Speaking with industry paper Automotive News, the Agency's Christopher Grundler said the gap between EPA figures and those of the carmakers had grown “unacceptably high” in the past few years.
In 2007, the gap was 1.15 percent but by 2010, the gap had doubled to 2.25 percent. In one case, the gap was 14 percent, which would have seen a claimed figure of 10.0 l/100km become 11.4 l/100km.
Mr Grundler said that some of the drivers used by carmakers during testing were simply ‘too good’, setting impossibly low figures that could rarely be achieved during normal driving situations.
"The industry has some very good drivers, and we've noticed," Mr Grundler said.
“It is not cheating, it is just taking full advantage of the rules.”
It is believed that the best drivers can ‘level out’ hills and valleys, using careful throttle and brake applications, and the EPA is now demanding a copy of the vehicle’s telemetry used to evaluate fuel figures.
The Agency is also looking to refine the testing procedure to reduce the gap. But a call to replace human drivers with robots in laboratory testing has been met with opposition, with claims a robot driver would make it even easier for carmakers to set unrealistically low fuel figures.
Without the element of human error, it is believed carmakers armed with the knowledge of how the robot will behave during a test could simply configure engine management systems to run as economically as possible; vastly different from the set-up offered for sale to the public.
A robot-driven test could also prove to be even further removed from the ‘real world’.
Australia uses similar methods to gauge fuel consumption and also accepts European Union figures to be correct without re-testing.
There are plenty of examples of scepticism locally too, with Queensland’s RACQ saying that test figures “cannot be used as an indication of the fuel consumption a vehicle might achieve under actual operating conditions”.
Some carmakers have taken steps to 'back up' their official figures, however: Volkswagen's annual ‘Think Blue’ challenge aims to prove that ‘official’ fuel consumption figures are not only achievable in the real world, they can be beaten.