If you are the first person on the scene of a collision, your actions need to be quick to attempt to save lives and help those who are injured. Here is the course of action most recommended for witnessing a collision:
Stop and Help: If you are the front person to witness a collision, pull over, turn your hazards on and place warning signs to alert others on the road.
Find if Anyone is Injured: Turn off all vehicles that were affected in a collision and check to see if anyone is injured. Be prepared to perform CPR, act on anyone with First Aid and call 911 if necessary.
Inform the Police: Ask the next person who stops to notify the police. They need to give the location of the collision, including exit/entrance information, what injuries need attention. Do not hang up until emergency dispatchers arrive or they hang up themselves.
Wait for the police: Remain at the scene until first responders and police arrive. You will need to tell them what happened and all the information you know on the scene. If you see a collision with emergency vehicles already present, continue past the collision. DO NOT stop or slow down to look at what is happening, this will cause traffic behind you and cause the EMS vehicle to be delayed to the next destination