Mass. Gen. Laws ch. 160 § 220
Whoever, without right rides or attempts to ride upon a locomotive engine, tender, freight car, caboose, other conveyance or passenger train upon a railroad or upon the trains of the Massachusetts Bay Transportation Authority commuter rail other than as a fare paying passenger, or employee, shall be punished by a fine of not more than five hundred dollars or imprisonment for not more than six months. A sheriff, deputy sheriff, constable, police officer, railroad police officer, or officer appointed with the powers of a railroad police officer, upon view of such offense, may, without a warrant, arrest the offender and make complaint against him therefor.
This section shall not apply to railroad employees while in the discharge of their duties.
Mass. Gen. Laws ch. 160, § 220