It might be not so hard to take some weight off of newer trucks. It's even possible to make a tougher frame using less raw materials, such as a truss-frame instead of a ladder-frame or a backbone-frame similar to the one used in Czech-made Tatra trucks. Alternative materials such as fiberglass can be more widespread in body panels to cut weight, and vegetable fibers can be used instead of fiberglass - eventually giving an economically-viable usage to agricultural residues such as wheat straw (reported to be already used by GM to reinforce interior trim plastic parts).