If you read the full report, the automaker with by far the largest gap between its claimed improvements in fuel economy and its actual on-the-road performance is General Motors. Much worse than VW and Mercedes (who also did very poorly), by this measure. A reckoning is coming. source: see page 13, here http://www.transportenvironment.org/sites/te/files/publicati...
"3. Deducting 4% from measured results Bizarrely the NEDC procedure allows carmakers to actually declare (use) a value 4% lower than the one measured. The provision is designed to minimize the testing burden but is being abused by carmakers to declare lower test results systematically." I wonder if there is a person that didn't expect this to happen.
This is going to sound backwards, but consider this: People buy cars based in part on MpG, however MpG is within itself an abstract thing (i.e. you don't actually get X miles per gallon, never did, never will too many other factors to include).
So if everyone removes 4% from an abstract number, the entire market has shifted down, but the relative difference between two models remains identical (e.g. if one car has 21 MpG and another has 25 MpG, even with 4% removed from both they retain their relative position).
If some were removing 4% while others weren't, that would legitimately be a problem. If they're all removing 4% then we're essentially where we would be at the start just with lower abstract numbers.