What is 'negligence per se'?

Negligence per se applies when a defendant violated a statute designed to protect the public from the type of harm that occurred. In these cases, the violation itself establishes the negligence element — the plaintiff doesn't need to separately argue what a 'reasonable person' would have done. Example: a driver who ran a red light (violating a traffic statute) and hit a pedestrian is negligent per se — the statute violation establishes negligence. The plaintiff still needs to prove causation and damages.