When used as a school bus, a mass transit pupil transportation bus shall provide designated seating positions of safe design and construction for all school children. A school child may not be carried for which a safe designated seating position is not available.
67 Pa. Code § 171.139
The provisions of this §171.139 issued under the Vehicle Code, 75 Pa.C.S. §§ 4103, 4551-4553 and 6103.