Overall, “improvements over time have better longer-term effects simply by not alienating consumers, as compared to great leaps forward” in fuel efficiency and other technology, the administration argues. It contends that freezing the mileage requirements at 2020 levels would save up to 1,000 lives per year.

New vehicles would be cheaper — and heavier — if they don’t have to meet more stringent fuel requirements and more people would buy them, the draft says, and that would put more drivers in safer, newer vehicles that pollute less.