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ICCT: gap between official and real-world fuel economy figures in Europe reaches ~38%; call to implement WLTP ASAP

Divergence of real-world CO2 emissions from manufacturers’ type-approval CO2 emissions for various on-road data sources, including an average estimate for private and company cars as well as all data sources. Source: ICCT. Click to enlarge.

The gap between official and real-world fuel-economy figures in Europe has risen to about 38%, according to a new report published by the International Council on Clean Transportation (ICCT). Ten years ago the discrepancy between these real-world and sales-brochure values was at 10%. The new report—“From Laboratory to Road: 2014 Update”—updates ICCT’s original 2013 report on the growing discrepancy. (Earlier post.)

The new report is based on data from more than half a million private and company vehicles across Europe. The findings come as the European Commission is preparing to adopt an improved test procedure that would produce more realistic vehicle test results.

The new report, jointly prepared by the ICCT, the Netherlands’ Organisation for Applied Scientific Research (TNO), and Germany’s Institut für Energie- und Umweltforschung Heidelberg (IFEU), unveils the increasing real-world efficiency gap using systematic statistical analysis.

A technically precise definition of real-world driving conditions is elusive because of the large variation in vehicle types and driving behavior. However, by aggregating large sets of on-road fuel consumption data, clear trends can be observed. This methodology is the basis for the analysis in this report. The data sources comprise eight different data sets covering as many as 13 model years, including both private and company cars, from various European countries. In total, these sources furnish fuel consumption and CO2 emission data from more than half a million vehicles.

—“From Laboratory to Road: 2014 Update”

The data show that for private cars, the difference between on-road and official CO2 values rose from around 8% in 2001 to 31% in 2013. For company cars, the gap is even greater: 45% in 2013.

The analysis draws on data from a number of different sources: the user websites (Germany) and (United Kingdom); the leasing companies Travelcard (Netherlands) and LeasePlan (Germany); the car and consumer magazines AUTO BILD (Germany), auto motor sport (Germany), WhatCar? (United Kingdom); and the car club TCS (Switzerland).

As one result of the growing spread, motorists are spending an average of €450 (US$570) per year more on fuel than if that non-performance gap were closed. The increasing gap also more than halves the official CO2 reductions achieved during the last ten years, making it more challenging to meet the EU’s climate change mitigation objectives. For governments, the growing gap causes significant losses of tax revenues. This is because vehicle taxes are based on laboratory test results instead of real-world data. For the Netherlands alone, the loss in tax revenues could exceed €3.4 billion (US$4.3 billion) per year, according to the ICCT estimate.

One new feature in the 2014 report is an examination of vehicle models. When looking at individual vehicle models, the ICCT researchers found that when a new vehicle model generation is introduced, the gap suddenly increases from one year to another Looking at 26 of the top-selling models in the EU, they found that for vehicle model changes before 2009, each time a new generation came on the market, the average gap increased from 12% to 17% of the official CO2 value from one year to the next.

For more recent model changes—after the EU CO2 regulation for new cars was introduced in 2009—they found that the typical increase in the gap from one generation to the next jumped even more, from 18% to 29%.

Average gap for the 26 top-selling vehicle models in the EU, immediately before and after introduction of a new model generation or major facelift. Source: ICCT. Click to enlarge.

The authors noted that “it is reasonable to assume that driving behavior has not changed appreciably over the past years.” Instead, they suggested that the observed increase of the gap is most likely due to a combination of:

  • Increasing application of fuel-saving technologies that show a higher benefit in type-approval tests than under real-world driving conditions (for example, stop- start technology).

  • Increasing exploitation of “flexibilities” (test tolerances and insufficiently defined aspects of the test procedure) in the type-approval procedure (for example, during coast-down testing).

  • External factors changing over time (for example, increased use of air conditioning).

Manufacturers measure vehicle fuel consumption in a controlled laboratory environment, using a test procedure called the New European Driving Cycle (NEDC). This procedure was developed in the 1980s and was not originally intended to be used for fuel consumption testing but air pollutants. A new and more appropriate test procedure, the Worldwide Harmonized Light Vehicles Test Procedure (WLTP), has been developed through the United Nations and is ready for implementation in the EU as early as 2017.

In the new test procedure, for example, the weight of the vehicles will be reflected more realistically—one of the aspects that will help to reduce the current fuel-economy gap.

It is important to clarify that this analysis is not intended to incriminate vehicle manufacturers. The NEDC was not originally designed to measure average fuel consumption or CO2 emissions, and some of its features can be exploited to obtain artificially low results. Manufacturers appear to be taking advantage of permitted flexibilities in the NEDC, resulting in lower CO2 emission values. The new Worldwide Harmonized Light Vehicles Test Procedure (WLTP), with its more dynamic test cycle and tightened test procedure, is expected to result in somewhat more realistic values. … A key aspect of the transition will be an appropriate conversion of existing CO2 targets and CO2 based taxation schemes from NEDC into WLTP. Unintended flexibilities that are currently part of the NEDC should not be accounted for when transitioning to WLTP. Otherwise there is a risk of undermining the introduction of WLTP and making most improvements achieved with the WLTP obsolete.

At the same time, the WLTP will not resolve all open issues, and the new procedure may itself have vulnerabilities that have not yet been identified. In light of this, it is important to complement the WLTP with additional measures, such as testing and regulating the efficiency of vehicle air conditioning systems. More importantly, some form of in-service conformity testing should be required to ensure that reasonable emission values are achieved not for a single test vehicle alone but for all cars sold to customers and driven on the road.

—“From Laboratory to Road: 2014 Update”


  • Peter Mock, Uwe Tietge, Vicente Franco, John German, Anup Bandivadekar, Norbert Ligterink, Udo Lambrecht, Jörg Kühlwein, and Iddo Riemersma (2014) “From laboratory to road: A 2014 update



Who know the major reasons for such a wide gap.
Would car manufacturers have something to do with it?

Meanwhile, let's multiply the stated fuel consumption in mpg by 0.60 to get close to real fuel consmption in mpg for EU cars and by about 0.80 for most USA cars.

The recent average USA new car fleet = 25.4 x 0.80 = 20.3 mpg.

The recent average EU new car fleet = 40.5 x 0.60 = 24.3 mpg


Top reasons for this:

Always hitting red lights - Need more micro hybrids, or full hybrids to recover energy.
How many years before everyone can use the EnLighten App to avoid burning fuel and brakes?

Winter warm up losses. Lots of new ways to improve are coming to market.

More weight in car in real world versus testing?

Low tire pressure? Make TPMS mandatory.

Front end alignment degradation.

Engine degradation.


Most people think they should get the advertised fuel efficiency (if they even calculate it) without regard to how they drive, and most people drive very inefficiently. The mileage label on a car should show a range of mpg, "depending on your driving style." I think most people would be shocked at the variation, and that might prompt them to learn what they could do to drive more efficiently (not that they would actually change their bad habits!).

I get significantly better mileage than the Mulroney label indicates for my car, without resorting to extreme hyper-miling techniques, so don't blame the test procedures.

Bob Wallace

"Top reasons for this:"

Top solution for this:

EVs ;o)

Solar and wind have become so cheap that inefficiencies caused by things like whooshing away from traffic lights cost little and cause no environmental damage.


Top reason for this?

EU is pushing manufacturers to lover CO2, they will use any means necessary to meet the targets.


Cutting total vehicle weight by 50% + more braking energy recovery would drastically reduce the NET energy required to take off at every stop.?


The most realistic figure to go by when considering the European Cycle is the "combined" figure, not the "extra urban figure" which is more aligned to the best you will ever get if you drove like Miss Daisy.

In my recently purchased car - a 2006 model with V6 2.7 litre Diesel engine, I can easily beat the 40.1 mpg combined claimed figure and even reach the claimed extra urban figure if I have a nice quiet flat empty road and take it nice and easy at a constant 55 mph.

It may have something to do with cars having smaller engines which are tuned to maximise power delivery. Unfortunately you will never get the stated mpg figure if you have to "drive it like you stole it" to get the power it promises especially on hilly roads.


The EU has really messed up here, letting this get so out of hand.
But it is a lot more than an academic question, it has a huge impact on motor taxation, both at sales level and annual road tax level, both of which are based on Co2 emissions in many EU countries.
The last 5 or so years have been a happy time for EU drivers because the newer cars have been more "economical" than the older models. Thus they have attracted lowed taxation rates.

Now suppose they reset the testing procedure and the My 2015 cars get 25% lower mpg and 25% higher co2 figures.
What happens to the taxation rates ?
Do you do nothing, in which case the price of new cars goes up quite a bit (manufacturers won't like that), also the annual road tax rates.
Or do you change your thresholds such that 125 gms on the new system = 100 gms on the old system ?
This would take a lot of organisation -and what do you do with older cars - do you apply the "old" thresholds to them, and a new set to cars after 2015?

Lots of conundra for governments and tax experts.

Also, I would like to see EVs and PHEVs set their CO2 levels based on the miles / KwH and gms Co2 (typical per country) / KwH.

You could split pollution taxation into two: local and global.
Local would be tailpipe emissions (EVs do very well here), Global would be CO2, pollutants from burning coal etc, (EVs do not do so well here [except in France and other low Co2 electric power countries]).


Here's an even more complex way of taxing EVs.

When you connect to a charger, it monitors how much CO2 is being generated per KwH at the time and sums up the amount of CO2 used to charge the vehicle.

You would be informed of this and billed annually as part of motor tax. (The same could be used for all electricity used.)

Why ?
The CO2 intensity of electicity varies during the day based on the sources of the power - if it is windy in Ireland or Denmark, the level will be low because of the windmills.
If it is sunny in Germany or Spain, the level will also be low due to the amount of solar.

Wind generation can be predicted quite well at least 1 day in advance, ditto for solar (!), so people could chose when to charge to avail of the lowest rates in terms of generation cost and CO2 taxation.

This is realistic for people who plug in at work and at home all night. In this way, you could nudge people to charge when the electricity is cheapest or lowest CO2.

[ Take a bit of work, mind you ]


I do not trust politicians one bit.

Changing what are really Figure of Merit measures of fuel economy to another scheme, is bureacratic makework. It indirectly amounts to a major tax increase WITHOUT having to vote for a Tax increase, so it is certain to happen.

Why is "pollution" only CO2?

Europe even with the new EU VI standards, still allows substantial genuine toxic pollutants, much more then in America. Which by the way is preparing to tighten to make an ICE powered car indistinguishable from an EV, in genuine toxic emissions. Europe is merely matching US standards of the 1980s, which have been tightened once more since then, with another tightening following soon.

North America already bio-sequesters every gram of anthropomorphic CO2 that it "creates" and the some more besides.

Europe, for one who travels there fairly commonly, literally reeks of diesel stink. It is no wonder your monuments are covered in scaffolding, as they try to remove the diesel soot from building surfaces. Imagine what it is doing to your citizen's lungs.

Clean up your act, rather then spending time changing meaningless Figure of Merit measures of fuel economy, as an excuse to raise taxes without having to vote for doing so.

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