To determine fault in a car accident you have to prove negligence. Evidence such as police reports, traffic laws, witness statements, video footage, and vehicle damage can help to support claims of negligence and establish liability. Some states follow pure comparative negligence, others use modified comparative negligence, and some use contributory negligence.

Filing a claim can be done either through insurance, or if necessary in court (with statutes of limitations ranging from 2-4 years depending on your state.

Finding out who is at fault can be important to determine who is financially liable for medical bills, property damage, (if applicable) lost wages, etc. Additionally, it can impact insurance rates, and can lead to legal consequences, especially in cases of reckless driving or DUIs.

To protect a claim, drivers should avoiding admitting fault at the scene, limit conversations with the other parties insurer, and make sure to document everything.