US / Euro mileage calcs
 

I'm just wondering how the US EPA mileage figures are calculated and how similar the methods are to the way the european ones are figured out. Because Current generation like the VW Jetta seems to get different figures if I convert the Euro MPG (IMP) to MPG (US) and then compare the US number to Our Euros

I've been working in the Auto industry on this side of the pond for years now and I can't see much we've got different in terms of tech. I used to work where they built the saturn's current astra - and they had no mech differences to the Opel astras yet they don't seem to get the mileage over there.... I'm very confused :(

It's a very controlled driving circuit that every car runs on. The Japanese, Euro, and USA circuits are different, so you get different results. In 2008 the US EPA changed the test, which lowered the ratings for all cars.

How Vehicles Are Tested
Detailed Test Information

I believe that the agerage for each car is derived from some x% city/(100-x)% highway formula. How they get the city and highway numbers s a different story. I've been wanting to look into that lately.

I remember that in the mid '90's auto makers in Poland (and maybe Europe) would give FE numbers for city, 90 km/h and 120 km/h. Then it got changed to city/highway/average, but I've never been able to find what exactly 'highway' means. Is it 90 km/h, 120 km/h, or maybe the average of the two?