Combined Fuel Consumption

1. Definition and Role

Combined fuel consumption refers to the weighted average fuel consumption of a vehicle measured under a specific test cycle that simulates various driving conditions, including urban low-speed, suburban high-speed, and rural roads, expressed in litres per 100 kilometres (L/100 km). Its primary function is to provide car buyers with a standardised benchmark close to day-to-day driving averages, allowing direct comparison of fuel economy between different vehicle models. This figure evolves alongside testing standards; while current testing standards have narrowed the gap between official figures and real-world fuel consumption compared to the older NEDC era, real-world discrepancies still exist due to varying test boundary conditions.

2. WLTC Combined Fuel Consumption

WLTC combined fuel consumption is the combined fuel consumption rating derived under the Worldwide Harmonised Light Vehicles Test Cycle (WLTC). Having superseded the legacy NEDC cycle, WLTC has become the most widely adopted international testing standard, covering four speed phases: Low, Medium, High, and Extra-High, spanning a total duration of 1,800 seconds and a test distance of 23.25 km. WLTC combined fuel consumption is significantly closer to real-world driving conditions than NEDC, serving as the benchmark standard for new vehicle energy consumption homologation in most countries today. China adopted the WLTC cycle for new vehicle fuel consumption certification in 2021; however, it is worth noting that the Chinese version excludes the Extra-High speed phase (from the original WLTP), while test protocols for energy-saving features (such as auto start-stop systems) also differ from the European version. These factors must be taken into account when cross-referencing WLTC figures between Chinese and international market models.

3. Evolution and Current Status of Test Cycles in China

• NEDC Combined Fuel Consumption (Phased out for new vehicle homologation) : Comprising four urban driving cycles and one extra-urban cycle, with an average speed of 34 km/h over a 1,180-second duration. Test parameters were overly lenient—lacking hard acceleration and air-conditioning load—leading to a considerable disparity with real-world driving. Often dubbed an "ideal laboratory figure", it was typically 15% to 25% lower than actual fuel consumption.

• WLTC Combined Fuel Consumption (Current certification standard) : Replaced NEDC as China's official energy consumption rating standard for new vehicles. With test cycles reflecting real-world driving more accurately, figures are much closer to what drivers experience on the road. According to comparative data from the Ministry of Industry and Information Technology (MIIT) and third-party bodies, WLTC combined fuel consumption is generally 10% to 15% higher than NEDC, offering a realistic benchmark for average real-world driving.

• CLTC Combined Fuel Consumption: Developed specifically for Chinese road conditions and traffic patterns, the CLTC cycle features a top speed of 114 km/h and an average speed of 28.96 km/h. It is primarily utilised for evaluating the range of pure electric vehicles (EVs) and is seldom applied to internal combustion engine (ICE) vehicles.

4. Composition and Calculation of Combined Fuel Consumption

Combined fuel consumption is not a simplistic arithmetic mean of urban and extra-urban figures; it is calculated using predetermined mileage weighting:
Combined Fuel Consumption = (Urban Fuel Consumption × Urban Mileage Weighting) + (Extra-Urban Fuel Consumption × Extra-Urban Mileage Weighting)
Under WLTC, each of the four speed phases carries distinct mileage weightings, with the Low and Extra-High speed phases exerting a particularly pronounced effect on the final combined figure.

5. Future Trends

• Stricter Testing Standards: Following the full rollout of the WLTC cycle in China, official combined fuel consumption ratings have aligned far more closely with real-world driving performance.

• Stricter Regulations on NEVs and Hybrids: Fuel consumption for plug-in hybrid electric vehicles (PHEVs)—specifically Condition B / charge-sustaining fuel consumption—is increasingly coming under regulatory scrutiny, with national policies progressively tightening combined fuel consumption thresholds.

• Consumer Awareness and Education: With ongoing improvements to fuel economy labelling regulations, consumers now have a clearer grasp of the variance between official ratings and real-world fuel economy. All new vehicle fuel economy labels are mandated to display "combined cycle" data for reference.