From lab-to-road: real-world fuel consumption and CO₂ emissions of plug-in hybrid electric vehicles

Plug-in hybrid electric vehicles (PHEVs) combine an electric motor with an internal combustion engine and can reduce greenhouse gas emissions from transport if mainly driven on electricity. The environmental benefit of PHEVs strongly depends on usage and charging behaviour. However, there is limited evidence on how much PHEVs actually drive on electricity and how much conventional fuel they use in real-world operation. Here, we provide the first systematic empirical analysis of real-world usage and fuel consumption (FC) of approximately 100 000 vehicles in China, Europe, and North America. We find that real-world mean CO₂ emissions of PHEVs are between 50 and 300 g CO₂ km⁻¹ depending on all-electric range, user group and country. For private vehicles, real-world CO₂ emissions are two to four times higher than test cycle values. The high CO₂ emissions and FC mainly result from low charging frequency, i.e. less than once per driving day. Our results demonstrate the importance of real-world vehicle emission measurements and indicate the need to adjust current PHEV policies, i.e. official emission values need to better reflect realistic electric driving shares and incentives need to put more emphasis on frequent charging. (letter)