This report aims to give insight in the design of policies to further reduce passenger car emissions after 2020. The EU has set emission targets for new cars up to 2020 and is now preparing the post-2020 legislation. Maximizing both efficiency and overall CO2-performance of all vehicle types (internal combustion engine, electric, and hydrogen) will be complicated to achieve with a single CO2-based standard. At the time the report was published, an efficiency-based standard was more effective and might offer additional benefits. The report provides basic directions for how such legislation could be shaped.