COVID and regulatory stuff has given me more work, and i shouldn't even look this up (professionally, understanding mortality is part of my job, but more in application and less in development of rates) - I do a lot of financial projections of populations, but in the long term (short term noise isn't on my radar).
I figured I'd look this up, anyway, and this is an article that addresses it some.
https://www.aeaweb.org/research/why-doe ... e-increase
The article suggests 17% of the increase is due to motor vehicle stuff. No one cause -little bits discussed, but they don't explain the total. Troublesome comparison because there are some counter trends (income and mortality have a well-known relationship - people with higher income generally live longer, but that is, again, a long-term trend).
Geography, education, etc, all go along with income - I don't know which is causal as I use the results of studies and don't participate in putting them together.
If I were going to try to solve this, I'd start with the large causes of death (heart disease, cancer, diabetes - which is comorbid with lots of things) and see if any of them yielded fruit as the combination of heart disease and cancer has an enormous influence (cancer's impact on life expectancy is pretty constant - a 2% improvement in that respect or so each year). Heart disease declined sharply for decades but has leveled off (most of the change in heart disease is said to be linked to the decline in smoking rates) some. Last year was the first I can recall where aggregate population experience was more favorable than expected by any significant amount.
In the states, we had a huge run up in life expectancy from about 2003-2007 or 8 (not looking it up) then a fairly flat period for quite some time with a little bit of noise (going from memory). Highly publicized stories about decreasing life expectancy have been due to mortality at younger ages as I can recall with continued improvement at later ages - in general).