Eco-nomics: Fuel Efficiency - There Should be an App

Okay app nerds, here is an idea for a good one (though probably not a profitable one).  Today's fuel efficient cars are fuel efficient in very different ways.  Diesel cars tend to be very efficient at constant revs but less so the revs vary a lot, thus they are great for highway driving, less so for city driving.  Hybrids are the opposite, the electric motor does a lot of the heavy lifting in the city but the gas engine has to kick in on the highway.

So what car is right for your particular driving habits?  A lot of us can make some generalizations about our driving and many might be able to point the car to purchase if our goal is to burn a little fuel as possible.  But there a probably lots of folks like me whose driving habits don't provide a clear cut answer.  For those people I think the new smart phones can provide a precise answer.

The app would be simple, keep track of city versus highway driving by using the GPS function of the phone.  Feed the data into a simple algorithm that computes combined fuel efficiency for your particular driving habits for every car for which the EPA provides fuel efficiency estimates.

Shazam!  Here are your top 5 fuel efficiency choices.

Brilliant! I think I am the second coming of Steve Jobs, perhaps Apple will call...

Things I Think About When I Should be Thinking About Other Things

Why don't medical practices of a decent size have on-site pharmacies that dispense the simple stuff?  It seems to me that most of what a family practice prescribes is anti-biotics, why don't they just dispense that stuff themselves?  More exotic and problematic drugs (like narcotics) can be left to the big pharmacies, but it would seem a fairly simple thing to dispense the other stuff.

But as an economist, I figure there must be a reason since it doesn't happen - either with the economics or with the regulation - so what is it?  Anyone know?