How Fuel Consumption Is Tested

Fuel economy is the single most talked about spec figures for hybrid cars. Japanese manufacturers will usually quote their figures based on the "Japan 10-15 Driving Mode" method while models sold in European markets will usually be quoted a figure from the "EU Combined Cycle". What do these numbers mean and how are they obtained?

Official fuel economy figures are never obtained by driving the cars on real public roads. But rather, the test cars are usually put on a dynamometer to simulate certain driving conditions. The test cars are strapped to the dynamometer simulating a "rolling road" drive, driven by a test driver according to a specific route and speed guided by a computer monitor. It is not possible to test every single model in the market so the government authorities will just have to take the figures provided by manufacturers, tested under approved methodologies in good faith. The authorities however will randomly test between 15 to 20 percent of all new models in the market every year.


These dynamometers used have a far more complicated setup than what you normally see in tuner shops, tracking not just power output but fuel and exhaust emission plus keeping track with a lot of other vehicle performance parameters. 

The EU Combined Cycle method was first drafted by the European Economic Commission and passed by the EU parliament in Brussels as the EU Directive 80/1268/EEC. Several revisions have been made and it is known as the New European Driving Cycle (NEDC). It came into effect in 1-January 2001. Manufacturers selling cars in Europe are bounded to reveal their fuel consumption figures based on the EU combined cycle and not the result of any internal test done according to a non-standard methodology, which will of course be rigged to the manufacturer's advantage.

Below is a speed-time graph showing what is termed as the driving schedule for the test.

The EU Combined Cycle method involves two test cycles :
a) Urban cycle which involves a series of acceleration, deceleration and idling. Maximum speed is 50km/h with a an average of 19km/h over a distance of 4km.
b) Extra urban cycle
Mimics highway driving at a maximum speed of 120km/h, with an average speed of 63km/h over a distance of 7km.

Both tests are done with the air-conditioning switched on. Ambient test room temperature must be at 22 degrees Celsius (plus-minuc 2 degrees) and the air-con is set at 20 degrees Celsius with the fan speed at 1/3 or 1/4. Cars with automatic climate control features will have the temperature set at 20 degrees Celsius and fan speed set to AUTO.

Results from the two cycles were combined and averaged.


Singaporean fuel economy label on a Toyota Corolla Altis 1.6. Compulsory on all new cars in Singapore since April 2009. Tested based on UN ECE R 101. However, Directive 80/1268/EEC currently used in Europe is also accepted. Owners of course have the right to remove them once they take delivery of their cars. It is more of a guide for consumers when shopping.


The Japan 10-15 Driving Mode, on the other hand was was drafted by the Japan Ministry of Land, Infrastructure and Transport. Like the EU test, there are two cycles.
a) The 10 mode mimics urban driving. The maximum speed is 40km/h, while the average speed is 17.7 km/h over a period of 135 seconds.
b) The 15 mode mimics highway driving. The maximum speed is 70km/h with an average of 33.88km/h over a period of 231 seconds.

Results from the two cycles were combined and averaged.

Immediately we can see why fuel consumption figures based on the Japan 10-15 mode will be grossly over inflated as the speeds were just far too low for real world driving. Take the Honda Civic Hybrid for example, fuel consumption figures based on Japan 10-15 driving mode is 31km per litre while the EU combined cycle gives 21.7 km per litre or 4.6 litres per 100 km. That's a whooping 43% difference! Purely due to the different methodologies used.

In their defence of the Japanese method, the test is merely a reflection of the driving conditions in Japan, where average speeds are much lower, with low speed limits and traffic laws are very strictly enforced. The speed limit on Japanese highways is 100km/h. The Japanese government recognises the problem with the current 10-15, especially for larger engine capacity cars sold overseas. A new JC08 cycle will come into effect by 2011. However the maximum speed is still only 80km/h.

JC-08, maxes out at 80 km/h

Plus, one needs to consider the fact that the largest segment in the Japan domestic car market are kei cars, microcars with engine capacity below 660cc with measurements no more than 3.39m in length, 1.48m in width and 2m in height. Their tiny engine meant that they hardly venture beyond 80km/h. Japanese legislators had to take this into consideration when drafting the law. It is not realistic to have two separate set of standards as manufacturers will then find a loophole within the legal framework to exploit. The advent of turbocharged kei cars boom in the 90s is one such example and this lead Japanese to legislators introducing cap on power output on kei cars by 1998. The Japanese parliament does not function like FIA, so they can't be reviewing automotive laws every year.  Governments shouldn't be changing laws every now and then. That would be like changing the size of a goal post in a football game played by car makers at every half time! These tiny kei cars are mostly used in highly urban metropolis areas and their average speed will hardly venture beyond 80 km/h. Anything above 80 km/h is beyond the optimal efficient operating speed for these engines, by which fuel consumption will increase rapidly for each km/h above the limit. Hence the maximum speed adopted by JC08.

European driving habits however, are very different from Japan. The highway speed limit in the UK is 70mph or 112 km/h but British drivers generally drive well above that, averaging at 85 mph or 137 km/h on highways. UK is also the largest car market in Europe. Germany, another major car market in Europe famed for its speed limit free autobahns (although in reality a large majority of stretches already have speed limit imposed) has an average autobahn driving speed of 130km/h.

The US however has a slightly more complicated fuel economy standards. The National Highway Traffic Safety Administration (NHTSA) reviews and determine the minimum standard for the Corporate Average Fuel Economy (CAFE) standard that all manufacturers must adhere to. Enforcement of this standard is done by the Department of Transport (DOT). However, neither the NTHSA nor DOT does any testing on its own but depends on another federal agency, the Department of Environmental Protection Agency (EPA) to do the testing. EPA testing methods however differ greatly from Japanese and European methods, which relies on fuel flow meters to determine the amount of actual amount of fuel used. The EPA on the otherhand, calculates the amount of fuel burned based on exhaust emission, using something called a exhaust gas analysis/carbon mass balance test. It is fairly straight forward process that removes the need to install any fuel / air flow metering device to the vehicle.

Unlike Japanese or European methods, EPA figures are derived from up to 5 different test conditions, involving not just speed but different ambient temperature and increased loan on air-conditioning. City driving figures are then adjusted downwards by 10% while highway are adjusted downward 22% to better reflect real world driving conditions where vehicle speed is not constant. The full details on the test method can be found here. Here is a good but lengthy article at Car and Driver covering on US EPA fuel economy test methods.


Test vehicle (Honda Insight shown) is strapped down, ambient temperature is set and stabilized.


Test driver "drives" according to a specific drive "schedule," guided by a computer monitor.


Collected data is then sent back to the control room.

So which is more accurate? Well that depends on your driving route as well as style, which of course is the other most important factor (other than the car) in determining fuel economy of any vehicle. And it's a bit hard to answer that question because there isn't any car sold in all 3 markets of Japan, Europe and USA under the same specs. They are all tuned differently to meet different fuel quality and emission standards. UK for example uses ordinary RON 91 to RON 98 while Japan uses RON 100, while US does not use RON rating. Emission regulations in US differ from state to state as well.