OK, I will try to translate. Thickly settled means a high density population, usually in a smaller town or village. A frost heave is when a road buckles up and makes a bump, usually causing a crack in the pavement, too. This comes from the frost/freeze cycle here, where it is not consistently cold all winter. Reverse curve means an "s" curve. There were a few others, too, that are not much in usage in speech, but they have never updated the language in the road signs.
So yeah, rotaries. The first week I lived here, I went around the Chelmsford rotary a few times, to go to the grocery store! My kids thought I was nuts. It was a "minor" exit, i.e. a regular road, not a state highway. Of course, now, that rotary is all well signed and much easier to navigate. If they have 2 clear lanes, they are OK, but the problem here, is people enter and exit without yielding and don't follow the established rules about which lane, inside or out, to be in if you are going more than halfway around. I live within 2 miles of one of the most notorious rotaries in the state. It's a rite of passage when kids in this area get their license! They have redone a major part of the highway, but the plan to elevate the highway, get rid of the rotary, and put the 2 town roads that are exits below it is still a couple of years off. This highway cuts my town in half and when they fix this, it will make a huge difference for the residents. They are starting to put more directions/instructions in rotaries and are calling them round-a-bouts, too. I have seen some in Europe with 10 exits! The difference is, that everyone follows the rules. We had to ride our bikes on one of those huge ones, coming into Santiago de Compostela, last summer, and I was scared as hell, but the leader prepped us and it was fine.