What you see and what you get: fuel efficiency

Do you trust entirely the fuel efficiency numbers reported by automakers for every model they put on the market? Or do you suspect the real-world performance would be somewhat worse? The inconsistency between theoretical values and actual fuel consumption is a common issue which sparks a lot of debate in auto industry. In a recent research paper, scholars Maya Ben Dror, Lanzhi Qin and Feng An tried to quantify this discrepancy on the China auto market — and found it alarmingly high.

Older (left) and newer (right) standard designs for fuel efficiency stickers put on new cars

Let’s begin with brief description of Chinese national standards on fuel efficiency. State authorities rolled out “Light vehicle fuel consumption test method” (GB/T19233–200) in November 2004. This standard essentially copies the European Union test procedures (2004/EC/3). Some conditions of the test clearly skew fuel consumption to the lower side, for example:

While official testing procedures may diverge substantially from real-world car use, at least there is a strict standard followed by certification centers, which guarantee a certain degree of comparability. On the other hand, gathering fuel efficiency data from actual car owners always was a difficult and costly task.

Maya Ben Dror et al. decided to circumvent the associated issues by turning to the data gathered by a popular smartphone app, BearOil. This relatively simple app let Chinese car owners to track their odometer readings and fuel costs. Certainly, the accuracy of this approach is nowhere near traditional methods (like emissions measurement systems). But BearOil offers over 45 million fuel consumption data points from 1,167,915 car owners for over 17,000 models; and these numbers are impossible to achieve using established measurement practices. Of course, the researchers made their best effort to clean the dataset from misleading and unreliable records.

The result of their analysis shows staggering gap between manufacturers’ fuel efficiency values and real-world consumption. And this gap only worsened from 2008 to 2017.

Official average efficiency numbers declined smoothly, conforming to state policy of gradual tightening of fuel efficiency requirements. The average certified consumption was 7.99 L/100 km in 2008 and decreased 15% to 6.77 L/100 km in 2017. But for drivers, this decline remains almost virtual, as they do not burn less fuel per km in newer cars! The gap between certified and actual numbers existed in 2008, the first year of the analysis, being at 0.58 L/100 km. In 2017, it increased to 1.8 L/100 km, or hefty 27% of the official average number.

Next, the researchers looked at the differences between cars with a shift stick and cars with automatic transmission. The proportion of AT vehicles in national sales increased from 32.8% in 2008 to 68.8% in 2017.

Fuel efficiency gap for cars with different types of transmission

They found the official numbers for autos with AT were consistently less adequate than for MT vehicles. Both show worsening dynamics though. In 2017, cars with AT consumed 32% more fuel than their specs suggested.

The increase of the gap between official and owners’ data was universal for every vehicle type. MPVs, which make up about 9% of China auto market, enjoy the smallest divergence from certified numbers, at 21%. Medium-sized cars were hit hardest by the problem, with their owners reporting 34% worse fuel efficiency than claimed by manufacturers.

The analysis also considers different weight classes for vehicles. China fuel efficiency standards set strict limits for each weight class. Compliance is necessary for selling specific models on the national market. The researchers compared the real-world performance of cars in most popular weight classes with their respective efficiency limits and got a troubling picture:

For every weight class in the range 1,090–1660 kg, the owners-reported fuel efficiency was above the allowed limit. But more pain lies ahead: the blue lines represent 2020 government targets which now look absolutely unrealistic.

Unless the government will keep to adhere to its increasingly useless testing schemes and targets that only remain on paper, turning a blind eye to growing discrepancy between nice-looking official data and lack of progress in actual vehicles fuel efficiency — which would be perfectly familiar tactics for Chinese authorities. Distorted, inadequate fuel efficiency data benefit no one, including the government itself. Despite some positive image for achieving set goals, continuing with misleading standards masks real problems, inhibits necessary policy decisions, creates atmosphere of mistrust between consumers, producers and authorities, and only worsens environmental impact.

As of now, there is no legally defined accountability for misrepresenting fuel efficiency numbers in certification process. The situation is deteriorating too quickly, prompting all sorts of questions about the prudency of participating entities. While it’s too early to make any conclusion, the research highlights the need to review the national fuel efficiency policies and certification standards to enhance their practical value.

These problems are not unique for China, as Dieselgate clearly shows. And it’s not the case with Volkswagen only: an earlier work by Tietga et al. shows even wider difference between real-world and official efficiency in Europe: 42%. There is definitely much to be done to close this gap.

All illustrations are taken from: Ben Dror, M., Qin, L., & An, F. (2019). The gap between certified and real-world passenger vehicle fuel consumption in China measured using a mobile phone application data. Energy Policy, 128, 8–16. doi:10.1016/j.enpol.2018.12.039



I write on economics and future trends.

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