Abstract: The devices for transmitting a traction force to the middle truck apply the force at a theoretical point of attack at a height (h) above the rails so as to have a moment exerted on the middle truck during traction which relieves the load on the leading axle of the middle truck by an amount equal to the relief force on each axle of the leading truck. Likewise, a load is added to the trailing axle of the middle truck equal to the force added to each axle of the trailing truck. This height is defined as ##EQU1## where a and b are the spacings between the axles and H is the height of the draw hook above the rails.