6 u2032 turns with respect to car 6 in the part of the device closest to the wheel 7 located in the inner part of the curve the rod 14 turns with car 6 u2032 and shifts toward the left reducing its distance with respect to car 6 since the inner surface of the stop 3 has an inclination corresponding to that of the outer surface of the wedge shaped slide 2 when the rod 14 shifts toward the left it pushes the slide 2 which makes the stop 3 protrude toward the inside of the curve in the direction perpendicular to the respective lateral face of the protruding element 9 of the car 6 the slides 2 shift inside the corresponding support parts 1 which in the embodiment shown in the figures are u shaped the elastic means 13 protruding from the front edge of the car 6 in the part of the device closest to the wheel 7 and which is supported on the end face with a smaller surface area of the slide 2 is pushed and compressed by the slide 2 when it is traveling on the curve as observed in fig5 b when it returns to a straight stretch the rod 14 stops pushing the slide 2 whereby the elastic means 13 return to their rest position and the stop 3 is inserted returning to its original position.