Auckland's Inner Link bus route has a new electric bus as part of its fleet.

New buses added to Auckland's commuter fleet are likely to be electric from now on.

Auckland Transport hoped up to 30 electric buses each year will join the city's fleet to soak up rising patronage and replace diesels that reach their 19-year limit.

The council-owned agency said the electrification of the current fleet of 1360 buses can be paid for out existing budget for the next few years. However, the ramp-up from 2023, when contracts with bus companies are due for renewal, might need additional funding.

Todd Niall/Stuff Auckland Transport's trial electric bus on the Inner Link route

The pace of the roll-out means additional electric buses will not reduce the carbon emissions of Auckland's fleet, but will stop them rising.

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"The priority for us will be focussing on how to improve air quality in the city centre," said Darek Koper, Auckland Transport's manager of bus services.

Supplied/Auckland Transport An artist's impression of the new CityLink electric bus, 12 of which will enter service by the end of 2020

Auckland Transport also needed to introduce more electric buses on routes that service the city centre, while shiftng existing diesel buses to meet demand elsewhere, he said.

The main risk to the "no new diesels" ambition was the absence globally of a large-capacity electric double decker, similar to Auckland's big diesel double-deckers which serve the high-patronage routes like the Northern Busway.

Auckland's commuter diesel bus fleets pumps out an estimated 93,000 tonnes of carbon dioxide fumes a year.

Abigail Dougherty An electric bus on trial on Auckland's Inner Link route. Electric buses will become a more common sight in the city over the coming years.

Auckland Transport's 2018 plan to introduce low-emission buses priced the social benefits of a shift out of diesels at $141.3 million over 23 years.

"A shift from diesel buses to electric buses would significantly reduce pollutants that harm human health," noted a Ministry of Transport briefing in October 2019.

However, the ministry advised Transport Minister Phil Twyford that it was not currently working on incentivising a shift to electric buses, and was "prioritising other work to reduce Greenhouse gas emissions".

Stuff understands this work is continuing.

As it stands Auckland Council may have to help fund an accelerated move into electric buses, and it was not yet clear how upgrades of the electricity network near bus depots might be paid for.

Auckland Transport and Vector are currently exploring what additional investment might be needed, as well as the role that could be played by charging buses outside peak times, when the load on the network is lower.

Wellington is moving faster than Auckland at present, with 10 smaller double-deckers, and negotiations by Greater Wellington Regional Council underway for more.

"This was an early foray into electric buses, on a scale we could manage, learn from and push ahead," said Greg Pollock, who has just finished up as general manager of GWRC's public transport arm Metlink.

It was not necessarily costing a premium over diesel because of the long-term contracts with the bus companies, Pollock told Stuff.

Auckland's electric bus roll-out will put six on Waiheke Island mid-year, followed by 12 on the City Link route, and nine on the Airporter 38 run early in 2021.