That is correct, diesel burns almost all of the available energy that comes out of diesel fuel. Whats more, diesel requires higher compression ratio, that is why it does not have much horses in there. They have higher torque than gasoline, and that is what you'd want when it comes to haul heavy stuff.
City bus, average is 3 miles to a gallon. That DOES makes sense because of the weight involve and ultra frequent stops that bus require to make.
