They could change the rules that effectively penalize smaller vehicles. They can still have categories but be equally stringent within each category. The reali

They could change the rules that effectively penalize smaller vehicles. They can still have categories but be equally stringent within each category. The reality is that manufacturers have captured the EPA regulations and are using them to steer the market in the direction they want, and in doing so actually making the environment (to say nothing of road safety) worse. Manufacturers want more profit per-car. They also want to push the market into categories that have higher tariffs on imports. They don't want to be in the market of compact cars or sedans or even, increasingly, large but lightweight vehicles like minivans so they steer the market and regulations away from these vehicle classes.