The revenue for it comes from - road users. The people using the roads pay for the roads (well the state highways anyway). Understand the concept? Fuel tax and road user charges are fully dedicated to the National Land Transport Fund, which funds motorways. Most people would see that as being fair, if a bit blunt.
Let's look at your beloved "urgent public transport improvements", you want the whole Auckland rail network electrified and a NZ$1 billion-plus (yep note the plus, I'm guessing half a billion more) tunnel for a two-way rail loop through central Auckland to the western line at Mt Eden. Where do you want the revenue to come from to pay for that? The people who will use the trains? No. In fact at best they will pay perhaps a half of the operating costs of the trains (if they can match Wellington).
You want ROAD USERS to pay for your rail schemes, even though only 7% of all trips in Auckland are by public transport, and of those a majority are by bus and ferry.
Not only that you want road users to pay to subsidise the operation of the rail scheme too. However you begrudge road users expecting their motoring taxes being spent on the roads they actually use?
Yes I know you'll argue that the road users benefit because someone has decided to ride a train, instead of drive. Well of course that person riding the train has apparently benefited more, because the road user is subsidising their travel. Why should that person not pay the costs of their travel?
Jeanette, don't you realise the reason the roads are congested is because capacity is built according to politically determined funding criteria, and roads are charged the same no matter wherever and whenever you drive, unlike how airlines, hotels, phone calls and other services are charged. Don't you realise your beloved Soviet style management of highways is the problem, not the lack of a goldplated public transport system?
So go on Jeanette - tell motorists that the Greens believe that the majority of fuel taxes and road user charges they pay should be used to pay for transport modes they don't use. Tell them how many minutes they'll save in trips, how much fuel they'll save from this approach - show you've done the research.
Oh, it's just a "belief" isn't it. Yes, that damned religion of yours.