1. Expressways, where pedestrians and cyclists are not allowed. They are walled off with specific entrances and exits.
2. Country highways, where pedestrians and cyclists are nearly unheard of, and are typically very easy to spot from a distance and adjust accordingly.
There is a third area where these speeds are sometimes reached in urban areas that Strong Towns calls "stroads", and these have a whole host of problems. Going 10mph over the speed limit in these areas probably doesn't make a huge difference, because the are already so pedestrian and cyclist unfriendly to begin with. Not Just Bikes has a great video about them here: https://www.youtube.com/watch?v=ORzNZUeUHAM