At that stage, Labour had announced that it would support a regional petrol tax in Auckland, which was expected to be about 10 cents a litre, to fund Auckland transport projects including light rail from the city to the airport.
But it gave no hint before the election that it would raise petrol tax nationally.
Ardern told Hosking the petrol excise duty was not a new tax, only an increase to an existing excise.
"A Government Policy Statement on national road transport is the way we divide up the money that comes out every three years, and routinely under the last Government we saw those statements discussing what we do on the excise," she said.
"Of course I don't believe I'm breaking a promise, but yes, it would come in this term."
Challenged by Hosking that on that basis she could also raise income tax because that was also an existing tax, Ardern replied: "We totally ruled out changes to income tax."
She defended a shift in the new policy from funding the last Government's "roads of national significance" to spending more on public transport and regional road safety improvements.
"Under the last Government we were spending a huge 17 cents extra that the Government took in from motorists on roads that roughly 4 per cent of cars were using," she said.
Unveiling the new policy yesterday, ministers cited the example of Sweden's "Vision Zero" which has halved its road toll from 540 a year in 1997 to 270 in 2016 by improved roads, traffic education and a mix of lower speed limits on some rural roads and higher speed limits on some motorways.
Anders Ydstedt from the Swedish Royal Auto Club told Newstalk ZB that the reduction was achieved, despite an increase of 1 million cars, by measures such as installing median barriers on more roads.
New Zealand's road toll also halved from 539 in 1997 to a low of 253 in 2013, but has risen again in the past four years to 379 last year.
