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ICCT study finds increasing discrepancy between type-approval and real-world fuel consumption in European cars

Differences in CO2 emissions according to type-approval values (set at 100%) and other data sources (compared against type-approval values) over time. ADAC EcoTest (NEDC hot) includes the effect of the air conditioning system turned on; ADAC EcoTest (NEDC cold) does not. Source: ICCT. Click to enlarge.

A new study by the International Council on Clean Transport (ICCT) has found that the gap between type-approval and “real-world” fuel consumption / CO2 values for European cars increased from about 8% in 2001 to 21% today, with a particularly strong increase since 2007. The study was based on the analysis of more than 28,000 user entries of the German fuel consumption database spritmonitor.de and more than 1,200 vehicle models tested by Europe’s largest automobile club ADAC.

The authors—Peter Mock, John German, Anup Bandivadekar and Iddo Riemersma—suggest that potential reasons for this increasing divergence include: (i) increasing use of existing tolerances and loopholes in the determination of road load, vehicle weight, laboratory test temperatures, and transmission shifting schedules for type-approval; (ii) inability of the current test cycle, the NEDC, to represent real-world driving conditions; and (iii) increasing market share of vehicles equipped with air conditioning systems.

From a consumer perspective, most drivers are aware that there exists a gap between the fuel consumption they experience during everyday driving and the corresponding values that are listed in information brochures they obtain from their local car dealer, the internet, or other media sources. As this gap increases, a part of the CO2 and fuel consumption reductions achieved on paper do not pay back to consumers in fuel cost savings. This could lead to a situation where official type approval values provided by the vehicle manufacturers would lose credibility among consumers and where the willingness to invest into new vehicle technologies to reduce fuel consumption and CO2 emissions is reduced.

—Mock et al.

To reduce its greenhouse has (GHG) emissions by 80-95% below 1990 levels by 2050, the EU requires a reduction of at least 60% by 2050 with respect to 1990 (70% with respect to 2008) from the transport sector—the only sector in which GHG emissions have increased since 2005 (+30% compared to -7% for all sectors).

The automotive industry agreed to a voluntary self-commitment for passenger cars to reduce the level of emissions for new vehicles in 1998/99. However, the annual rate of reduction between 1998 and 2006, as measured by the New European Driving Cycle (NEDC), was only between 0.6% and 2.2% and the target of 140 grams of CO2 per kilometer (g/km) for 2008 was missed. In early 2009 the first mandatory CO2 performance standards for passenger cars in the EU were adopted, setting a target of 130 g/km for 2015 and 95 g/km for 2020. In the course of setting mandatory standards, the annual rate of reduction of the average level of CO2 emissions from new passenger cars has increased from a rate of 1.7% in 2007 to 5.1% in 2011. The European average CO2 emission level in 2011 was 140.3 g/km compared to 158.7 g/km in 2007.

The ICCT paper focuses on new passenger cars in Germany—the largest market in Europe (3 million new passenger cars each year) and a major exporter to other countries (5.5 million passenger cars exported in 2010). Only CO2 values are reported; the conversion factors used are 2.43 kilogram (kg) CO2 per liter of gasoline and 2.65 kg per liter of diesel fuel.

In addition to identifying the growing discrepancy between type-approval and real world fuel consumption, the ICCT analysis confirms that there was a decrease in the level of CO2 emissions of new passenger cars in Germany since 2001. However, the magnitude of reduction in reality appears to be only about half of what is suggested by the type-approval values (about 7% instead of 15% since 2001).

These developments lead to two key concerns: a) From a policy maker perspective, to ensure that regulatory CO2 emission reductions result in similar ambient air emission reductions in order to achieve future greenhouse gas emission targets, b) From a consumers’ perspective, to avoid disappointment due to higher than expected fuel consumption, which could have negative implications for the willingness of consumers to invest into fuel efficient (and low-CO2 emission) cars in the future.

—Mock et al.

The authors explain the existence of a gap between type-approval and real-world levels as due to:

  • Characteristics of the NEDC test cycle are not representative for real-life driving behavior (low accelerations, low maximum speed, high idling time, constant speeds instead of transients, favorable shifting points, etc.)

  • Cold start testing is performed at ambient temperatures close to 30 °C, while real life temperatures are lower, leading to higher fuel consumption.

  • The allowed tolerances and flexibilities in the road load test procedure cause the road load of type-approval vehicles to be lower than that of production vehicles.

  • At the type approval test the battery is charged to 100% capacity.

  • The type approval test weight is lower than the real-life average.

  • Vehicles are type-approved without the air conditioning system turned on (or any other power consuming equipment).

  • Other flexibilities and tolerances in the type approval test procedure are exploited to positively influence the test results (e.g. tolerance allowed to follow the NEDC speed trace, allowed 4% tolerance between measured and declared CO2 value, etc.)

The authors also make a number of recommendations to address the problem:

  • Monitor real-world emission reductions on a regular basis—preferably by independent research—in order to reveal and address gaps between type-approval and real-world emission levels in a timely and effective way.

  • Ensure that the coming World Harmonized Light-duty vehicle Test Procedure (WLTP)—expected to apply to the EU type-approval from after 2015—is as representative for EU real-world driving as possible.

  • Improve test procedures as well as test cycles.




The way Germans drive on the autobahn explains a lot. Of course we need a new driving cycle and this work is already going on but an alternative approach would be to teach ecodriving to German drivers.


I think that for marketing reasons car manufacturers and goverments are falsifying the real numbers and in reality new cars don't make more mpg. Car journalists don't explain this because their jobs depend more from the new gadjets fad from the car manufacturers then truth from consumers.


Improved driving procedures could certainly help to lower fuel consumption.

However, in our general area (and probably in most populated areas), city and highway traffic jams are now very common 12+ hours a day, specially from early April to late November due to everlasting road and overpass repair works and during winter time due to snow removal and accidents. The growing number of school buses between 7h to 9h and 14:30h and 17:30 h can also slow the traffic flow and increase fuel consumption.

More suburb e-trains and subways to take more cars off the roads/streets, more car sharing, combined school and general public buses, street, road and bridge repairs between 19h and 06h only and improved driving techniques etc could give improved results.


Type approval in the EU is handled by an independent "technical service" (e.g. laboratory) that must be accredited for the work they carry out by another third party. As you can see in the figure, the same ADAC test as in the type approval (NEDC cold) is within 1-2% of the manufacturer’s type approval value. This is within normal tolerances of the test procedure. Thus, the results actually shows that there is no falsification of the data, in contrast to your statement. It verifies that if you pick a car from the street in relatively unknown condition, it will be very close to the type approval data. Why must the theory of conspiracy come up all the time? If we think that the 1-2% mentioned are “real”, the tolerances and flexibilities might explain this difference, as the authors of the study suggest. Maybe authorities could “tighten” this somewhat but the problem is certainly not the 1-2% difference. The main problem instead is that the NEDC cycle is not representative for normal driving pattern but also that the driving pattern (in Germany in particular but maybe many other EU countries, as well) should be changed via driver training. One good example is the following: In spite of the cold temperature in Sweden, I find that my own fuel consumption is very close to the type approval data and mostly slightly below. I practice ecodriving.


I think they optimize the vehicles to do well on these EU tests. I recall having read that one manufacturer went sofar as to specifically program a routine in its motor management to detect when the car was subject to the test and adapt its parameters to lower fuel consumption.

Another issue that I guess they overlooked is that of aerodynamics. Cars are optimised with computer models and in a wind tunnel to get a low drag coefficient. In computer models and wind tunnels there is a perfect airflow. But not so in real life where there are crosswinds and turbulence from other vehicles. Those disturb the perfect laminar flow that the designers aimed for. The less optimised cars of the past didn't have much laminar flow to begin with, so take less penalty.

Finally, the Prius. Fuel consumption takes a real hit for cold starts. The colder it is, the worse. The reason is the heater. As soon as you switch on the heater, it will let the engine run continuously to warm up and make it comfy for the driver. Only after warming up sufficiently, the full hybrid mode kicks in. Cold start fuel consumption really improves if you keep the heater off for the first few km. Nobody does this of course (except me :) But the 'cold' start at 30 degrees that is apparently the case for the EU test will never provoke this behaviour.

Another thing with hybrids in general is the matter of the traction battery. Do they measure charge levels before and after the test? If it ends the test with a lower battery level than it began, that would be another explanation for the discrepancy.


@ Peter_xx.
I practice ecodriving too till years and years to save gas but the price of gas had increased way more then the gas i saved so why is this ? Cars are supposed to be better but contrary to tv's and other product the price have been jack-up and they do less mpg with the added weight that they added over the years. I drive since 1977 so i know what im talking about. It's a market controlled by crooked oil compagnies, car manufacturers and wall street speculators and goverments. We always pay more for less.


My present car has ~30% lower fuel consumption than my previous model. Every car I have had since MY´83 (I did not really do any statistics before that…) has had slightly or significantly better fuel economy than the previous model. I will look for >10% improvement for my next car. By buying fuel-efficient cars rather than big monsters, we can create a market for the efficient ones. It should be possible for you to find such a car as well.


Cars are becoming so finely equipped and tuned for economy that they are less forgiving to less economical driving styles. Hence, only the most masterful of hypermilers who know the car, its technologies and how to optimise them all at once will know how to get the high mileages (and hence lowest CO2 emissions) in a way that is employed to achieve the official test figures.

For the more everyday who thinks driving regardless of style will achieve the claimed figures, they will be sorely dissapointed. Downsizing engines to a point where they are underpowered doesn't help. It encourages people to drive harder to achieve rasonable performance on the road - brisk acceleration (to overtake for example), uphill climbs etc all require significant efforts in an underpowered car which has a negative effect on fuel consumption. Cars with a more optimised engine size will have better torque levels which reduces to need to 'floor' it in anticipation of a hill or to get past a Sunday driver.

In the past older cars were more forgiving. In fact it's obvious that many weren't tuned to get optimum mileage/CO2 figures than they do now. Hence, I routinely get more then the combined figures for both the 1997 A6 2.5TDi and 1999 1.8T Passat and can even better the extra urban figures on long smooth runs. In the Audi over 60mpg is possible, even at 70mph and 45 mpg is possible in the Passat at 55-60mph.

Given the shortcomings, particularly with so called 'eco' models, my next car will be one that has a engine that is optimally sized for the weight of the car so that it avoid the issues related to underpowered engines.

To this end, it would be useful for a study to compare bhp and torque per ton with mpg per ton to give us a better idea where that sweet spot is in finding an optimum engine size. Engines that are too big and too small affect real world efficiency. Getting it optimally right is key.


I do not have any problems to get better fuel consumption on my diesel car. Practically the only thing you need to know is to shift gears at much lower engine speed than with a gasoline engine. This is, of course, more difficult with an automatic transmission.

My final point is that if you constantly drive at 200+ km/h on the autobahn, you should not complain about high fuel consumption.


I think you missed my point entirely.

Lets deal with your personal issue first. I cruise at relaxed speeds: 65-70mph on motorways and dual carriageways (divided highways if you're on the other side of the pond), 55-60 mph. Contrary to your mis-reading and accusation I have no problem getting mileage that exceeds the official figure (my own are in my post above!). Also, nowhere did I say I travel at 200km/h (125 mph). It was you alleging it. Aside, it's not legal in the UK. So be very careful not to distort other peoples points to score points of your own!

My second point goes back to the topic in question and the fact that automakers, under the tightening EU restrictions on CO2 emissions, are deliberately tuning their vehicles to perform optimally in the test rather than on the road. This is more the case with 'eco' models with downsized engines. In reality they tend to be underpowered. Think of trying to maintain a reasonable speed of 60mph on a motorway incline in the highest gear and you'll realise that having to change down gear is a sign that the engine is not ideally sized for the car.

I also know of people who have bought (or chose in the case of company car drivers) 'eco' badged cars and regretted it. Most claim that, even by driving carefully, their fuel consumption falls well short of the official figures. Others in versions without the 'eco' tweaks find that the mileage figures claimed are more realistic and achievable.


I did not say that I agreed or disagreed with you. I did not even comment on your statements. I just told you about my own experience and made a comment about driving on German highways.

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