A system to access a passenger compartment, said system having a door hinged to a chassis frame by a first horizontal articulated joint and forming an inclined ramp, wherein said system comprises an actuator to move said door, linked to said door and said chassis frame, a step plate at least partially covering the outside of said door and hinged to said chassis frame by a second articulated joint parallel to said first articulated joint and with a hinge pin offset to the first articulated joint, said step plate linked to said door by a drive element connected to said door by a third articulated joint and to said step plate by a fourth articulated joint, the pins of said first through fourth articulated joints being parallel to one another and form the four summits of a parallelogram deformable between open and closed positions of said door.