The invention relates to a transmission for a boarding system for a rail vehicle, in which the transmission comprises a linearly movable drive shaft for an element of the boarding system, the drive shaft comprising a straight drive region and a curved locking region adjacent thereto, a drive wheel arranged at a distance from the drive shaft, a step-up gear that can move on a circular path around the drive wheel and is coupled to the drive wheel and the drive shaft, and an abutment device for defining a range of movement of the step-up gear between a drive position in the drive region and a locking position in the locking region.