Negligence per se: when breaking a safety law proves carelessness

A negligence case usually turns on what a reasonable person would have done. When a legislature or agency has already written that answer into a safety law, many courts let the plaintiff use it. Cornell's Wex encyclopedia defines negligence per se as negligence in itself: a defendant who violates a statute or regulation without excuse is treated as having breached the duty of care (Wex: negligence per se).

What the plaintiff has to show

The details vary by state, but the claim generally needs four pieces:

1. The defendant violated a statute, ordinance or regulation.
2. The law was designed to protect against the type of harm that happened.
3. The plaintiff is in the class of people the law was meant to protect.
4. The violation caused the plaintiff's injury.

Wex ties the second and third requirements to section 14 of the Restatement (Third) of Torts. They keep the doctrine tied to a law's purpose. A rule written to protect workers from falls does not automatically set the standard for a passerby hurt by noise. And the fourth requirement means a violation, by itself, never proves causation. Wex notes that the plaintiff still has to show the violation was both the actual cause and the proximate cause of the injury.

The laws that most often qualify

According to Wex, traffic laws are the most common application. A driver who runs a stop sign or speeds through a school zone has broken a law written to protect other people on the road. Safety codes and workplace regulations can qualify too. California's jury instruction materials note that Cal-OSHA regulations may be used like any other regulation to set a standard of care, and that federal statutes and regulations can also be adopted. The same materials report that California courts have applied the doctrine to building code violations only in limited situations.

The judge, not the jury, usually decides whether a law fits. In California, the trial court decides whether the injury was the kind the law targets and whether the plaintiff was in the protected class, and the jury decides whether the law was broken and whether the violation caused the harm (CACI No. 418).

Excuses

A violation does not always mean negligence. Wex summarizes section 15 of the Restatement (Third), which excuses a violation when, among other situations, the statute is unclear, the person used reasonable care trying to comply, or compliance would have caused more harm than the violation.

California's version appears in Evidence Code section 669 and CACI No. 420. The violator can rebut the presumption by proving it did what a person of ordinary prudence, trying to obey the law, might reasonably be expected to do in the same situation. CACI No. 420 lists the usual forms: an incapacity that made the violation reasonable, an inability to comply despite reasonable care, an emergency the person did not cause, and a greater risk of harm from obeying (Evid. Code § 669). A child's conduct is measured against what a careful child of similar age and experience would do, unless the child was doing something normally done only by adults, such as driving.

Conclusive, presumed or just evidence

States give a violation different weight. In some, an unexcused violation is negligence as a matter of law. The best-known statement of that view is Martin v. Herzog (1920), in which New York's highest court treated driving a buggy at night without the lights a statute required as negligence in itself, while still requiring proof that the missing lights caused the crash. Other states treat a violation as raising a presumption that the defendant can rebut, and some treat it only as evidence of negligence that the jury may weigh along with everything else. Minnesota's traffic code is one such rule: it says a violation is prima facie evidence of negligence and not negligence per se (Minn. Stat. § 169.96).

California follows the presumption model. Section 669 presumes a failure to use due care when its conditions are met, and the presumption can be rebutted with a recognized excuse. The cases quoted with CACI No. 418 add that negligence per se does not create its own claim. It operates inside a negligence case. Our CACI No. 418 explainer walks through the California instructions step by step.

It can cut against the plaintiff too

Defendants can use the doctrine too. A defendant can point to the plaintiff's own violation, such as a cyclist riding the wrong way or a pedestrian crossing against the signal, to argue the plaintiff was negligent. In most comparative fault states that finding reduces the award, and in states with a 50 or 51 percent bar it can end the case if the plaintiff's share is large enough. Our guide to comparative vs. contributory negligence explains how the share is counted.

Questions to test a negligence per se argument

• Which law was broken? Find the exact statute, ordinance or regulation.
• What was it written to prevent? Read its purpose section or the agency's explanation.
• Who was it meant to protect? Check whether you fall inside that group.
• Did the violation cause your injury? Be ready to prove the link separately.
• How does your state weigh a violation? Conclusive, presumed and evidentiary approaches lead to different trials.

This guide explains general legal concepts and is legal information, not legal advice. Consult a lawyer licensed in the relevant jurisdiction about a specific situation.