I remember being told by CHP if you are going to help to always park 'downstream' of the wreck so that your car doesn't become a second accident. They park upstream because they have lights and use the car to protect the accident scene. Someone might want to confirm this but i also remember that if you are out at about 2-3am and come across someone on the right shoulder, park and don't use the emergency blinkers. Evidently, this is because the drunks out at that time will aim for anything with light on to 'follow home'.