In his book "Common Carriers" John McPhee says that the "common weight limit for five-axle eighteen-wheelers is eighty thousand pounds" [page 22] and the the rig of the driver he rode with while writing part of the book "gets a smidgen over six miles per gallon" [page 23].
That's 40 tons and 6 miles per gallon or 240 ton-miles per gallon.
Typical 2 ton autos get what 20 mpg? That's 40 ton-miles per gallon.
Certainly there is more to the mileage that a vehicle gets than its weight coefficient of drag, diesel vs gasoline, number of gears, acceleration come to mind.
What keeps our cars from getting so much less ton-mileage per gallon than our trucks?
Are there any practical things that auto and engine makers can learn from trucks to substantially improve auto mileage?
JKA