If you are considering the safety of the roads themselves, then death/injuries per mile driven is the correct statistic. If you are considering the safety of the society as a whole then it makes sense to consider the obvious advantage of driving less.

The UK driving test is much more stringent than the NY state test (I can't comment on other states - I believe each state defines their own driving test).

The NY test - 10 minutes in the car. I drove around the block; parallel parked, 3 point turn and back to the start. Done.

UK test - an hour in the car; had to drive in urban, country and highway settings (a dual carriageway, not a motorway - learners are not allowed to drive on motorways in the UK); parallel park and answer a lot of questions while doing so.

That's not to discount the fact that the UK has a lot of bad drivers - but the NY test was simply a joke.