To be honest, sometimes I ride by people who are on the side of the road and i'm not quite sure if they have a flat. I usually realize too late and by then it's too late to turn back. I passed a group of three girls once, and one clearly had a flat, but for some reason it didn't register in my mind to ask if they were ok...I just looked and kept going. I didn't mean it though! Sometimes the wheels keep rolling and I just space out.