Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 89, § 2

Except as herein otherwise provided, the driver of a vehicle passing another vehicle traveling in the same direction shall drive a safe distance to the left of such other vehicle and shall not return to the right until safely clear of the overtaken vehicle; and, if the way is of sufficient width for the two vehicles to pass, the driver of the leading one shall not unnecessarily obstruct the other. If it is not possible to overtake a bicycle or other vehicle at a safe distance in the same lane, the overtaking vehicle shall use all or part of an adjacent lane if it is safe to do so or wait for a safe opportunity to overtake. Except when overtaking and passing on the right is permitted, the driver of an overtaken vehicle shall give way to the right in favor of the overtaking vehicle on visible signal and shall not increase the speed of his vehicle until completely passed by the overtaking vehicle.

Except as herein otherwise provided, the driver of a vehicle passing another vehicle traveling in the same direction shall drive a safe distance to the left of such other vehicle and shall not return to the right until safely clear of the overtaken vehicle; and, if the way is of sufficient width for the two vehicles to pass, the driver of the leading one shall not unnecessarily obstruct the other. If it is not possible to overtake a vulnerable user, as defined in section 1 of chapter 90, or other vehicle at a safe distance in the same lane, the overtaking vehicle shall use all or part of an adjacent lane, crossing the centerline if necessary, when it is safe to do so and while adhering to the roadway speed limit. Except when overtaking and passing on the right is permitted, the driver of an overtaken vehicle shall give way to the right in favor of the overtaking vehicle on visible signal and shall not increase the speed of his vehicle until completely passed by the overtaking vehicle.

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 or 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.