Fun fact: ANCAP tests to a 1600kg impact. A Silverado doesn't even have to punch its own weight. Kei cars need to punch double.

For pedestrian safety, they measure impact the knees and head. A Camry would knock you in the knees and you go head-first into the windscreen.

A Silverado? You get slammed in the chest and it passes becuase the whole car is lifted above your knees and your head only touched the ground. Ribs aren't in the criteria.

Yep. This is why I think my 900kg hatchback should cost less to register than a 2500kg roadblimp ute.

I don't think a quartic tax will scale too well because the impact of a vehicle isn't just its wear on the road.

However larger cars burn more fuel and release more particulates such as brake dust and microplastics from tyre wear. Backstreets that once could park on both sides without impeding flow are now reduced to a single lane. Turning lanes will now only hold 4 cars instead of 6, and less cars get through per green. They bring more kinetic energy into a collision, and are not as manouverable. They're less safe to have around by every measure.

If the TAC processed their road stats properly, they'd realise that a kei car won't kill anyone. People in kei cars will still get killed, but that's a misattributed stat that should go towards the vehicle that brought the most weight into the collision.

A fair tax would need to be based on size, weight and emissions. They all matter independently.