If you're transporting wood, you want to make sure it's securely tied down so it doesn't shift during transport. One way to do this is to tie the pieces of wood together. This will keep them from moving around and banging into each other, which could damage the wood or cause it to break.
Another method is to strap the wood down with ratchet straps or rope. This will keep it firmly in place and prevent it from shifting during transport. Whichever method you choose, make sure the wood is secure before you start driving!