Quoting from the Massachusetts Driver's Manual, chapter 4 (which you may find here: http://www.mass.gov/rmv/dmanual/chapter4.pdf):
"Steady Red -- A steady red light means “stop.” Do not go until the light turns green. You may make a right turn on a red light only after coming to a complete stop, then yielding to pedestrians or other vehicles in your path. You may not turn on red if a NO TURN ON RED sign is posted."
"Steady Yellow -- A steady yellow light means the traffic signal is changing from green to red. You must stop if it is safe to do so. If you are already stopped at an intersection or a stop line, you may not proceed."
"Steady Green -- A steady green light means “go,” but only after you have yielded to other vehicles, bicycles, or pedestrians in the road. If you are crossing an intersection, make sure you have enough room to make it completely through. Never block an intersection. You may make a turn as long as you have enough space to complete the turn and avoid creating a hazard. Look out for drivers who are not obeying traffic signals or are racing through intersections."
In case you missed them, let me pull out two important sentences: "Never block an intersection." And: "You must stop [on yellow] if it is safe to do so." Pulling into the middle of an intersection and stopping is "blocking an intersection". Turning left on a yellow is running a yellow light. I live, work, and walk in Boston, and I wish to fuck that Boston and would implement a "$100 and 2 Points" rule for these violations like New York City so people like you would stop nearly killing me every damn day.