It would be interesting to have the option to specify how many passengers are in the vehicle and then show the fuel consumption per person.
An SUV that is full of people is more efficient than a toyota prius hybrid that has only the driver.
Thus people will start focusing on not-driving-alone rather than trying to save a few ounces of fuel with crazy driving techniques.
One hand, it would be nice as there's something in the mpg-per-person thing.
On the other, how would you enter this value for a tank?
I mean "I went to work 9 times alone, in two of the ways I took a detour to do some shopping and in 8 cases I shared the car with a colleague for 5.2 miles of the 11.4, but may be it was my other, 12.5-mile route? I don't remember. Went to the in-laws with the wife 5 times, returning their trailer once. They live 27.4 miles from us. Visited the zoo with the family, it was a 5-up drive, but my eldest daughter had other things to do so she came home by bus."
The question is: how many people were in the car?
And what if you have a fat and a skinny colleague whom you share the car with? Implementing mpgpp tracking is easy. Using it, on the other hand...