2 years ago, our 4 year old mutant daughter managed to sneak out the deadbolted front door of the apartment we lived in. It was cold and raining out, but she did put her boots on...but that's all that she put on.
In the moments it took me to realize she was too quiet, and start looking for her inside (hide and seek in closets being her favorite game at the time), and then more frantically outside, she got down three flights of stairs, through the parkinglot, and down to the main, very busy, road, and started to walk around on the side of the road.
One of Edmond School District's finest stopped their bus in the middle of that street and put their lights and sign on. Traffic froze, while my neighbor, who had been helping me search, saw her, bundled her up in a blanket, and carried her back up the hill. The entire span of this was less than 10 minutes.
*That* is why you stop on multi-lane streets, or anywhere. If that driver hadn't put her lights on, and if the other drivers hadn't obeyed the law, my daughter could have been killed in an instant.
I made sure the school distrect knew about how fantastic the driver was... *after* I stopped being hysterical.