It doesn't make much sense to think of efficacy windows for driving, it's not a medical intervention.

Besides US traffic deaths are crazy high by UK standards.

I believe the numbers normalize a bit when you adjust for the fact that everyone drives in the U.S. and tends to be alone when driving. So it’s like accident per mile driven and you see it’s around the same. But in the UK many fewer people drive as a proportion of the population and especially those who are more dangerous (e.g. young, old, disabled, drunk) tend to opt out here due to the availability of mass transit which doesn’t work in the U.S.