protect the route.