This site is great and I believe real mpg database can really be helpful for people. Still, I think real mpg values can be made more accurate by separating city and highway traffic mpg values. For example I own a 1.2 TSI SEAT Leon and consistently achieve 43mpg in mostly heavy city traffic. However, I also managed 61mpg a few times with 50-60mph steady cruising speeds in long journeys. There is a large gap and this gap can appear between two similar cars as well (For example, Volkswagen 1.2 Golf).

If people who drive mostly motorway driving submit mpg figures for one car and people who mostly drive during congested city traffic submit for another car, then the comparison may not be accurate. If the database can be adjusted such that it also displays the average submitted mpg values for city and highway traffic, it would be great and more consistent. Also as you know official mpg is based on NEDC, where it takes 4km city, 7km highway driving. Therefore average city mpg can be multiplied with a factor of 4 and highway with a factor of seven as their contribution to combined average mpg value.

This way real MPG figures can be very accurate, really helping people to choose a car.