The relevant number for a semi isn't "miles per gallon" but "gallons per (cargo)ton-mile". (Which is not to say you couldn't make some improvements, but you're

The relevant number for a semi isn't "miles per gallon" but "gallons per (cargo)ton-mile". (Which is not to say you couldn't make some improvements, but you're never going to get 50 mpg while hauling 40 tons.)