Average? I'm guessing about 700-800#.
I've hauled as little as a 3 ounce envelope of labels about 500 miles.
Or a 5 pound box of fasteners from Laredo to Smyrna, TN (1100 miles).
I was also "surprised" by an underestimated mold from El Paso to Portage, MI last summer. I should have refused...