Auckland Transport is considering adding two more trains to its order for a 57-strong electric fleet from Spain, for a $113 million extension of rail electrification, from Papakura to Pukekohe.
The council-controlled organisation estimates that patronage growth - from a sector picked to more than treble its population by 2041 to almost 80,000 residents - would offer an economic pay-off of $2.10 for each dollar invested.
That would depend on building new stations with park-and-ride facilities at Drury and at Paerata, to the north of Pukekohe, to coax commuters from their cars.
Simply extending electrification to Pukekohe without the intermediate stations would provide a return of just 90c for each dollar invested, according to an Auckland Transport staff report to its board.
The project has come under consideration at an advanced stage of the Government's $500 million electrification of Auckland's rail network from Britomart to Pukekohe and Swanson, which is due to be complete by August.
Upgrades to Papakura and Pukekohe stations have already been provided for in Auckland Transport's long-term budget at a cost of $18.6 million, leaving $83.6 million to be found from elsewhere.
Staff have been asked to report back to their board early next year on possible funding options.