Md. Code, Transportation § 11–173

(a) “Type I school vehicle” means a school vehicle that:

(1) Is designed and constructed to carry passengers;

(2) Is either of the body-on-chassis type construction or integral type construction; and

(3) Has a gross vehicle weight of more than 15,000 pounds and provides a minimum of 13 inches of seating space per passenger.

(b) “Type I school vehicle” does not include any bus operated by a common carrier under the jurisdiction of a State, regional, or federal regulatory agency or operated by the agency itself.