Development of test cycle conversion factors among worldwide light-duty vehicle CO2 emission standards

Comparing the light-duty vehicle fuel efficiency standards in effect in the world’s largest auto markets is not a simple, straightforward process, because any fair, apples-to-apples comparison must account for differences in the test procedures that determine whether vehicles meet the standards or not. Of particular importance, the driving cycles specified by various regulations produce dissimilar engine loads and emissions.

This paper compares the dynamics of the four most important driving cycles and their impacts on fuel consumption and CO₂ emissions. The driving schedules include those specified in the three most relevant national regulations—the U.S. CAFE standards (a composite of FTP75 and HWFET), the New European Driving Cycle (NEDC), and Japan’s JC08—plus the recently developed Worldwide Harmonized Light-Duty Test Cycle (WLTC). CO₂ emissions were simulated over the test cycles for a variety of vehicle and technology packages using a vehicle emission model developed by Ricardo Engineering. Model runs based on the speed courses of the driving cycles were resolved on a second-by-second basis. Current vehicle architectures and advanced innovative technologies focusing on the 2020/2025 horizon were covered.

The outcome is a set of usable conversion factors to translate distance-based CO₂ emissions among the different driving cycles. These factors were determined on distinct levels of detail, characterized by technology parameters such as share of diesel engines in the fleet, vehicle size, share of hybrid systems, aerodynamic drag, and others.

This study updates and refines an earlier analysis completed in 2007. The table below summarizes key differences between the earlier and later analyses.

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