A method for loading a road semi-trailer on a pocket wagon comprising a railway structure with a receptacle and a removable assembly for loading/unloading a road semi-trailer comprising: - a removable shell, designed to be removably engaged in the receptacle of the railway structure, which comprises a bottom wall, two side walls and two longitudinal beams located in the upper portion above the side walls, with the assembly forming a loading pocket for the semi-trailer, and which also comprises first immobilization elements and mechanical interfaces able to cooperate with the gripping elements of a handling machine; and - a locking device, which comprises second immobilization elements which cooperate with the first immobilization elements to ensure the removable attachment of the locking device on the removable shell; and a coupling seat for the semi-trailer coupling pin to anchor the semi-trailer to the removable shell; this method including the step consisting of: - grasping the removable shell by engaging the gripping means of a handling machine in the mechanical interfaces of the removable shell, and, using the handling machine, raising the removable shell and placing it out of the railway structure receptacle; this method being characterized in that it includes the following steps: - fitting the locking device on the semi-trailer which was previously left by its road tractor, by engaging the semi-trailer coupling pin into the coupling seat of the locking device; - loading the semi-trailer equipped with the locking device onto the removable shell using a handling tractor, running it forward or in reverse onto the bottom wall of the removable shell, between the side walls and the longitudinal beams; - using the handling tractor, placing the locking device on the removable shell, in a position allowing the second immobilization elements to cooperate with the first immobilization elements; - releasing the handling tractor and moving it away from the removable assembly; - grasping the loaded removable assembly by engaging the gripping means of the handling machine in the mechanical interfaces of the removable shell and lifting the loaded removable assembly; - using the handling machine, placing the loaded removable assembly onto the railway structure, by engaging the removable shell in the receptacle of the railway structure. - a removable shell, designed to be removably engaged in the receptacle of the railway structure, which comprises a bottom wall, two side walls and two longitudinal beams located in the upper portion above the side walls, with the assembly forming a loading pocket for the semi-trailer, and which also comprises first immobilization elements and mechanical interfaces able to cooperate with the gripping elements of a handling machine; and - a locking device, which comprises second immobilization elements which cooperate with the first immobilization elements to ensure the removable attachment of the locking device on the removable shell; and a coupling seat for the semi-trailer coupling pin to anchor the semi-trailer to the removable shell; - grasping the removable shell by engaging the gripping means of a handling machine in the mechanical interfaces of the removable shell, and, using the handling machine, raising the removable shell and placing it out of the railway structure receptacle; - fitting the locking device on the semi-trailer which was previously left by its road tractor, by engaging the semi-trailer coupling pin into the coupling seat of the locking device; - loading the semi-trailer equipped with the locking device onto the removable shell using a handling tractor, running it forward or in reverse onto the bottom wall of the removable shell, between the side walls and the longitudinal beams; - using the handling tractor, placing the locking device on the removable shell, in a position allowing the second immobilization elements to cooperate with the first immobilization elements; - releasing the handling tractor and moving it away from the removable assembly; - grasping the loaded removable assembly by engaging the gripping means of the handling machine in the mechanical interfaces of the removable shell and lifting the loaded removable assembly; - using the handling machine, placing the loaded removable assembly onto the railway structure, by engaging the removable shell in the receptacle of the railway structure.