We document two independent analyses that were conducted to support the inclusion of cold-start emissions into the Real-Driving Emissions (RDE) test procedure: (i) a scoping review of cold-start frequencies and trip distances in Europe and (ii) a scenario analysis quantifying the effect of modifications in the RDE data pre-processing and evaluation procedures on the calculated NOx emissions during 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 normal RDE data evaluation may not capture cold-start NOx emissions in a robust manner. However, combining modifications of the RDE data pre-processing and 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 preliminary findings of this report.
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Martin et al. (2017) studied this question.