This focuses on improving efficiency in one vehicle over another. As you can see, I’ve added my Fuelly profile thing to the sidebar. I get about 33-37 mpg on average, depending on how frequently I have to drive side streets, which isn’t often. If I were to upgrade my car for a more efficient one, I would have to hit 50+ mpg to make the same improvement in gallons saved by driving the same distance as someone upgrading from a 16 mpg car to a 20 mpg car. It’s a real interesting way to look at it.