You drive past a crash on the highway. You are not involved, and emergency responders have already arrived on the scene. What does the manual tell you to do?

Warning duties belong to responders and their equipment, not passing motorists, and stopping on the shoulder can itself become a hazard. This answer borrows the disabled-vehicle habit of pulling to the shoulder and using the parked car as a warning marker, though responders and their emergency lights already fill that role at a managed scene.

Slowing to a stop behind the crash is exactly what the manual warns against, since traffic that stops or slows for an initial crash is a common cause of secondary collisions. This answer applies the first-on-scene instinct to activate hazards and stop, when the manual reserves stopping for drivers who are involved or arriving before help does.

The manual specifically directs uninvolved drivers not to stop when help is already at the scene, and offering witness assistance is not one of the exceptions listed. This answer reads the manual's later instruction to get the names and addresses of witnesses as a duty for any passing driver, when that step applies only to drivers involved in the crash.