I think the New York Times did a fabulous job mapping changes in U.S. auto emissions over time. https://www.nytimes.com/interactive/2019/10/10/climate/driving-emissions-map.html
The data comes from Boston University’s Database of Road Transportation Emissions. The Times presented it in a way that allows readers to look at different metro areas across the country and examine trends in total emissions as well as per-person emissions.
The worsening levels of car emissions in many areas represent an important piece of the carbon pollution that is contributing to climate change.