Mass. Gen. Laws ch. 160, § 190

Every railroad corporation having a terminus in Boston, except the Boston, Revere Beach and Lynn Railroad Company, shall sell a commutation ticket good for not more than twelve rides between Boston and each station on its lines within fifteen miles of its terminal station in Boston. The said tickets, before issuance, shall be subject to approval by the department both as to the rate of fare and the conditions named therein. So far as is practicable, the rates of fare on all roads for like distances from their terminal stations shall be equal.