From laboratory to road international: A comparison of official and real-world fuel consumption and CO2 values for passenger cars in Europe, the United States, China, and Japan

Published: 2017.11.05
By

Uwe Tietge, Sonsoles Díaz, Zifei Yang, Peter Mock

This study investigates the gap between real-world and official CO2 emission values in the four largest vehicle markets in the world: China, the EU, Japan, and the United States. The analysis shows that the gap has increased in all markets since 2001. The EU saw the largest increase in the gap while the United States saw the lowest increase. China and Japan placed in the middle in terms of growth. Japan stands out with the highest gap level.

The U.S. Environmental Protection Agency’s so-called label values, which are designed to represent real-world conditions, offered the most realistic fuel consumption figures in the analysis, with virtually no gap at all in 2014. These label values show that it is possible to produce realistic point estimates of fuel consumption that, on average, match what consumers experience on the road.

The ICCT monitors the gap between real-world and official CO2 emission values of new European passenger cars in the From Laboratory to Road series. This study extends the analysis beyond the borders of Europe, yielding a number of valuable policy insights.

A side-by-side comparison of policies and divergence estimates highlights some aspects that are key to effective fuel efficiency standards:

  • Independent retesting: Independent retesting of laboratory measurements was identified as a best practice. All markets have some form of compliance program in place, but the United States has the most extensive program, covering the full lifetime of vehicles by verifying coastdown measurements, testing production-line vehicles, and conducting in-use surveillance tests.
  • Policy enforcement: The comparatively low growth in the U.S. gap indicates that stringent policy enforcement, such as levying penalties on manufacturers that misstate fuel economy values, acts as a deterrent to gaming. In contrast, the EU has seen the largest growth in the gap from 2001 to 2014 and lacks a central authority to issue vehicle recalls and to impose financial penalties.
  • Real-world standards: CO2 and fuel economy standards should be based on test values that, on average, correspond to real-world measurements. Policies that fail to account for the divergence will overestimate fuel savings and climate change mitigation benefits. Using an adjustment factor to approximate on-road values, as is done in the United States, is an approach that does not require extensive overhauls of vehicle testing procedures to account for real-world CO2 emissions. Other approaches for measuring on-road emissions is using portable emissions measurement system equipment. More realistic test cycles and more rigorous procedures for laboratory testing could also furnish more realistic CO2 values.
  • Real-world measurements: Measuring real-world fuel consumption is a key recommendation because these data are needed to evaluate the efficacy of CO2 and fuel economy standards. Bulk on-road fuel consumption data can be measured using web services. As the only government-run example of such services, the MyMPG tool on FuelEconomy.gov stands out as a best-practice example. These data can be used to estimate fleet-wide real-world CO2 emission values and gauge policy impacts. Using data loggers connected to vehicles’ on-board diagnostics ports is another option for real-world fuel consumption data collection. The growing divergence between official and on-road CO2 emission values is troubling because it represents a decoupling of regulated metrics and real-world impacts. Recommendations presented in this study illustrate that solutions are available to close or at least manage the gap.

The growing divergence between official and on-road CO2 emission values is troubling because it represents a decoupling of regulated metrics and real-world impacts. Recommendations presented in this study illustrate that solutions are available to close or at least manage the gap.