Including cold-start emissions in the Real-Driving Emissions (RDE) test procedure : an assessment of cold-start frequencies and emission effects

We document two independent analyses that were conducted to support the inclusion of cold-start emissions in the Real-Driving Emissions (RDE) test procedure. First, we present the results of a scoping review on cold-start frequencies and trip distances in Europe. Second, we present a scenario analysis that aims to quantify the impact of modifications in the RDE data pre-processing and evaluation on the calculated NOX emissions over the urban part of an on-road test. We find that some 27 ± 5% of trips in Europe may contain a cold start. The driving distance between two consecutive cold starts reaches 36 ± 16 km (mean) and 30 ± 13 km (median), respectively. Our scenario analysis suggests that a simple inclusion of cold start into the regulatory RDE data evaluation procedure may not capture cold-start NOX emissions in a robust manner. However, combining modifications of the RDE data pre-processing and the RDE data evaluation can capture at least part of the incremental cold-start NOX emissions. A more systematic assessment of European driving data and an expansion of the scenario analysis presented here could substantiate the findings of this report.