I guess drivers just don't realise they need to slow down or give way to anybody unless there's a stop sign, traffic light or they're turning into a different road.
Surely drivers know what Yield means though right? I guess the US might need yield signs at a roundabout given not all drivers will get the basics of how they work. There should never be a stop sign on a roundabout, the whole point is you're supposed to be able to keep going without stopping at all if theres nobody coming round it.
