Negligence by a driver of a vehicle can take many forms, and it can be influenced by many different factors. For example, speeding, running a stop sign, and drifting into a bike lane all constitute driver negligence, or even recklessness if done with knowing disregard for the safety of others; especially pedestrians and bicyclists who have no vehicle compartment protection. In a California lawsuit alleging negligence by another person, plaintiffs typically must prove that the defendant acted in a way that violated a duty (reasonableness) owed to the plaintiff who was injured by an accident. In auto accident cases, this means violating the basic duty of care owed to everyone else on or near the roadways. As everyone knows, California has a lot of roadways!
California auto vs. bicycle accident lawsuits come down to facts specific to the individual case, and often the ability of the plaintiff to prove negligence through eyewitness testimony or other evidence that is made available. In auto accident cases, however, behaviors which constitute traffic violations can constitute "negligence per se." This means that if a driver was cited for a violation such as speeding at the time of the accident, evidence of the speeding violation counts as evidence of negligence. You do not have prove anything further - the mere fact of the ordinance or statutory violation constitutes the breach of duty to the injured party. The burden then shifts to the defendant to prove that he or she did not cause the plaintiff's injuries. This analysis is true of both California auto and bicycle (and pedestrian) accident cases.