A drive system for an entry/exit facility with at least one pivotably and/or slidably mounted door, ramp, tread or the like of a passenger transport vehicle, the system including at least one actuator or drive motor and a mechanical system driven by it and/or a gear unit for effecting the pivoting or sliding movement of the door, ramp, tread or the like, with an absolute value encoder for acquiring a momentary position during the pivoting or sliding movement, where an evaluation unit is configured to compare the momentary position with at least one reference position stored in a non-volatile memory of the evaluation unit in order to generate an output signal dependent thereon, and the absolute value encoder is flange-connected to a pin that fixes the pivoting movement of the door, ramp, tread or the like, and the gear unit includes a first reduction gear unit, a second reduction gear unit, and a controllable coupling is provided between the reduction gear units.