No person shall drive a bus and a motor carrier shall not require or permit a person to drive a bus unless—

(a) All standees on the bus are rearward of the standee line or other means prescribed in § 393.90 of this subchapter;

(b) All aisle seats in the bus conform to the requirements of § 393.91 of this subchapter; and

(c) Baggage or freight on the bus is stowed and secured in a manner which assures—

(1) Unrestricted freedom of movement to the driver and his proper operation of the bus;

(2) Unobstructed access to all exits by any occupant of the bus; and

(3) Protection of occupants of the bus against injury resulting from the falling or displacement of articles transported in the bus.