The fact that we have political systems that do byzantine things like this instead of just charging a basic tax per litre of fuel to account for environmental costs (or even mileage * weight^4 for wear and tear) in a consistent way continues to frustrate me. When accounting for externalities, policy should "tell" consumers/market what to optimize for (and how much it matters), not how to optimize for it. The latter is more intrusive, and easier to game.