California Motor Vehicle Code 21208
According to California Vehicle Code 21208, if your city has a lane dedicated specifically for bicycles, then all bike riders must use the bike lane. This law is meant to give riders a safe place to ride on busy city streets. Thousands of bicycle accidents occur each year on busy southern California streets, and many cities have dedicated bike lanes for those who wish to travel in a more environmentally friendly manner. There are exceptions to this, though, and it is important to know what those may be. If it is unsafe to ride inside the bike lane, for whatever reason, then riders should use common sense and ride where it will be the safest for them.
Drivers are not always courteous to bicyclists, and they sometimes ignore dedicated lanes. If there are cars illegally parked in the bike lane, then you should not ride in the lane until it is safe to do so. A little vigilance goes a long way in protecting yourself and others.
If you are an avid cyclist who can travel at high rates of speed, you may not want to risk other rider's safety by riding in the bicycle lane. One of the common exceptions to this law is for those who can safely ride at the same speed as cars and trucks. In that scenario, you don't have to ride in the dedicated bike lane. It would be incredibly unsafe to go whizzing past slower riders inside a tiny bicycle lane.
If you are leaving the bicycle lane for any reason, such as: passing other bikers, turning onto another street, or avoiding road hazards; you must signal your intentions to all moving vehicles before leaving the bicycle lane. Just because there is a dedicated bike lane, this does not give you an excuse to dart in front of passing motorists or other bikes.
Safety will always be the number one factor considered in any situation. If you ride outside the dedicated bike lane in an unsafe manner, you will most likely get a ticket for your actions. When in doubt, it's best to stay inside the dedicated bike lane.
By following this traffic law, and considering the safety of both yourself and others, the streets can be an enjoyable place for everyone using them.