Dealing with the Gap between Type-Approval and In-Use Light Duty Vehicles Fuel Consumption and CO 2 Emissions: Present Situation and Future Perspective

Abstract

There is increasing evidence suggesting that real-world fuel consumption and CO₂ improvements in the last decade have been much less than those measured during type-approval tests. Scientific studies have found 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: (i) it undermines the effectiveness of CO₂ regulations in reducing greenhouse gas emissions in Europe; (ii) it distorts competition between vehicle manufacturers; (iii) it undermines innovation. As a fundamental step to deal with this issue, the European Commission has already replaced the old and outdated test procedure used so far in the emission type-approval of vehicles with the worldwide harmonized light vehicles test procedure (WLTP).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. There is therefore increasing pressure to integrate the current type-approval system with additional measures based on real-world measurements. One of the options under discussion is to use the CO₂ emissions measured during the real driving emission test. The objective of the present paper is to assess the validity of this proposal and to propose other possible ways to deal with the CO₂/fuel consumption gap. In particular, the paper presents experimental evidence on the variability of the CO₂/fuel consumption of a vehicle, questioning the idea that a single central estimate of these quantities may be sufficient.