The proper answer, if you want more fuel efficient vehicles, is to simply raise the gas tax and allow every company's engineering teams decide what to build, and every consumer to decide what they want. This keeps domain expertise where it belongs while achieving the stated goals, and does not strictly reduce choice. If engineers could not figure out more efficient designs, and customers wanted more efficient vehicles, they could simply make smaller trucks to sell.

Instead they demanded companies engineer vehicles to conform to weird mpg/area curves that accidently skew towards "huge." It was in effect backseat engineering.