This nearly happened to me tonight, was getting up a wall, made it, then when i wanted to drop out of it, a car decided to turn in the entrance just to go back the other way, but I never saw it coming, I nearly dropped on it ! but I thought after that, "if it would've been a pedestrians, that could have been more serious" Even though i always wait till they pass, there is still the risk as you said that someone pass by rushing !