California is a fault state, meaning that somebody must be found responsible for causing an accident. California is also a comparative liability state, meaning that more than one person involved in causing the accident can be held liable for the damages caused. The level of liability that each party is found guilty of depends on the level of negligence that each party engaged in that caused the accident. Negligence occurs when someone breaches their duty of care, also known as their responsibility to conduct themselves in a lawful and careful way to protect others as well as themselves.
Everyone owes one another a duty of care while on the road, including cyclists and drivers. Cyclists should do their part by riding correctly on the road, and drivers who park curbside on the road should always check for bicyclists coming up behind them before they or their passengers exit the vehicle. In bicyclist-doored accidents, more often than not, the person who opened the door on the bicyclists will be found at fault for causing the accident, not the bicyclist. This is because the driver has a greater duty of care and should always check out the road for upcoming traffic before they decide to open their door. Opening the door before checking for oncoming traffic is negligent on their part. Bicyclists can also keep a lookout for people in their vehicles, anticipating their exit, however this is much harder to do for a bicyclist who needs to be focused on the road.