Fuel consumption and CO 2 emissions from passenger cars in Europe – Laboratory versus real-world emissions

Official laboratory monitoring data indicate a progressive decline in the average fuel consumption and CO2 emissions of the European passenger car fleet. There is increasing evidence to suggest that officially reported CO2 values do not reflect the actual performance of the vehicles on the road. A reported difference of 30-40% between official values and real-world estimates was found which has been continuously increasing. This paper reviews the influence of different factors which affect fuel consumption and CO2 emissions on the road and in the laboratory. Factors such as driving behavior, vehicle configuration and traffic conditions are reconfirmed as highly influential. Neglected factors (eg side winds, rain, road grade) which may have significant contributions are also identified. Results show that the certification procedure margins can account between 10-20% in the gap between the official values and reality which was estimated to be in the order of 40% (47.5gCO2/km) but could range up to 60% or down to 19% depending on traffic conditions. The introduction of a new test protocol is expected to bridge about half of the present divergence between laboratory and real world. Despite the substantial research found on the topic a lack of common test procedures, analysis tools and methods and most importantly coordinated activity across different countries has been identified. Additional research is needed in order to accurately reproduce real world vehicle operation and propose targeted actions for CO2 reduction. In-use fuel consumption monitoring could be used in order to assess the gap on a continuous basis.