Mass. Gen. Laws ch. 89 § 1
When persons traveling with vehicles meet on a way, each shall reasonably drive his vehicle to the right of the middle of the traveled part of such way, so that the vehicles may pass without interference, except that the department of highways may modify such restriction by pavement markings on state highways, on ways leading thereto and on all main highways between cities and towns. The department may by permit, revocable upon notice, authorize cities and towns to modify such restriction by pavement markings. All markings shall be in accordance with accepted standards of engineering practice, as provided in section two of chapter eighty-five.
The provisions of this section shall not be construed as prohibiting a vehicle from crossing a solid center pavement marking line or lines in making a left turn into or from a private way.
Mass. Gen. Laws ch. 89, § 1