The invention relates to a transitional coupling (15; 53; 83) for coupling the coupling devices (7, 12; 37, 42; 67, 72) of two vehicles (2, 3; 32, 33; 62, 63) having air conduits (5, 10; 35, 40; 65, 70), having a first connecting device (16; 52; 82) for detachably connecting the transitional coupling to a first (7; 37; 67) of the coupling devices, having a second connecting device (18; 54; 84) for detachably connecting the transitional coupling to a second (12; 42; 72) of the coupling devices, having a coupling carrier (20; 55; 85) for connecting the first connecting device (16; 52; 82) to the second connecting device (18; 54; 84), and having a coupling conduit (21; 56; 86) for connecting the air conduits (5, 10; 35, 40; 65, 70) of the two vehicles. In order to improve the interoperability of the transitional coupling (15; 53; 83) and of the vehicles (2, 3; 32, 33; 62, 63) of a vehicle group (1; 31; 61), said vehicles being coupled by means of such a transitional coupling, an air preparation device (23; 23a; 23b) held by the coupling carrier (20; 55; 85) and having an air preparation unit (24.1) is provided, wherein the one air preparation unit (24.1) is arranged in the airflow path of the one coupling conduit (21; 56; 86).