This is a solution looking for a problem. This just solves the 'I save exactly x gallons' while most people just want to drive to work slightly cheaper.
The problem is that "miles per gallon" gives you a false impression of your costs and the fuel savings you get by switching to a more or less fuel-efficient car.
This is likely not a problem that many U.S. citizens are aware that they have, though.
I think it's pretty clear that the problem is car pollution. Like the article says, effectively communicating a cars "greeness" is the point. However, I do admit that changing completely to this number might be a bit weird. I'm not very good at math, but wouldn't the GPM number be a decimal usually? Like .025 GPM? That might be a bit of a mental leap for the general population to take.
I suppose a compromise could be reached if these numbers where used in tandem i.e. 15mpg/.0XXgpm
edit: Scratch that. It's not really about car pollution as it is about conservation of fuel/saving money which are different things.
In Germany you usually talk about how many liters it takes to drive 100 km. And you get numbers of around 5 to 10 (or higher).
Even the article says: "When the tests were repeated using gallons per 100 miles, the volunteers correctly picked the greenest option from those available."
Yeah, as the Verizon reps made stunningly obvious[1], the average person struggles with small decimals, but making it a figure like gallons per hundred miles (or liters per 100 km like I have seen in Europe) would make it easier.
I heard a similar story to this on NPR the other day. It pointed out that the EPA already gives it's efficiency ratings in gallons per mile, which are then converted back to miles per gallon for the (not so) benefit of the consumer.
I actually really liked the idea of gallons per 10k miles. This gives a nice beefy number to think about. For instance, my 2004 Chevy Aveo uses 294 gallons per 10k miles. My dad's truck uses 625.
I think they could take it even further and just put a dollar figure on the car. Say the entire industry agrees that 15k miles a year is normal. Pick a gas price for that year and put the total cost of gas on the vehicle. At $3.50 a gallon, my car would have $1544 on the window, whereas my dad's truck would have $3281. That is a difference that is immediately obvious to everyone. They do something similar with appliances, where they list the estimated annual operating cost, which makes picking the most efficient fridge quite easy.
