Business Case exists – in draft form
Resident transport advocate (and researcher) Harriet Gale recently filed an Official Information Act (OIA) on where things were progressing with building the Third Main on the Southern and Eastern Lines between Otahuhu and Wiri. The purpose of the Third Main (that would eventually extend to Pukekohe) is to detangle the increasing amount of freight trains from the ever-increasing amount of passenger trains.
In short the Third (and Fourth) Main allows increases in the amount of freight and passenger trains that can traverse the Southern Line.
An extra six freight trains (using a formula of one 50x wagon train moving 100 containers) means ~300 trucks not congesting the Southern Motorway especially in the peak and shoulder-peak periods thus freight moving efficiently through a very busy area of Auckland. Detangling the trains also means more passenger trains, remembering that:
So for $53m to start stage one of the Third Main we get some serious wins on the board in moving people and freight (away from the motorways)($144m to bring the Third Main to Papakura).
According to the Auckland Transport Alignment Program (ATAP) stage one of the Third Main is a first decade project with the next two stages in decades two and three:
The Fourth Main is also mentioned.
Effectively all that we (Auckland) are waiting on is for Transport Minister Simon Bridges to present the cheque for $53m to get the Third Main started. The economic, social and environmental benefits of the Third Main would outstrip those of the $1.85b East West Link motorway/expressway.
Thanks to Harriet on the OIA (can be read here.)