Which factor contributes more to the fuel consumption gap between in-laboratory vs. real-world driving conditions? An independent component analysis

A widening vehicle fuel consumption gap has been found between in-laboratory and real-world driving conditions, which can undermine policy-making concerning energy saving and greenhouse gas reduction. Various factors have been identified as contributors to the gap; however, their contributions have not been independently assessed, which hinders the gap's narrowing. This study confirmed an average gap of 42% based on 0.95 billion records of second-by-second vehicle operating (speed, acceleration, etc.) and fuel consumption data collected from 395 light-duty vehicles through On-board Diagnostics (OBD) devices in Beijing. Contributions of fuel consumption rate (FCR)-related, engine load-related, and road grade discrepancies between the in-laboratory test procedure vs. real-world driving conditions to the gap were independently assessed. Results indicated that the FCR-related, engine load-related, and road grade discrepancies contributed 20.7%, 17.0%, and 3.2% to the gap, respectively (only 1.0% of the gap has not been explained). Replacing the test cycle from the New European Driving Cycle (NEDC) with the China Light-duty vehicle Test Cycle (CLTC-P) has the potential to reduce the engine load-related gap from 17.0% to 6.9% in Beijing. Policies should focus on developing more local test procedures or recording real-world fuel consumption through onboard devices to evaluate vehicle economy with higher reality representation.