How accurately can we measure vehicle fuel consumption in real world operation?

European Union (EU) regulations setting CO2 emission standards for light-duty (LDV) and heavyduty vehicles (HDVs) require the Commission to monitor in-use fuel consumption (FC) using onboard fuel consumption monitoring (OBFCM) devices. For LDVs, the accuracy to measure fuel consumed is set by regulation to +/- 5%, while for HDVs no requirements exist so far. In this study, OBFCM data from 15 LDVs and 12 HDVs were recorded in lab and on-road trips. Results indicate that the fuel consumed measured by the OBFCM, for the majority of the vehicles, satisfies the accuracy requirements of +/- 5% over complete laboratory tests or complete on-road trips (maximum vehicle average uncertainty similar to 7%). Statistical analysis showed that on-board diagnostics (OBD) accuracy can be impacted by the average vehicle speed, acceleration, and overall trip dynamicity. The lowest accuracy can be expected when vehicles are driven at low speeds under transient conditions. For most of the vehicles the distance calculated from the OBD speed signal has an accuracy within +/- 1.5% on-road when Global Positioning System (GPS) distance is used as a reference. Both HDV and LDV results, confirmed that OBD accuracy and precision in measuring fuel consumed and distance improved for monitoring over longer periods (complete trips vs short phases). The results of this study could be used to further support the standardization of OBFCM accuracy in vehicles, and the setup of the EU real-world CO2 emissions monitoring approach.

Automated summary

This study recorded on-road and lab trips data of LDVs and HDVs using OBFCM devices, showing that most vehicles met the accuracy requirements of +/- 5% with a maximum uncertainty of around 7%. OBD accuracy can be influenced by average vehicle speed, acceleration, and trip dynamicity, improving over longer monitoring periods.