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ICCT analysis shows growing divergence between official and real-world fuel economy values for new cars in Europe

Researchers at the International Council on Clean Transportation (ICCT) have used data from—a free web service that allows users to track their fuel consumption by entering odometer readings and the amount of fuel added during fill-ups—to calculate the divergence between official fuel consumption values in Europe and real-world performance.

Presented in a working paper, the ICCT findings show that after EU-wide CO2 standards were introduced in 2009, official fuel consumption values decreased by 15% while real-world figures only decreased by 2%.

Average official and real-world fuel consumption values of new European passenger cars. Source: The ICCT. Click to enlarge.

Real-world driving is a generic term that covers the wide range of driving conditions that vehicles are subject to during actual use. The real-world, on-road fuel consumption of cars varies depending on vehicle and road characteristics, driving style, and environmental conditions. Nonetheless, when looking at real-world fuel consumption data from a large numbers of vehicles, the results of the vast majority of vehicles tend to cluster around a central estimate, and official fuel consumption values have become increasingly unrepresentative of this estimate over time. More importantly, average real-world driving characteristics do not change significantly from year to year and, thus, should have little impact on the trends from one year to the next.

—Tietge et al.

Although almost all the new models in the Euro market exhibit that divergence, the ICCT found, the divergence can vary significantly between different models. Of the 20 selected top models examined:

  • Five models—the BMW 5-series, Mercedes-Benz A-Class, Opel Astra, Opel Corsa, and Toyota Yaris—actually increased real-world fuel consumption since EU-wide CO2 standards were introduced in 2009.

  • The Audi A4, BMW 3-series, and VW Passat made little progress, with less than one percent real-world fuel consumption reductions in the same time period.

  • The Peugeot 206-208 had the highest reduction in real-world fuel consumption values since 2009 (about 19%). The Ford Focus, Mercedes-Benz C-Class, Skoda Fabia, and Skoda Octavia all reduced real-world fuel consumption by more than 10% since 2009.

Reduction in official and real-world fuel consumption since 2009 for 20 popular car models. Data points are colored by vehicle segment. The two lines mark the 1:1 and 1:2 ratios between real-world and official fuel consumption reductions. Source: the ICCT. Click to enlarge.

A joint study by Element Energy and the ICCT identified four main factors behind the discrepancies, all primarily related to different flexibilities in the vehicle testing procedure:

  • Road load determination. Road load, or the aerodynamic and rolling resistances that a vehicle has to overcome during driving, have to be determined prior to laboratory testing. The ICCT said that manufacturers are increasingly exploiting flexibilities and tolerances in this stage—such as removing side mirrors, reducing vehicle weight, and using tolerances in the measurement procedure.

  • Laboratory test design. Vehicles are tested under conditions that are unrepresentative of average real-world conditions (e.g., ambient test temperatures of 20 to 30°C) and regulations allow for flexibilities and tolerances that manufacturers are increasingly exploiting, according to the ICCT.

  • Lower effectiveness of new technologies. Some fuel-saving technologies, such as stop-start systems and hybrid powertrains, tend to be more effective during laboratory testing than during real-world driving.

  • Other parameters. Auxiliary systems, such as air-conditioning and on-board entertainment systems, are switched off during vehicle testing but consume energy during real-world operation.

Additionally, the white paper noted, while the exploitation of these flexibilities in the current testing procedure explains the growing gap, the regulatory and institutional context does little to prevent it.

The ICCT authors make a number of recommendations to address the situation:

  • Establishing an EU-wide type-approval authority to act as a neutral party between vehicle manufacturers and technical service companies and and to be able to mandate vehicle recalls and impose financial penalties for non-compliance.

  • In-use conformity testing of randomly selected vehicles.

  • On-road fuel consumption testing. For NOx emissions, the European Commission adopted the Real-Driving Emissions (RDE) procedure, making use of portable emission measurement systems (PEMS) to verify that light-duty vehicles have reasonably low emissions of NOx during conditions that resemble real-world use more closely than laboratory cycles. This system of on-road testing could be extended to cover vehicle CO2 emissions—i.e., fuel consumption.

More generally, the current lack of transparency in the type-approval process and real-world performance of cars impedes independent verification of fuel consumption values.

—Tietge et al.




ICEVs manufacturers cannot be trusted with fuel consumption and GHG emissions. Real life consumption is 20% to 30% higher than they claim.

USA's fleet average is probably closer to 20 mpg than the claimed 24 mpg.

The same applies to electrified vehicles. Their year round all weather energy consumption is probably (at least) 25% higher than claimed and e-range 25% less?

Nick Lyons

So what's the deal with the Peugeot small cars, which seem to be the only ones actually complying with the standards?


Wait and see. They are being investigated?

Nick Lyons

This study was carried out by the ICCT, a third party, using user-reported data. I don't think Peugeot is diddling the data.


A huge amount of this is driving style.  I am not driving my own car at the moment, and I reset the trip computer in the substitute to start over.  The average fuel economy when I got it was 24.0 MPG; right now it is over 31 MPG.


Engineer poet is right, i know that if you drive on the slow side than your mpg increase. Im driving like if gas price were at 100$ a gallon, that it kill me when breathing it and other cars and truck and im earning 5 000$ a year. These are my perceiving costs, LOL. And i drive a small dodge neon 5 speeds that everybody lauph at at Also im pass by a lot of big suvs doing 85 mph. We learn more by assesing what is going on on the road then by reading greencarcongress pr autobloggreen.


In 2008/2009, in the UK at least, the motorway traffic slowed down very noticeably to save fuel (many doing just 60 mph) in response to the economic crisis. Now they've speeded up to where they were before. Perhaps this explains part of the gap? Also, as car performance has improved recently, perhaps we're driving faster for this reason too? Would be very handy to look at average speed in relation to this data.


It would be so easy to impose the 60 mph speed limit with a few more automated radars. The added revenues could be used to install more radars.

A single radar, in the proper place, created $18,000,000 in new revenues in 2015. That was too good for our politicians (and speeders) and it has been removed. It is very difficult to read those people.


It surely does depend on the driver, methodology etc thats why the article makes this valid point.

Easy to miss when spid reddin.

"More importantly, average real-world driving characteristics do not change significantly from year to year and, thus, should have little impact on the trends from one year to the next".

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