This briefing summarises the important lessons for design of future EU vehicle regulations that have been concluded from an extensive programme of more than 400 real world car tests. The tests have been performed on Peugeot Citroën Group (PSA) cars as part of programme conducted by PSA in collaboration with Transport & Environment, France Nature Environnement and Bureau Veritas. The purpose was to provide PSA customers with reliable real world information on fuel economy and emissions. The views expressed in this briefing are solely those of T&E, but a technical report agreed by PSA and T&E has already been published presenting the comprehensive data.