All my calculations are more pessimistic than published values. And no matter what I do I can't seems to come up with numbers that are both realistic and are as optimistic as published. But it is possible that tweaking a few input parameters would give a better approximation. Anyhow these new numbers show (you may have to refresh your browser) that aerodynamic drag is significant for all types of vehicles. For a commuter bus aerodynamic drag accounts for 82 percent of mechanical energy (after engine losses), while for a city bus aerodynamic drag is still around 43 percent of mechanical energy, even if the bus stops every 1/2-kilometer on a 100-km distance. A Superbus would reduce weight, and frontal area, and be suitable to reduce mpg for both types of bus. Overall, the heaviest, boxiest vehicles have the worst fuel consumption of all. The fuel consumption of a bus is predicted to be worse than a fully-loaded tractor trailer.