How Fault Is Determined After a CA Accident

Police Report

The police report: important, but not the final word

When officers respond to a serious collision, they typically prepare a traffic collision report. It can be persuasive — it may note who was cited, what each driver said, road and weather conditions, and the officer's opinion about how the crash happened. Insurers lean on it heavily during claims. But here is a point many people get wrong: the report itself is generally not admissible as evidence in a California civil trial. California Vehicle Code section 20013 provides that no such accident report shall be used as evidence in any trial, civil or criminal, arising out of an accident. The reasoning is partly about hearsay — the responding officer usually did not witness the crash — and partly about preventing a jury from treating the report as an official verdict and giving it undue weight. That does not make the report useless. It can carry real weight in the insurance claim stage, and the underlying facts it documents — witness names, photographs, measurements, a citation — can often be proven in court through other admissible means. Think of the report as a roadmap, not a ruling.

Negligence Elements

Fault means negligence: the four elements

In most California injury cases, proving the other party is at fault means proving negligence. California's pattern jury instructions — the Judicial Council of California Civil Jury Instructions, or CACI — break a basic negligence claim into elements a plaintiff must establish. Under CACI No. 400, a plaintiff must establish duty, breach, causation, and damages. If any one of these is missing, the negligence claim fails. This is also why two honest people can describe the same crash and disagree about fault — they are really arguing about breach and causation. If you are not sure your situation checks these boxes, our quick Do I Have a Case? quiz walks through the basics in a few minutes. It is educational, not a legal opinion.

• Duty — the defendant owed you a legal duty of care. Every driver, for example, has a duty to use reasonable care behind the wheel.
• Breach — the defendant breached that duty by failing to act as a reasonably careful person would. CACI No. 401 defines the basic standard: a person is negligent if they do something a reasonably careful person would not do, or fail to do something a reasonably careful person would do, in the same situation.
• Causation — the breach was a substantial factor in causing your harm. CACI No. 430 describes a substantial factor as something more than a remote or trivial factor; it need not be the only cause.
• Damages — you were actually harmed, including injuries, medical bills, lost income, and pain and suffering.

Negligence Per Se

Negligence per se: when breaking a traffic law shortcuts the analysis

Sometimes fault is easier to establish because the other driver broke a safety law. California recognizes a doctrine called negligence per se, reflected in CACI No. 418 and grounded in California Evidence Code section 669. In plain terms: if someone violates a statute designed to prevent the kind of harm that occurred, the law presumes they were negligent. This is where the California Vehicle Code does heavy lifting in car-crash cases. Running a red light, speeding, unsafe lane changes, failing to yield, or driving under the influence are all Vehicle Code violations. If a driver's violation caused the crash, negligence per se can shift the focus: instead of debating whether the driver was careful, the jury may presume negligence, and the burden moves to that driver to show the violation was legally excused. The presumption is rebuttable, so it is not automatic — but it is a powerful tool.

• The defendant violated a statute, ordinance, or regulation.
• The violation was a substantial factor in causing the harm.
• The harm was the kind the law was designed to prevent.
• The injured person was in the class of people the law was meant to protect.

Shared Fault

What if more than one person is at fault?

Crashes are rarely tidy. California uses a pure comparative fault system, a rule the California Supreme Court adopted in Li v. Yellow Cab Co. (1975) and reflected in CACI No. 405. Under it, a jury assigns each person a percentage of responsibility, and your recovery is reduced by your share of the fault. Crucially, pure means you can recover even if you were mostly at fault — your damages are simply reduced by your percentage. Someone found 30% responsible for their own injuries can still recover 70% of their damages. This is very different from states that bar recovery once you cross 50%. It also means insurers have a financial incentive to argue you were more at fault than you really were, because every percentage point shifted onto you lowers what they pay.

Evidence

The evidence that actually decides fault

Because fault is proven, not assumed, documentation wins claims. The sooner this is gathered, the better — footage gets overwritten and memories fade. The evidence commonly used to establish fault includes a range of physical, testimonial, and expert sources.

• Photos and video of vehicle damage, skid marks, road conditions, traffic signals, and the overall scene, plus dashcam, surveillance, or doorbell-camera footage.
• Independent witness statements and their contact information.
• The traffic collision report and any citations issued, which are valuable in the claim stage.
• Medical records linking your injuries to the crash, and vehicle data such as event data recorders or black boxes in newer cars.
• Expert analysis, such as accident reconstruction, in disputed or serious cases.

Disputed Fault

What to do if the insurance company blames you

Hearing our investigation found you were at fault is stressful, but an adjuster's opinion is not a legal finding. Insurers work for their own bottom line, and under pure comparative fault, shifting blame onto you directly reduces their payout. Most California personal-injury lawsuits must be filed within two years of the injury under Code of Civil Procedure section 335.1, with different and often much shorter deadlines for claims against government entities. A disputed fault call is exactly where legal help matters most, so confirm your situation with an attorney before accepting any fault determination.

• Be careful what you say. Avoid apologizing or guessing about fault; stick to facts.
• Do not give a recorded statement to the other driver's insurer without understanding your rights first.
• Preserve your evidence — photos, the report number, witness contacts, and medical records.
• Get medical care and keep documenting your injuries and their connection to the crash.
• Mind the deadline and talk to a lawyer before accepting any fault determination.