Passenger Seats. The minimum clearance of all aisles, including the aisle or passageway between seats leading to the emergency door, shall be 12 inches. The forward-most seat on the right side of the vehicle shall be located so as not to interfere with the operator's vision and may not be farther forward than the rear of the operator's seat when adjusted to its rearmost position. The backs of seats of similar size shall be of the same width at the top, of the same height from the floor, and shall slant at the same angle with the floor. Seats shall be forward facing and shall be securely fastened with bolts and nuts to supporting parts of the vehicle. Each seat leg shall be fastened with a minimum of two bolts and nuts. Portable seats may not be used. Aisle supports of seat backs shall be slanted away from the aisle sufficiently to give an aisle clearance of 15 inches at the tops of the seat backs. As of January 1, 2014, all vehicles procured for use in this State shall be constructed with materials that enable it to meet all the criteria of the school bus seat upholstery fire block test established by the National School Transportation Specifications and Procedures adopted at the most recent National Congress on School Transportation. Seat cushions shall be fastened to the seat structure. Seat covering shall be of minimum 42-ounce or approved equal material. Operator's Seat. The minimum distance between the steering wheel and the backrest of the operator's seat is 11 inches. The operator's seat shall: Be rigidly positioned; Have fore and aft adjustment of not less than 4 inches, without the use of tools or other devices; and Be fastened to the floor with bolts, nuts, and washers or flanged-head nuts. Crash Barriers. Crash barriers shall be located on both sides of the aisle in front of the most forward facing seat. On vehicles with the engine inside the front of the body, the minimum distance between the barrier at the rear of the entrance stepwell and the engine cover shall be 14 inches at floor level. As of January 1, 2014, all vehicles procured for use in this State shall be constructed with materials that enable it to meet all the criteria of the school bus seat upholstery fire block test established by the National School Transportation Specifications and Procedures adopted at the most recent National Congress on School Transportation. Sun Visor. An interior adjustable sun visor supported by two brackets not less than 5 inches wide and 15 inches long shall be installed so that it can be turned up to prevent being a hazard when not in use. Steering Wheel. The steering wheel circumference shall have at least 2 inches of clearance at all points. Speakers. Ceiling or side mounted speakers shall be flush mounted.