The proliferation of the automobile after World War II changed life as we know it across the globe. People gained new levels of freedom to access jobs and services. Better roads were developed. Revolutions in urban planning gave rise to suburbia. Huge new job creating industries were formed. We also saw a sharp uptick in leisure travel thanks to the convenience of automobiles.

An unexpected side effect of this overwhelmingly beneficial technological revolution was a dramatic rise in global pollution. Automobiles can release as much as 70gm of exhaust gas, containing between 150 to 200 different compounds, per ton of gas combusted. Included in these compounds are carbon monoxide, nitrogen oxides, lead dust, carbon black, and other dangerous gases and particulates. Nitrogen oxides released in automotive exhaust and exposed to sunlight can undergo a chemical transformation that ultimately results in the formation of ozone and photochemical smog containing harmful compounds like formaldehyde and acetaldehyde. This problem can be exacerbated in heavily congested cities and in geographical locations that physically trap the smog in place (Trento, 2024).

A growing understanding of the chemical dangers of unrestricted automotive exhaust lead the US Congress to pass the Clean Air Act in 1970, requiring a very ambitious 90% reduction in emissions from new vehicles by 1975. The EPA was also created in 1970 and was tasked with regulating automotive exhaust.

Over the following 55 years, the EPA has continued to refine and augment its environmentally motivated regulations and expand its scope to include trucks, locomotives, marine engines, and aircraft engines but what impact has this half a century of regulation yielded?

Greenhouse gas emissions from the global transportation sector measured 1.8 billion tons in 1970 and have steadily increased year over year (with the exception of 2020 pandemic interruptions) reaching 8.9 billion tons in 2024. This figure seems to illustrate a failure of regulation until you consider some crucial context: in 1970 there were under 250 million motor vehicles in use globally, but by 2021 that number had ballooned to over 1.5 billion vehicles in operation.

If we find the total greenhouse gas emissions from the transportation sector per one hundred million vehicles in operation, we can see that, on a per car basis, greenhouse gas emissions actually declined by 41% between 1990 and 2021.