There are many things drivers, pedestrians and cyclists do that are not in accordance with the official rules but are expected and accepted. If you don't expect and accept your local variation of whatever these exceptions are you are going to have a very bad time. There is a predictable pattern to how traffic works. Being caught up on the letter of the law will results in you poorly communicating with all the other traffic around you which increases the frequency of conflicts. They way you walk or drive in Boston is different than the way you walk or drive in SF and neither of them adheres strictly to the official rules and markings.