UK-based Emissions Analytics has confirmed the gap between the current legal emissions testing regime and real-world testing with Euro 6 diesel NOx levels four times the advertised amount and CO2 31% higher.

The company has tested more than 1,000 cars on the road in Europe and the U.S. in real-world driving situations to gather data on both fuel economy and emissions. Of the Euro 6 diesels Emissions Analyitics tested, it recorded on average an increase four times above the statutory limit of 0.08g/km. However,  this is an improvement, as this time last year they were seven times above, so "technology is moving in the right direction". Emissions Analytics would not "name and shame individual manufacturers, it's all about the data".

Nick Molden, Emissions Analytics chief executive, said: "For car buyers, this means that fuel economy on average is one quarter worse than advertised.

"This matters, even if no illegal activity is found. These differences may well be explained by limitations in the official system, rather than through illegality."

Emissions Analytics started testing tailpipe emissions on the road in 2011.

He said: "Based on our findings, we've felt strongly that this is the only way to truly understand real-world performance."

Molden shared results from his company's research during a presentation at the Automotive Testing Expo (Oct. 20-22) at the Suburban Collection Showplace in Detroit.

Molden pointed out that a more uniform way of testing new-model emissions and fuel-economy performance will soon be implemented in Europe with a recently-approved Real Driving Emissions (RDE) procedure that will more closely align lab testing with real-world results.

Molden said that RDE tests can be especially helpful in designing effective test cycles that eliminate discrepancies between lab testing and results from on-road testing.