Cars.com calculates the real CAFE numbers with True Mileage Index!

TMI. What does that mean? Well, it usually means 'Too Much Information,' but in the case of fuel mileage, there is truly no such thing. Everybody and their brother wants to know what kind of mileage they are likely to get out of their next new car purchase, so we'll take any information we can get. With that in mind, Cars.com has gone to the trouble of calculating the mileage statistics of all the major brands sold in the United States and has sorted them by average miles per gallon. While the list doesn't actually break down each manufacturer further by model, it is still helpful in some way.
As you may be aware, CAFE mileage statistics aren't actually representative of what a given manufacturer is likely to achieve, as they are adjusted for all sorts of reasons. Therefore, Cars.com chose to go by the EPA's mileage ratings to calculate its figures. For the same reason, the impending fuel mileage requirements being proposed by the Feds aren't quite as harsh as they might seem. For instance, CAFE's 2007 rating for Honda's domestic passenger-car fleet comes in at 33.5 mpg, while Cars.com estimates a much more realistic 24.9 mpg. So, the EPA's estimations are still useful for comparing individual car models, and Cars.com's TMI rating is useful for comparing the manufacturers themselves. Remember, though... your mileage may vary.

[Source: Cars.com]