fig1 shows a rear module 1 which is constituted in this embodiment by assembling together a central portion 1 a and two side portions 1 b . the central portion 1 a and the side portions 1 b in the embodiment described are all made of reinforced thermoplastic material . the thermoplastic material can be reinforced using glass fiber cloth and / or metal inserts , for example . the central portion 1 a is assembled to the side portions 1 b by fastening means that can easily be undone , possibly with adjustment for docking tolerances . in the embodiment described , each side portion 1 b includes a wall 12 that bears against a wall 13 of the central portion 1 a , these walls 12 and 13 being assembled together by means of bolts 30 co - operating with nuts 31 and washers 32 , as shown in fig2 . the walls 12 and 13 support respective stiffening ribs 33 and 34 . in a variant , it is possible to use other fastener means suitable for enabling the central portion 1 a or one of the side portions 1 b to be replaced easily , in the event of it being damaged in an accident . as general rule , the rear module 1 is arranged so as to enable it to be secured to the side rails l and to the rear side portions of the vehicle body c . in the example described , the rear module 1 is secured to the side rails l without using welding , thus facilitating replacement , e . g . by using bolts . a variety of vehicle styles can be made using the same platform , by fitting rear modules of different shapes thereto . advantageously , as shown , the side portions 1 b include housings 2 for receiving or constituting parts of the signaling light inserts ( not shown ). the rear module 1 forms the rear skirt of the vehicle body and replaces the cross - member of conventional vehicle platforms of the kind described in above - cited french patent application no . fr - b - 2 773 132 , for example . the rear module is arranged to receive both an impact - absorbing beam 3 for absorbing the energy of an impact , and also a rear shield 4 . advantageously , the rear module 1 includes cellular structures 5 ( as can be seen in fig1 ) having walls that extend substantially along the axes of the side rails l , for the purpose of transmitting the forces exerted by the beam 3 to the side rails l of the vehicle . the side portions 1 b are shaped in such a manner as to match the shapes of the rear side portions of the body c when the rear module 1 is fixed to the side rails l . in the embodiment described , the side portions 1 b are also arranged so as to be fixed to the rear side portions of the vehicle body c . in the embodiment of fig1 the floor 6 is fixed on the side rails l before the rear module 1 is put into place . the floor 6 has two side portions 6 a that rest on the side rails l and a central depression 6 b constituting a housing suitable for receiving the spare wheel , or a space - saver spare wheel , for example . the central portion 1 a has a wall 7 which finishes off the depression 6 b when the rear module 1 is in place . the wall 7 can be formed integrally with the remainder of the module 1 or it can be fitted thereto . the wall 7 then forms an extender to the floor 6 in the meaning of the present invention . the central portion 1 a can have hinges 8 represented highly diagrammatically by dashed lines in fig1 enabling a door ( not shown ) to be assembled to the module 1 so as to be capable of pivoting about its bottom edge . two ways of assembling a bumper to a rear module are described below with reference to fig3 and 4 . fig3 shows a rear module 15 assembled to a shield 4 ′ constituting an element of bodywork . the module 15 has a folded - back portion 17 presenting a wall 16 against which there bears a folded - back portion 18 made at the top of the shield 4 ′. the shield 4 ′ is fixed to the rear module 15 by means of rivets 20 placed through the folded - back portion 18 and the wall 16 . fig4 shows a variant way of assembling a module 15 ′ to a shield 4 ″. the module 15 ′ has a rim 22 that is directed towards the outside of the vehicle and that forms a bearing surface for mounting a folded - back portion 21 formed at the top of the shield 4 ″. the shield 4 ″ is secured to the module 15 ′ by means of rivets 20 as in the assembly described above . the module 15 ′ also has a rib 25 supporting a sealing gasket 26 against which the tailgate 40 of the can come to bear . the shield 4 ″ covers an impact - absorbing beam 3 which is secured to the module 15 ′ by fastenings that are not shown . various items of equipment , in particular the shield , can be secured to the rear module by any fastening means other than rivets , e . g . bolts . the various elements of the rear module , in particular its central portion and one of its side portions , or an element fixed to one of the central and side portions can be held together by fastening means that accommodate docking tolerances . by way of example , fig5 shows an assembly that enables such docking tolerances to be adjusted , which assembly has a bolt 30 engaged in an oblong hole 38 and co - operating with a nut 31 . the presence of the oblong hole makes it possible to adjust docking tolerances e between two elements that are assembled together . by way of example , fig6 shows a rear module 1 ′ which differs from the above - described rear module 1 by the fact that it is delivered to the manufacturer in a preassembled state together with a floor 6 ′. in a variant , the floor 6 ′ can be made integrally with the central portion of the rear module 1 ′ by molding thermoplastic or thermosetting material . without going beyond the ambit of the present invention , it is possible to preassemble a large number of items of equipment and / or elements of bodywork onto the module that is delivered to the manufacturer . thus , for example , the rear floor can have preassembled thereto trim for the trunk or thermal screens and / or sound screens . the module 1 ′ can also be fitted with an element 29 for locking a door , shown in dashed lines in fig6 . fig7 shows a rear module 1 ″ comprising a central portion 1 ″ a and two side portions 1 ″ b , the central portion 1 ″ a being designed to be secured to the side rails l and to a floor 6 ″, which floor is preassembled in particular with the trim for the wheel arches 10 and the hatches 11 for storing accessories . fig7 also shows signaling devices ( i . e ., light inserts ) 42 and elements 40 of the system for filling the fuel tank . the rear module 1 ″ is designed to receive an impact - absorber beam 3 and a rear shield 4 .