Many people think that traveling the speed limit is the best speed to drive when driving on the freeway or city streets. However, if you get involved in an auto accident, your speed will be in an issue. Driving the "speed limit" is not a defense to driving too fast. Technically, you can drive the speed limit and still be guilty of driving too fast. California's basic speed law (Vehicle Code Section 22350) does not say anything about the speed limit. California's basic speed law says that you must drive at the speed that is reasonable for the circumstances. Therefore, even if the speed limit is 55 mph, that does not mean you can drive 55 mph if there is traffic or stoppage in other lanes etc. When it comes down to it, California's driving law requires a driver to be "reasonable" which doesn't necessarily mean driving the speed limit.
Back when I was a defense lawyer (defending personal injury cases for a major insurance company), I once had a case once where my client mistakenly turned left into oncoming traffic. There were three lanes in the opposite direction and cars in the #1 and #2 lanes stopped for him. The other party was driving the speed limit (35 mph) in the #3 lane and hit him while he was turning. While my client should not have turned, we did get the jury to find the other vehicle's driving to be 30% at fault for driving too fast. We argued that since cars were stopped in the #1 and #2 lanes, she should have realized something was going on and driving the speed limit could not be used as an excuse. Arguably, we had a steep hill to climb with such an argument, but the argument worked in that case.