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”.
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.
'No Way to Prevent This,' Says Only Nation Where This Regularly Happens
This is a solved problem: look at the current state-of-the-art road design documents from the Netherlands. Apply. Problem solved.