Many people do not realize that it is perfectly legal to take a left turn on a red light from a two-way street when you are turning onto a one-way street. This kind of turn is specifically authorized by statute.
RCW 46.61.055 (3)(a) states as follows:
However, the vehicle operators facing a steady circular red signal may, after stopping proceed to make a right turn from a one-way or two-way street into a two-way street or into a one-way street carrying traffic in the direction of the right turn; or a left turn from a one-way or two-way street into a one-way street carrying traffic in the direction of the left turn; unless a sign posted by competent authority prohibits such movement.
Our Seattle traffic ticket attorneys almost never see people utilizing this little known but extremely handy traffic law. It seems that many people who are aware of the law are actually worried that an officer will not know the law and will pull them over when they make that left turn.