Perhaps they could install some sort of blinking warning light on top of the hill and maybe joyriding teenagers would heed that warning, or maybe not. Otherwise I think you'd have to cut through the hill or move the roads completely, either of which there probably isn't much money for.
On the side of a hill? That's a ton of earthwork.
Country lanes don't get roundabouts. There's no money for that.
This also seems to be farm country. Converting productive fields to non-productive traffic calming structures would be about as popular as banning pickup trucks.
The vast majority of rural roads get plowed. Everyone who lives in a rural area has at least one plowed route from their driveway to the rest of the world.
A example of this (here done for laugh) is [0], where a single lane muddy curvy hillside road has a speed limit of 80 km/h (50 mph).
The point I would like to make here is that on a street like this is it impossible to joyride and even with low visibility intersections the risk of a T-bone or a fatal crash is minuscule.
This particular example is a strawman of the problem: there are many reasons why most roads cannot be like this, it is just an example of "If the drivers have to pay attention they will pay attention"