The regional fuel tax will apply to all petrol and diesel sold in the Auckland region from July 1, 2018.
• It will apply to all other regions from 2021 given most other councils have already indicated they will be applying for it.
• It can be charged up to a maximum rate of 10 cents per litre plus GST (11.5 cents incl.) at the pump, for a maximum of 10 years.
• It will be paid by fuel distributors when they deliver fuel to service stations and commercial users inside the region.
• Rebates will be available to those that do not use fuel on roads. Eligibility for rebates will be confirmed when the regulations are finalised.  Exactly how this will work regarding freight vehicles is still vague.

Here is the Auckland Region Map with boundaries shown: https://geomapspublic.aucklandcouncil.govt.nz/viewer/index.html

For further information go to: https://www.transport.govt.nz/land/regional-fuel-tax
This includes a Q&A sheet which at best gives a general overview.