On rail, every load will be subject to harmonic or vertical vibration. Over-the-road trucks do not experience this vibration. What this means is the load will actually float at one speed. Five identical loads may each float at different speeds. If a train happens to operate for an extended period at the critical speed for a particular load, the product will begin to move laterally and longitudinally. If the units are not tightly wrapped or banded to a pallet, the stack may fall apart. This is often mistaken for impact damage which it is not since adjacent units are often intact. To stop or reduce this movement, we need to apply very basic blocking and bracing to maintain well unitized product in its original position. i.e. 18" 2x4 secured with 16d nails in a staggered pattern spaced 4-5" apart.