March 2014 – Transatlantic testing

This month, in preparation for a presentation we are giving at the 24th CRC Real World Emissions Conference in San Diego, we have been making a detailed examination of the data we are collecting in America.

In most respects the emissions testing we perform in the USA is identical to the work we do in the UK. We use the same equipment, the same methodology (with some adjustments to account for factors such as the widespread use of air conditioning in California) and even our technicians travel between sites to ensure continuity in our processes.

In the UK, the data is published by What Car? magazine under the brand True MPG and in the USA it is published by Motor Trend magazine as Real MPG.

However, despite consistency in the testing process there are marked differences in the results. One of the most noticeable differences between the UK and the USA is that the statutory figures provided by the Environmental Protection Agency (EPA) are a closer match to real world figures than those generated using the New European Drive Cycle (NEDC). As can be seen in this graph, Real MPG is within 1% of the EPA combined figure compared with an average of 18% below statutory in the UK.

Mar pic

The test cycle in the USA was improved in 2008 and now involves five tests: the city, highway, high speed (up to 80mph), hot (with air con) and cold at 20°F (-7°C). The total distance of the five tests is 43.9 miles and takes 1 hour 35 minutes to complete, compared with 6.8 miles and 19 minutes 40 seconds in the UK. In the US, 15% of new models are tested by the EPA to check the manufacturer figures, and failure to come within 3% of the published result can lead to a hefty fine.

Some more comparisons between Emissions Analytics’s data from the UK and USA can be seen in the table below.



Number of cars tested



Average miles per gallon



Best performer against statutory figures



Worst performer against statutory 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%. 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.