Something I was wondering about. I was doing some calculations on how much energy different types of vehicles consume, and I got a result that surprised me. For big trucks, I found an estimate of 5-6 MPG on the internet, divided the energy content of a gallon of diesel fuel by that, and then corrected for a ~45% efficiency. For the cars I divided the battery energy content of the Nissan Leaf by its range to get miles/joules. To check my results I tried doing an estimate for an electric truck with a battery as big in proportion to its (fully loaded) weight as the Nissan Leaf and I got more energy required for a given range than with the 5-6 MPG based calculation. I'm wondering if this is an artifact of my calculation (could easily be, it was just not very precise amateur work), or if there's some kind of genuine economy of scale for big vehicles that I stumbled on. I did a little searching on the internet and found that air resistance is a very significant factor in energy efficiency at high speeds (over half the power demand at 65 mph - http://www.rvtechlibrary.com/engine/MPG_Secrets.pdf" [Broken]) and its partially proportional to the vehicle's frontal area. A fully loaded big rig certainly is going to have more frontal area than a car, but I doubt it would have 25 times the frontal area (proportionate to how much heavier it is). If the car is 1.5 X 2 m (4.5 X 6 ft) and the truck is 3 X 3 m = (9 X 9 ft) the truck is going to have 3X the frontal area, nowhere even remotely close to 25X. Is there an actual economy of scale in energy with big long vehicles like trucks because of this? Does anybody have any idea how to actually calculate how big of a difference this factor would make to energy consumption of a large truck vs. a regular sized car? Thanks.