Characterisation of real-world CO2 variability and implications for future policy instruments

There is increasing evidence suggesting that real-world fuel consumption and CO2 emissions improvements in the last decade have been much lower than the officially reported ones. Scientific studies show that the offset between officially reported values and real-world vehicle CO2 emissions in Europe has constantly increased over the last years. The difference between officially reported and actual CO2 emissions of vehicles has three main implications: a) it undermines the collective effort to reduce greenhouse gas emissions in Europe, b) it creates an unfair playing field for different competitors, and c) it affects the credibility of vehicle manufacturers. As a fundamental step to deal with this issue the European Commission has replaced the old and outdated NEDC test procedure used so far in the emission type-approval of vehicles by the Worldwide harmonized Light vehicles Test Procedure (WLTP). Being a lab-based test-procedure, the WLTP, by its nature, can only cover part of the CO2 gap. Some stakeholders have suggested that the remaining gap could be tackled by additional measures based on real-world measurements. The objective of the present report is to analyse possible ways to deal with the remaining CO2/fuel consumption gap. In particular, fleet-wide monitoring of real-world fuel consumption and model-based tools able to provide customized information to road users are the measures suggested. In addition, the paper presents experimental evidence on the variability of the CO2/fuel consumption of vehicles, putting into question the idea that a single central estimate of these quantities may be sufficient.