Mass. Gen. Laws ch. 90 § 14
Every person operating a motor vehicle shall bring the vehicle and the motor propelling it immediately to a stop when approaching a cow, horse or other draft animal being led, ridden or driven, if such animal appears to be frightened and if the person in charge thereof shall signal so to do; and, if traveling in the opposite direction to that in which such animal is proceeding, said vehicle shall remain stationary so long as may be reasonable to allow such animal to pass; or, if traveling in the same direction, the person operating shall use reasonable caution in thereafter passing such animal. In passing a vulnerable user, the operator of a motor vehicle shall pass at a safe distance of not less than 4 feet and at a reasonable and proper speed. In approaching or passing a car of a street railway which has been stopped to allow passengers to alight from or board the same, the person operating a motor vehicle shall not drive such vehicle within eight feet of the running board or lowest step of the car then in use by passengers for the purpose of alighting or boarding, except by the express direction of a traffic officer or except at points where passengers are protected by safety zones. When approaching a vehicle which displays a sign bearing the words "SCHOOL BUS'' and which is equipped with front and rear alternating flashing red signal lamps which are flashing, as provided in section seven B, and which has been stopped to allow pupils to alight from or board the same, a person operating a motor vehicle or trackless trolley shall, except when approaching from the opposite direction on a divided highway, bring his vehicle or trackless trolley to a full stop before reaching said school bus and shall not thereafter proceed until the warning signals are deactivated, unless directed to the contrary by a police officer duly authorized to control the movement of traffic. Any person who violates the preceding sentence shall be punished by a fine of not less than $250; and for a second offense by a fine of not less than $500 nor more than $1,000; and for a third or subsequent offense by a fine of not less than $1,000 nor more than $2,000. A second conviction or third or subsequent conviction as set forth in the preceding sentence shall be reported forthwith by the court or magistrate to the registrar who shall revoke immediately the license or right to operate of the person so convicted and no appeal, motion for a new trial or exceptions, shall operate to stay the revocation of the license or right to operate; provided, however, that no license or right to operate shall be issued by the registrar to any person convicted of a second such offense until 6 months after the date of revocation following said conviction or to any person convicted of a third or subsequent such offense until 1 year after the date of revocation following said conviction; and provided, further, that if the prosecution against such person has terminated in his favor the registrar shall forthwith reinstate his license or right to operate. No person shall operate a motor vehicle within a distance of 100 feet behind a school bus. Every school bus shall have the words "keep back 100 feet'' prominently displayed on the back of the bus, in type large and dark enough so that the words are legible at a distance of 100 feet. Upon approaching a pedestrian who is upon the traveled part of any way and not upon a sidewalk, every person operating a motor vehicle shall slow down. The person operating a motor vehicle on any way or a curve or a corner in said way where his view is obstructed shall slow down and keep to the right and upon approaching any junction of said way with an intersecting way shall, before entering the same, slow down and keep to the right of the center line. When turning to the right, an operator shall do so in the lane of traffic nearest to the right-hand side of the roadway and as close as practicable to the right-hand curb or edge of roadway. No person operating a vehicle that overtakes and passes a bicyclist proceeding in the same direction shall make a right turn at an intersection or driveway unless the turn can be made at a safe distance from the bicyclist at a speed that is reasonable and proper. When approaching for a left turn on a two-way street, an operator shall do so in the lane of traffic to the right of and nearest to the center line of the roadway and the left turn shall be made by passing to the right of the center line of the entering way where it enters the intersection from his left. When turning to the left within an intersection or into an alley, private road or driveway an operator shall yield the right of way to any vehicle approaching from the opposite direction, including a bicycle on the right of the other approaching vehicles, which is within the intersection or so close thereto as to constitute an immediate hazard. It shall not be a defense for a motorist causing an accident with a bicycle that the bicycle was to the right of vehicular traffic. When approaching for a left turn on a one-way street, an operator shall do so in the lane of traffic nearest to the left-hand side of the roadway and as close as practicable to the left-hand curb or edge of roadway. No person shall open a door on a motor vehicle unless it is reasonably safe to do so without interfering with the movement of other traffic, including bicyclists and pedestrians. Whoever violates the preceding sentence shall be punished by a fine of not more than $100.
The department, on ways within their control and at the intersection of state highways, and other ways, the metropolitan district commission, on ways within their control and at the intersection of metropolitan district commission roadways, except state highways, and other ways, the traffic and parking commission of the city of Boston, the traffic commission or traffic director of any city or town having such a commission or director with authority to promulgate traffic rules, the city council of any other city, and the board of selectmen of any other town may provide for the placing of traffic control devices in accordance with department standards to indicate the course to be traveled by vehicles turning at such intersections. Such course may be other than as is prescribed by the requirements for lane usage set forth in this section.
The Massachusetts Department of Transportation shall erect and maintain signage along public ways necessary to notify operators of motor vehicles of the requirements for passing a vulnerable user from a safe distance as required by this section.
Such regulations and devices shall be, so far as applicable, subject to the provisions of section two of chapter eighty-five.
Mass. Gen. Laws ch. 90, § 14