Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 82, § 6

They may make such changes between the termini of the highway described in the petition, relative to the direction and course of such highway or to the alteration, specific repair or discontinuance thereof, as in their opinion the public convenience requires, and, in connection with the laying out, alteration or relocation thereof, may establish a building line not more than forty feet distant from the exterior line of such highway, extending for such distance from points where such highway joins an intersecting way, as defined in section one of chapter ninety, as may be necessary to insure the safety of the public, and thereafter no structures shall be erected or maintained between such building line and such highway except steps, windows, porticos, other usual projections appurtenant to the front wall of a building, embankments, walls, fences and gates, to the extent prescribed by the order establishing such building line. A building line so established may be discontinued in the manner provided for the discontinuance of a highway.