If I witnessed a traffic accident in California, USA, my immediate response would be to ensure my own safety first and foremost. Once I've confirmed that I'm in a safe position, I would quickly dial 911 to report the incident to the emergency services, providing them with detailed information about the accident, including its location, the number of vehicles involved, and any visible injuries.While waiting for the emergency services to arrive, I would try to assist anyone who might be injured, providing basic first aid if possible and necessary, while being careful not to move anyone who might have spinal or neck injuries. If the situation was safe and I was able to, I would also try to collect information from any witnesses, taking down their contact details in case the police or insurance companies needed to get in touch later.In the meantime, I would also try to document the scene as best as possible, either through photos or videos, capturing the position of the vehicles, any skid marks on the road, and the general layout of the accident scene. This evidence could be crucial for later investigations.Once the police arrived, I would provide them with all the information I had gathered, including witness details, photos or videos, and a description of what I had seen. It's important to cooperate fully with the authorities in such situations, as they are trained to handle these emergencies and need all the relevant information to conduct their investigation.