That’s not entirely due to emissions. That’s also due to mandated safety devices and construction elements, which massively raise the weight of a car. Many small cars easily top 3000lbs today, whereas many in the 80s were close to 2000. That extra weight reduces fuel economy.
More like 4000lbs. with federally mandated crash steel.
The point that I’m driving home is that fuel economy takes a back seat to emissions in the US auto market.
I worked in the auto industry. Everybody knew that the deck was stacked against us.
The EPA made in no short terms that WE were not allowed to put small diesel passenger cars on the domestic market.
GM got away with it they are, well, “government motors”.
Ten years ago, I was involved in tests at Chrysler with small diesel engines in their vehicles across their entire line up.
The trials stopped when the EPA said we couldn’t sell them on the domestic market. Those engines were made by the same company that supplied engines to VW.