The Chief of Police is authorized, and as to those signs and signals required hereunder it shall be his duty, to place and maintain or cause to be placed and maintained all official traffic signs, signals, markings and safety zones. All signs, signals, markings and safety zones shall conform to the standards as prescribed by the Department of Public Works of the Commonwealth.
Colors and arrow indications in traffic control signals shall have the commands ascribed to them in this section, and no other meanings, and every driver of a vehicle or other conveyance shall comply therewith except when otherwise directed by an officer.
A. 
Red. While the red lens is illuminated, no driver of a vehicle facing the signal shall enter the intersection; provided, however, that if a right or left green arrow lens is illuminated at the same time, a driver may enter the intersection to make the turn permitted by the arrow.
B. 
Yellow. While the yellow lens is illuminated, any waiting driver of a vehicle shall remain standing until the green lens is illuminated; any driver of a vehicle approaching the intersection, who can stop such vehicle with safety before reaching the intersection, or a marked stop line, shall stop at such point.
C. 
Green. While the green lens is illuminated, any driver of a vehicle facing the signal shall proceed, subject to the safety of those who might have been in the intersection at the time the lens was illuminated. Drivers of vehicles making a right or left turn shall yield the right-of-way to pedestrians crossing with the flow of traffic.
D. 
Red and yellow. While the red and yellow lenses are illuminated simultaneously, no driver of a vehicle shall enter the intersection, and during such time the intersection is reserved for the exclusive use of pedestrians.
E. 
Right, left and vertical green arrows. When a right green arrow is illuminated, drivers facing the signal may turn right; when a left green arrow is illuminated, drivers facing the signal may turn left. When a vertical green arrow is illuminated, drivers facing the signal may go straight ahead. When a green arrow is exhibited together with a red or yellow lens, drivers may enter the intersection to make the movements permitted by the arrow but shall yield the right-of-way to vehicles and pedestrians proceeding them from another direction on a green indication.
F. 
Flashing red. The red lens when illuminated with rapid intermittent flashes shall require drivers to come to a complete stop before entering the intersection, and the right to proceed within a crosswalk shall then be governed by the provisions of MGL c. 89, § 8.
G. 
Flashing yellow. The yellow lens when illuminated with rapid intermittent flashes shall indicate the presence of danger and shall permit drivers to proceed only with caution.
It shall be unlawful for any person to place, maintain or to display any unofficial sign, signal, device or marking which purports to be or is an imitation of or resembles an official traffic sign, signal, device or marking or which attempts to direct the movement of traffic.
It shall be unlawful for any person to willfully deface, injure, move, obstruct or interfere with any official traffic sign, signal, device or marking.
At any injunction or crossing of ways where the roadway grades have been separated and where the ways are connected by ramps and at any intersection of ways in which there are traffic islands, drivers of vehicles shall proceed only as indicated by official signs, signals or markings.
It shall be unlawful for any operator of a motor vehicle to disobey the instructions on any traffic control signal, traffic sign or markings on the street placed in accordance with the provisions of this chapter unless otherwise directed by a police officer.