Do you have some numbers to support your claims?

Yes,

From CDC:

> In large central metro areas, those aged 35–44 years (2.08), 45–54 years (2.60), 55–64 years (2.60), 65–74 years (3.36), 75–84 years (5.19), and ≥85 years (5.24) had statistically higher death rates than those in the same age groups at other urbanization levels. [1]

[1] https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6215a1.htm

most US metros don't have workable public transit; most people drive to get from point a to point b even in our dense metros. Perhaps because even our metros are not dense enough, perhaps for other reasons. I would be open to data that showed there were more traffic deaths in dense areas where most people took public transit, but this isn't it.

Does this hold adjusted for miles driven?

Well, my claim was mostly that the speed is not the only factor but also the traffic density.