A road transport vehicle (1; 40) comprising a chassis (2; 41) having a longitudinal axis, a carriage (11; 44) mounted so as to be translatable along the longitudinal axis of the chassis (2; 41) and having a front side and a rear side being respectively located on the front and rear sides of the chassis (2; 41), at least one member (18; 45) for translationally guiding the carriage (11; 44), and a load supporting structure (12; 43) connected to the carriage (11; 44) and having an vehicle front-side end region and a vehicle rear-side end region, the carriage (11; 44) being movable between a first, so-called transport position, in which the load supporting structure (12; 43) is carried by the chassis (2; 41), and a second position, in which the load supporting structure (12; 43) rests on the ground by its front-side and rear-side end regions, the one or more guiding members (18; 45) being movable between a substantially horizontal position and at least one tilted position in which it is tilted towards the back of the vehicle (1; 40) with its rear end in the vicinity of the ground, means for controlling the tilting motion of the one ore more guiding members (18; 45) and means for controlling the translational motion of the carriage (11; 44) being provided, characterised by the fact that: - the load supporting structure (12; 43) and the rear side of the carriage (11; 44) are connected by at least one rotary joint comprising, on one hand, a pivot pin carried by one of the carriage (11; 44) and the load supporting structure (12; 43), and, on the other hand, at least one hook carried by the other of the carriage (11; 44) and the load supporting structure (12; 43), the at least one hook having an opening in which said pivot pin is removably accommodated, the opening of the at least one hook thus providing an abutment surface allowing to make the carriage (11; 44) and the load supporting structure (12; 43) translationally integral with each other so that a translational motion of the carriage (11; 44) causes a translational motion of the load supporting structure (12; 43), and - means are provided, in the rear end region of the one or more guiding members (18; 45), for tilting the rear side of the carriage (11; 44) downwards with respect to the mean longitudinal axis of the or each guiding member (18; 44), so as to bring closer to the ground the one of the pivot pin and the at least one hook that is carried by the carriage (11; 44), sufficiently so that the opening of the at least one hook does not provide any longer an abutment surface to make the carriage (11; 44) and the load supporting structure (12; 43) translationally integral with each other when the carriage (11; 44) is placed in the second, so-called ground laying position. - the load supporting structure (12; 43) and the rear side of the carriage (11; 44) are connected by at least one rotary joint comprising, on one hand, a pivot pin carried by one of the carriage (11; 44) and the load supporting structure (12; 43), and, on the other hand, at least one hook carried by the other of the carriage (11; 44) and the load supporting structure (12; 43), the at least one hook having an opening in which said pivot pin is removably accommodated, the opening of the at least one hook thus providing an abutment surface allowing to make the carriage (11; 44) and the load supporting structure (12; 43) translationally integral with each other so that a translational motion of the carriage (11; 44) causes a translational motion of the load supporting structure (12; 43), and - means are provided, in the rear end region of the one or more guiding members (18; 45), for tilting the rear side of the carriage (11; 44) downwards with respect to the mean longitudinal axis of the or each guiding member (18; 44), so as to bring closer to the ground the one of the pivot pin and the at least one hook that is carried by the carriage (11; 44), sufficiently so that the opening of the at least one hook does not provide any longer an abutment surface to make the carriage (11; 44) and the load supporting structure (12; 43) translationally integral with each other when the carriage (11; 44) is placed in the second, so-called ground laying position.