Every person operating a bicycle upon a way, as defined in section one of chapter ninety, shall have the right to use all public ways in the commonwealth except limited access or express state highways where signs specifically prohibiting bicycles have been posted, and shall be subject to the traffic laws and regulations of the commonwealth and the special regulations contained in this section, except that (1) the bicycle operator may keep to the right when passing a motor vehicle which is moving in the travel lane of the way...

Massachusetts law is very unusual in giving bicyclists blanket permission to overtake moving motor vehicles on the right, a special provision which does not apply to other drivers. Note, however, that this provision does not give bicyclists the right to overtake stationary vehicles, or anything except motor vehicles. So under this law, a bicyclist does not have blanket permission to overtake a horse-drawn carriage or another bicyclist on the right. Some implications of this law are examined in another Web page on this site, concerning an advanced stop line in Cambridge, Massachusetts.

The more restrictive wording about passing on the right which applies to all drivers    reads

Ch. 89 § 2. Passing vehicle traveling in same direction

...The driver of a vehicle may, if the roadway is free from obstruction and of sufficient width for two or more lines of moving vehicles, overtake and pass upon the right of another vehicle when the vehicle overtaken is (a) making of about to make a left turn, (b) upon a one-way street, or (c) upon any roadway on which traffic is restricted to one direction of movement.

Most other states have a different wording based on the Uniform Vehicle Code, and which applies to bicyclists as it does to all other drivers

11-304--When passing on the right is permitted

(a) The driver of a vehicle may overtake and pass upon the right of another vehicle only under the following conditions:

1. When the vehicle overtaken is making or about to make a left turn:

2. Upon a roadway with unobstructed pavement of sufficient width for two of more lines of vehicles moving lawfully in the direction being traveled by the overtaking vehicle.

(b) The driver of a vehicle may overtake and pass another vehicle upon the right only under conditions permitting such movement in safety. Such movement shall not be made by driving off the roadway.

The Uniform Vehicle Code wording permits overtaking moving OR stationary vehicles on the right when there is more than one lane for the same direction, but the antiquated Massachusetts wording (which hasn't been revised since before there were many such roads), does not.

But the most important part of the Uniform Vehicle Code wording is the last part, "only under conditions permitting such movement in safety." Under this provision, you pass on the right at your own risk. If you succeed in doing it without anyone's crashing or having to take evasive action, you are within the law. Otherwise, you are at fault.

This wording embodies wisdom, because the conditions under which overtaking on the right is safe can not be simply and clearly described. In my opinion, the Massachusetts law is faulty in that it lacks this wording.

But even if the law doesn't say so, you still pass on the right at your own considerable risk . Passing on the right is inherently hazardous because

1) it places you where drivers and pedestrians do not expect you;

2) you are in the right rear blindspot of drivers who may be about to turn right (or of passengers who may be about to open a door in front of you). There have been bicyclist fatalities in Cambridge and Boston withinin the past few of years (1999-2001) when vehicles turned right across the bicyclist's line of travel. Overtaking a long truck or bus on the right is extremely hazardous.

3) The vehicle you are overtaking can hide you from pedestrians and drivers crossing in front of it (and hide them from you).

And in that connection, there is another provision of Massachusetts law which often affects the legality of overtaking on the right. Chapter 89 § 11 includes the wording:

No driver of a vehicle shall pass any other vehicle which has stopped at a marked crosswalk to permit a pedestrian to cross, nor shall any such operator enter a marked crosswalk until there is a sufficient space beyond the crosswalk to accommodate the vehicle he is operating notwithstanding that a traffic control signal may indicate that vehicles may proceed.

This prohibits overtaking on either side when there is, or might be, a pedestrian in a crosswalk. My understanding is that a bicyclist who collided a pedestrian in Boston a couple of years ago, in a case which got heavy publicity, was violating this rule while overtkaing on the right. The bicyclist had the green light, but the vehicle to the bicyclist's left, which also had the green light, had not started moving because of the pedestrian in the crosswalk. The bicyclist and pedestrian did not see each in time other because of the vehicle in between them.

Also note that any pedestrian who has entered a crosswalk legally has the right to finish crossing in safety. The recently-introduced "countdown" pedestrian signals do NOT mean "you have 15, 14, 13... seconds to get across, and after that, drivers have a license to run you over" -- though the signals certainly do convey that false impression. Well, maybe: see Ed Kearney's comments on another page. The pedestrian in the infamous Boston case may or may not have entered the crosswalk legally, but regardless of this, the bicyclist was in violation of Chapter 89, Section 11, and was probably also in violation of Chapter 85, Section 11B because the vehicle was not moving, and because of failure to use a headlight while riding at night.