>The free market might over time get us cleaner engines when interests align but in all honestly the biggest factor driving cleaner engines has always been regulation...

One scientist learned that smog was a result of automobile emissions as early as 1948 (https://en.wikipedia.org/wiki/Arie_Jan_Haagen-Smit). That was 56 years after automobiles were first produced. Shortly thereafter, the Federal government started tackling the issue in 1955 (https://www.epa.gov/clean-air-act-overview/evolution-clean-a...). Why would companies invest in cleaner emissions if the government was going to make mandates that would throw a wrench in their investments? It has been better for them to wait and see what they have to do. They were never given the chance to self regulate.