Boarding system, having sliding footstep and active seal

A boarding system for a passenger transport vehicle comprising:

• a door portal via which a floor of a passenger space of the vehicle is accessible,
• a door leaf with which a predominant area of a door opening can be closed,
• a step with a step tread surface, which is arranged below the floor in the vertical direction and, in the horizontal direction, extends from the door opening to a vertical surface connecting the step tread surface and the floor,
• wherein
• an extendable sliding tread, which is arranged below the door leaf in the area of the door portal and which has a horizontally oriented tread surface and, at an end facing towards the door leaf, a vertically oriented front wall, wherein
• the front wall reaches almost to the step tread surface,
• in a retracted end position of the sliding tread, the tread surface is completely underneath the floor,
• in an intermediate position of the sliding tread, the front wall is aligned with the closed door leaf,
• in an extended position of the sliding tread, the front wall is arranged outside the vehicle,
• wherein the boarding system has a movable sealing member which, in the intermediate position of the sliding tread, forms a seal against an adjacent passive sealing surface.