There are also very big differences in road casualty rates[0]
The UK has 2.61 road deaths/100,000 inhabitants, 3.8/billion vehicle-km.
The US has 12.84 and 6.9.
The US dropping to the UK rate would be a difference of around 35,000 lives per year.
States vary a lot[1]. The lowest is:
5.7/100,000 for Rhode Island 7.1/Billion Vehicle-km for Massachusetts
Highest:
26.2/100,000 for Mississippi 20.8/Billion Vehicle-km for South Carolina.
[0] https://en.wikipedia.org/wiki/List_of_countries_by_traffic-r... [1] https://en.wikipedia.org/wiki/List_of_U.S._states_by_road_de...