Utes and any diesel powered vehicle, already pay road user charges.
The fleet has been getting more efficient over time, this is expected.
As a side note, the damage that a vehicle does to the road rises at the 4th power of weight.
So a vehicle that is double the weight does 16 times the damage. Using a 1200kg car as the baseline with a damage factor of 1, a 50T truck will produce a damage of ~335,000 (assume that the weight is evenly distributed across the 9 axles)
Oh yeah duh, probably aren’t any modern Utes that are petrol nowadays - though i’d guess some medium-large SUVs probably still are.
The damage thing is mad huh - which is why the way RUCs are charged on heavy freight is (last time I looked anyway) such a heavy subsidy to that industry.