Abstract: A method of smoothing the outer surfaces of sliding doors wherein, after a doorway is closed with a sliding door, a wall member is projected outwardly, the outer wall member having an outer surface of a size and shape which is nearly the same as those of the doorway, such that the surface of the outer wall member is flush with the surface of the structure.

Abstract: A vehicle body able to withstand fluctuating external pressure while providing ample space for the passengers, by having a multiplicity of substantially square, first frames each having reinforced portions on two upper corners thereof, provided by rounding inner surfaces of the two upper corners, and a multiplicity of substantially square, second frames having reinforced portions on two lower corners thereof provided by rounding inner surfaces of the two lower corners. They are arranged alternately over the length of the vehicle body, and are connected together by longitudinal structural members. A shell plate is attached to the substantially square frames at their outer surfaces, to provide a substantially square vehicle body.