Mass. Gen. Laws ch. 90, § 7C

The registrar, after a public hearing, may make, alter, rescind or add to rules and regulations establishing minimum standards for construction and equipment of school buses, which shall apply to all school buses without regard to any prior date when they were operated as such. A violation of any rule or regulation made under this section shall be punished in the same manner as a violation of a rule or regulation made under section thirty-one. Such rules and regulations shall not apply to a motor vehicle operated by a holder of a certificate issued under section seven of chapter one hundred and fifty-nine A and a permit issued under section eight of said chapter.