Mass. Gen. Laws ch. 161B § 9A
If in any year the commonwealth shall be called upon to pay any amount on account of the net cost of service of the Cape Cod Regional Transit Authority, the total amount of such net cost of service may be assessed in whole or in part upon the cities and towns which are members of such Authority on the basis of the total passenger miles and the number of trips attributable to the residents of cities and towns within said Authority. Any such assessment formula shall be subject to the approval of the secretary and the advisory board of the Authority.
Such determination shall be made by said Authority in accordance with sound accounting practice and guidelines developed in consultation with the department. Amounts assessed under this section shall be the most recently audited regional transit authority assessment available on January 1 of each year and shall be used to calculate the upcoming fiscal year's estimated cherry sheet assessments.
Mass. Gen. Laws ch. 161B, § 9A