Fuelly should consider adding the option to display fuel economy in gal/100 miles, eg. similar to the European standard of L/100 km, but in English (American?) units.
This has been suggested in other forum posts, and Fuelly seemed open to the idea, but not eager to do it right now. Here's why I think you should: since one goal of the web site seems to be to encourage people to think about and achieve better fuel economy, you should provide the best data for making rational decisions about fuel economy. Expressing fuel economy by miles per gallon does not lend itself to good decision making, basically because increasing mpg from 40 mpg to 50 mpg is not nearly as big an impact as increasing mpg from 20 mpg to 30 mpg. When considering fuel economy you want to know how much less gas you're going to use (or equivalently how much less $ you will spend). Unfortunately, this is not directly related to changes in mpg. For more, see this web site: http://www.mpgillusion.com/2009/02/overveiw-of-gpm.html
Here's a quote from there:
"MPG tricks people's perceptions. Replacing a car that gets 14 MPG with a car that gets 17 MPG saves as much gas for a given distance as replacing a car that gets 33 MPG with a car that gets 50 MPG (about 1 gallon per hundred miles)."
I know that Fuelly offers the option for individuals to add a gal/100 mile statistic to their page, but that's not the same as offering it as a display mode for the entire site. The later is much more useful for example, if someone is considering buying a new vehicle and wants to browse the cars on the Fuelly site to compare fuel economy of several cars.
We offer gallons/100 miles in the "mini-stats" section of vehicle pages. You can add that to your stats display and you'll see it on any vehicle page you visit.
I completely understand that you'd like us to be more proactive on this front and advocate for change in the way people compare fuel economy. But this is not an insignificant change. Adding a top-level fuel economy unit across the site takes a lot of time and resources and we already have a long to-do list.
I think people in the US would like to see this because we don't use Litres or Kilometers for anything. Everything is in gallons in miles. So people can wrap their heads around the idea of a gallon—and 100 miles.
If we were to implement this more widely it would be confusing for UK folks. But in theory, UK folks should be more used to km and L as measurements. So L/100km is a viable measurement for them, not so much for folks in US.
I know people want to see advocates for this measurement in the world. We're not ready to be an advocate for it beyond what we're already doing, sorry.
I don't think Imperial GPHM will be needed since Fuel in Canada and UK are sold in liters, and people on TDIclub regards imperial gallon-based fuel statistics as cheating. Only the US-GPHM will be needed as it is the most affected area of the MPG illusion.