This assembly firstly comprises a framework fastened on the body of a vehicle, a swiveling floor intended for the forward motion of travelers, in particular, persons with reduced mobility, and an intermediate device, located below the surface for forward motion. The intermediate device and the swiveling floor are able to swivel in relation to the framework in a mutually independent manner. This assembly moreover comprises a sliding system that is movable in translation in relation to the intermediate device between a stowed position and a deployed position, in which this sliding system forms, together with the surface for forward motion, a ramp extending through a lateral opening of the framework.