Data from a trans-Atlantic study of 531 cars in the United States and United Kingdom has shown the Environmental Protection Agency (EPA) fuel economy figures only 1% higher real-world averages, compared to an 18% difference for UK cars against the EU’s New European Driving Cycle.

Emissions Analytics carries out real-world economy testing published as What Car? magazine’s True MPG figures in the UK and Motor Trend’s Real MPG in the United States. Both use the same equipment and methodology, which allows for variations such as the widespread use of air conditioning in California.

Testing included 101 cars from the United States, where the average economy was 33.3% and best and worst performers varied by 17% above or below the official figures respectively. In the UK, the 430 cars tested averaged 44.1%, with the best performer averaging 10% above official figures and the worst under-performing by 43%, according to the company’s data.

Emissions Analytics pointed out that the NEDC cycle includes urban and extra-urban driving over a total distance of 6.8 miles, while EPA test involves five cycles, covering city, highway and high-speed driving, plus tests in hot and cold weather, a total of 43.9 miles. Each year, the EPA tests 15% of vehicles, issuing fines for those which don’t come within 3% of manufacturer figures.

‘It would appear from the test data gathered to date in the USA that the EPA figures are well calibrated to average driving, although variations in the real world can lead to divergence from this by up to 20%,’ Emissions Analytics said.

‘We are now running at full speed in the USA and will be testing upwards of 250 passenger cars per year. It will be interesting to see if a gap between statutory and real world fuel economy starts to appear as the pressure to deliver the best fuel economy label grows.’