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.JRC.C.4-Sustainable Transpor

The monitoring and reporting of CO2 emissions of light duty vehicles in Europe and other major markets is based on the New European Driving Cycle and the accompanying test protocol. This procedure has been proven non-representative of real world vehicle operation, fuel consumption and CO2 emissions leading to a gap between officially reported emissions and the ones experienced during real world operation. This gap is reported to be increasing with time. To address this issue and improve the certification procedure for pollutant emissions of vehicles over real driving, the new Worldwide Harmonized Light duty vehicle Test Protocol was designed. This new test procedure is expected to provide more realistic emission and fuel consumption results. In this paper a first estimate of the certification-reality gap under the present (2015) conditions is attempted and the impact of the new test procedure is investigated. Tests were performed on three real vehicles over the two cycles which allowed the development of representative simulation models. A detailed simulation matrix was subsequently formulated, taking into account the two tests and expected conditions occurring during real world driving. Results show that for 2013-14 model year European passenger cars the difference in certified and actually emitted CO2 emissions for an average European passenger car reaches up to 40 g CO2/km (~32% higher than certification). WLTP introduction is expected to improve the picture, however a shortfall of about 10-15% between official and real world may remain.JRC.C.4-Sustainable Transpor