You're partially right. Traffic deaths have dropped, but they could be even lower, if we didn't keep raising speed limits.

Check out this article from Consumer Reports for more details: https://www.consumerreports.org/car-safety/higher-speed-limits-led-to-36760-more-deaths-study-shows/

Choice quote:

"The researchers from the Insurance Institute for Highway Safety found that for every 5 mph increase in a highway’s speed limit, roadway fatalities rose 8.5 percent.

Although road deaths are lower overall than they were in 1993, they’re still higher, the study concludes, than they would have been had speed limits remained the same."

Regardless, the point stands - if we all agreed to forgo excessive speed, we can lower the rate of new carbon emissions and save lives. We just choose not to. We tell ourselves: well, fewer people are dying now, so we don't need to lower the speed limit. It's weird logic. How many deaths are okay? I suspect the answer is easier if you haven't lost a loved one to a traffic fatality.

Also, here's your requested actual case of a Ford F-350 crossing the center line and killing someone: https://www.ammonslaw.com/blog/2019/september/ford-to-compensate-daughter-of-man-killed-in-cra/