Luckily at my barn, the people are very kind and, even though we ride on the dirt road, they don't speed and will move over when they see horses out. There is a blind curve though, which can be scary some times.
However, at my old barn, the riding arena was right beside a pretty busy country road that led to the interstate and 18 wheelers and people would CONSTANTLY honk and speed when we were riding in there. It gave most of the horses a near heart attack, all the noise and big trucks whizzing by! I can't even tell you how many times riders fell off because their horses spooked at the honking. We eventually got my trainer a sign to put up (mostly as a joke) that said, "SLOW DOWN! THIS ISN'T A $#%^% FREEWAY!". (the symbols were actually there, too)