From laboratory to road: Modeling the divergence between official and real world fuel consumption and CO2 emission values in the German passenger car market for the years 2001-2014

Official fuel consumption and carbon dioxide (CO2) emission values of European passenger cars are widely recognized to be unrepresentative of real-world driving. The divergence between official and real-world values undermines national vehicle taxation schemes and EU-wide CO2 standards for passenger cars, particularly since the divergence increases with new model generations. This study examines real-world fuel consumption data from more than 130,000 vehicles to investigate the development of the divergence. The analysis validates and refines a regression model developed by Ntziachristos et al. (2014), which estimates real-world fuel consumption of cars based on readily available vehicle characteristics, namely official fuel consumption values, vehicle mass, and engine capacity. The regression model yielded coefficients of determination of 0.87 or higher, but was found to underestimate fuel consumption of newer vehicles and company cars. This study proposes to add vehicle build year as a regressor to account for the increasing divergence between official and real-world fuel consumption figures.