Per 1 billion vehicle-km the US has 6.9 deaths and the Netherlands has 4.7 deaths. That’s obviously better much but I wouldn’t call it “problem solved”.
https://en.wikipedia.org/wiki/List_of_countries_by_traffic-r...
(Wikipedia links to itf-oecd.org/ where those numbers come From)
My guess is better road design means less miles driven by cars (as opposed to other, safer vehicles) and therefore fewer accidents overall, even if car crash statistics remain the same.