Auckland looks set to get a new fleet of battery-powered trains by 2019.
The 17 hybrid trains would run off either electricity or high-tech batteries that could carry them to Pukekohe, beyond the existing electrified network.
The city's transport agency has backed the $207 million purchase, which still needs funding from both Auckland Council and the government.
The fleet would be added to the 57 electric trains which have been in service for more than two years, but which the agency said would be at capacity in two years' time.
Mayor Phil Goff said the new trains needed to be bought now to meet greater than estimated demand for rail travel.
"Demand has increased by 17 percent over the last year and within months will achieve a record 20 million passenger trips a year in Auckland," Mr Goff said.
"The result is a more attractive public transport system which will help tackle growing congestion levels, especially on the Southern Motorway.
"The units could ultimately be transferred to the Kumeu-Huapai line when the Southern line is electrified in 2025."
Auckland Transport has been studying the battery-power option for more than a year and described it as cutting-edge technology.