If that happened you'd see the law of unintended consequences kick in immediately. You'd have 50mpg standards for passenger cars and 20mpg standards for large, roadworthy farm vehicles. So most people would buy large farm vehicles.
"So you have to prove you are a farmer before you buy one!" you say. Great. Lots of people would then become "christmas tree farmers" to save the money and get the cool big (and cheap) truck. The minor hassle would be worth the $10,000 savings to them.
"So make standards for christmas tree farmers, and require them to prove sales" - they sell a few trees to wood chippers.
"So require them to keep records of the people they sold them to specifically for Christmas." That might work. But if they "sell" them only to friends?
And in ten years you will wonder why you need to display a permit if you put up a Christmas tree.
If implemented well, that would save a lot of lives.Imagine a system that allowed fleet average crash safety ratings.
Because sometimes they carry 80 people - and when they do that, they are by far the most efficient vehicles on the road. And the problem isn't their weight; it's their fuel consumption. The best way around this? Have a passenger-miles per gallon fleet requirement.Why should we have (for example) city buses that weigh 30,000 pounds empty?
See above.If every personal vehicle is only allowed say 4 liters per 100km, then we would see the tradeoffs inherent in using an excessive vehicle.