Sliding step assembly for a vehicle or a rail vehicle for bridging a gap between the vehicle or rail vehicle and a platform or similar, having a) a sliding step cassette which can be fixed to an undercarriage of the vehicle or rail vehicle, with a cassette opening, b) a sliding step guided on the sliding step cassette so as to be movable along a sliding step displacement path between a retracted position and at least one fully extended position, the sliding step being accommodated in the sliding step cassette in the retracted position and being movable by means of a drive device through the cassette opening from the retracted position into the at least one fully extended position, and from the at least one fully extended position into the retracted position, c) at least one closure element mounted on the sliding step, which closes the cassette opening when the sliding step is in the retracted position, characterised in that d) at least one obstacle detection means is provided, having a touch-sensitive element, which is designed in such a way that, upon contact of the touch-sensitive element with an obstacle during the extension movement of the sliding step from the retracted position into the at least one fully extended position, a critical position of the sliding step in relation to the obstacle is detected and, in the event of such a detection, a detection signal is generated, wherein e) the closure element and the touch-sensitive element are formed together by a cover flap movably guided by means of a guide device (22, 24, 26) in such a way that the position of the cover flap relative to the sliding step and / or the sliding step cassette is dependent on the position of the sliding step on the sliding path, wherein f) the guide device (22, 24, 26) is designed so that, as a result of the sliding step being moved into the retracted position, the cover flap is brought into a closed position, in which the cover flap closes the cassette opening and, as a result of movement from the retracted position in the direction of the at least one fully extended position, the cover flap assumes a detection position, in which at least a portion of the cover flap lies within a detection area, in order to make contact with any obstacle that may be present in the detection area and then, in the event of such contact with the obstacle, to generate the detection signal. a) a sliding step cassette which can be fixed to an undercarriage of the vehicle or rail vehicle, with a cassette opening, b) a sliding step guided on the sliding step cassette so as to be movable along a sliding step displacement path between a retracted position and at least one fully extended position, the sliding step being accommodated in the sliding step cassette in the retracted position and being movable by means of a drive device through the cassette opening from the retracted position into the at least one fully extended position, and from the at least one fully extended position into the retracted position, c) at least one closure element mounted on the sliding step, which closes the cassette opening when the sliding step is in the retracted position, characterised in that d) at least one obstacle detection means is provided, having a touch-sensitive element, which is designed in such a way that, upon contact of the touch-sensitive element with an obstacle during the extension movement of the sliding step from the retracted position into the at least one fully extended position, a critical position of the sliding step in relation to the obstacle is detected and, in the event of such a detection, a detection signal is generated, wherein e) the closure element and the touch-sensitive element are formed together by a cover flap movably guided by means of a guide device (22, 24, 26) in such a way that the position of the cover flap relative to the sliding step and / or the sliding step cassette is dependent on the position of the sliding step on the sliding path, wherein f) the guide device (22, 24, 26) is designed so that, as a result of the sliding step being moved into the retracted position, the cover flap is brought into a closed position, in which the cover flap closes the cassette opening and, as a result of movement from the retracted position in the direction of the at least one fully extended position, the cover flap assumes a detection position, in which at least a portion of the cover flap lies within a detection area, in order to make contact with any obstacle that may be present in the detection area and then, in the event of such contact with the obstacle, to generate the detection signal.