Turbo-charging the drive to quash emissions on Kiwi roads.

The Government's unveiled tweaks to the clean car discount scheme, saying it's well exceeded projections so far.

Changes include boosting rebates for zero emissions vehicles, while ramping up fees for gas guzzlers, like utes.

Officials at the Government's transport agency appear to be working on a plan to bringing trucks into the Clean Car discount scheme.

It comes as the Transport Minister turbocharges the policy, saying it’s now estimated to reduce 230 percent more emissions than originally estimated by 2025.

According to official information data seen by Newstalk ZB, a freight decarbonisation unit has been set up within the Ministry of Transport.

It's purpose, according to the documents, is to set the ground work for a Clean Truck Discount, which would offer tax breaks for importing lower emitting trucks.

But, gas guzzling tracks would face a tax hike, if the policy followed the same path as the clean car discount.

Transport Minister Michael Wood says it's about ensuring the scheme is self-funding until its next review.

He says the programme's forecast to save New Zealand from importing more than a billion litres of petrol.

The Prime Minister says tweaks to the Clean Car Discount Scheme will help them get more out of it.

The programme pays a subsidy to buyers of low emission vehicles, designed to be paid for by a fee charged on heavy polluters.

Changes announced today include narrowing the focus to more fuel-efficient vehicles earlier, reducing rebates, increasing fees and adjusting eligibility.

Prime Minister Chris Hipkins says the scheme's been successful so far.

"We've got to make sure the scheme is sustainable and we've got to make sure we're getting the best bang for buck out of it. That does involve periodically reviewing the criteria."