Economy is better defigned as mass moved per gallon of fuel, an average semi gets ~8 mpg pulling 40,000 lbs
If the car is empty and you base the economy based on weight carried
40000/96=416 trips times 2 to move the same weight from A to B
so 2500/832=3 meaning a truck towing 40K lbs has to get 3MPG to be more effecient, this is unlikely because there needs to be someone driving it.
if I was sitting in the vehicle and it still got 30MPG
40000/296=135 trips times 2 to move the same weight from A to B
so 2500/832=9.259 meaning a truck towing 40K lbs has to get 9.3MPG to be more effecient. This shows that we are not breaking new ground here where a new truck will easily meet or beat this efficiency and it is essentially a wall moving through the air.
O and yea the Truck effeciency is based on 70MPH so this more than doubles the advantage in the trucks favor.