Perhaps I could point out that in this state at least, the death rate per head is far higher in areas of low population density than in metropolitan areas, which sort of contradicts what I think is your point.
From my experience driving in the US, some parts of the US are more crowded, and some are not, and yes, in some parts average speeds are higher. Having spent many hours at speeds of 10-20mph on a ten lane freeway, it is not clear that on average speeds are higher than here. There are probably fewer major highways that are only two lane as they are here, which facilitates higher speeds there in rural areas, helped by lower emphasis on strict speed limits than here (at least in some states!).
Like Australia, rules and licencing standards vary state to state - and there are fifty of them!
John

