This graphic from Stuff gives a good idea how variable network pricing may work. The AA noted:
“This is a very different proposition to what we saw come out of Auckland Council last year with a proposed motorway user charge,” Irvine said. …
Motorists would receive a bill based on the number of kilometres they travelled on which roads and at what times.
The idea being that it would replace the petrol tax. Like the AA I think it is a good idea. It is basically user pays rather than subsidies.