The step risers shall be approximately equal in height with the upper riser not more than 15 inches in height. The surface of steps shall be completely covered with a nonskid material having 1-1/2 inch white nosing, fire-resistant, nonskid wear-resistant, and rubber step treads, which shall have a minimum overall thickness of 0.1875 inch. The steps shall be enclosed to prevent accumulation of ice and snow and may not protrude beyond the width of the body. The step well shall be illuminated by at least one lamp providing white light actuated automatically by the opening of the door. The lower step shall be not less than 12 inches and not more than 16 inches above the level on which the unloaded bus rests.