In these cases the appropriate standard of care is defined by the law that was violated. For the court to accept a negligence per se claim, the plaintiff must show that a law was violated, that the law was intended to prevent the type of injury that occurred, and that the plaintiff was in the class of persons intended to be protected by the law. The plaintiff may claim negligence per se even if the defendant has not been convicted or administratively sanctioned under the law in question. In such cases, the plaintiff must prove that the defendant has violated the law. The plaintiff does not need to prove independently the violation if the defendant has been convicted or had pleaded guilty.
Traffic violations are the most common instance of negligence per se.
Assume that a driver hits a child while driving at night without headlights. This behavior is illegal, it is prohibited to prevent this type of accident, and the plaintiff is in the class of persons who were intended to be protected. The driver could be found negligent based on the violation of the statute. Conversely, assume that a physician injures a patient while practicing without a current medical license. This will not support a negligence per se claim because medical licensing laws are not intended to protect specific patients from medical malpractice.