In fact, the gap between ratings and real-world result has widened substantially during the past decade or so, as accessories such as stop-start engine technology and air-conditioning use are not properly factored in. The gap is distressing since automakers are charged with cutting emissions by more than 25 percent by 2021 to meet stricter European Union standards.
Of course, it's not like the European Union didn't know automakers' emissions ratings were a little too optimistic. Earlier this year, the EU said it was looking at a new testing program that more accurately measured real-world emissions levels than the traditional New European Drive Cycle (NEDC). At the time, the EU started pushing for what was called the World Light Vehicle Test Procedure (WLTP) and estimated that the NEDC may be underestimating emissions levels by as much as 30 percent. Where the extra eight percent came from, we'll ever know. But for those looking to dig deeper, the ICCT report can be found here.