The exhaust emissions of two Euro 6 diesel cars with different emissions control systems have been evaluated both on the road and over various chassis dynamometer test cycles. European emissions limits are currently set using the New European Driving Cycle (NEDC), but the European Commission is preparing additional test procedures to ensure that emissions are well controlled both in real-world use and over the legislative test cycle. The main focus of this work on ‘Real Driving Emissions’ (RDE) is on measurements using Portable Emissions Measurement Systems (PEMS) in truly representative, on-road, driving. A key focus of the test programme, undertaken as a collaboration between AECC (the Association for Emissions Control by Catalyst) and Ricardo UK, was therefore the use of PEMS systems to measure on-road emissions of both gaseous pollutants and particulate matter. This included measurement of particle number emissions with a new candidate system for this type of measurement.The results from this testing are compared with emissions measured over four different chassis dynamometer test cycles - the current legislative cycle (New European Driving Cycle, NEDC); the Common Artemis suite of test cycles (CADC) that is widely used in emissions modelling; the new Worldwide Light-duty Test Cycle (WLTC) defined by the UN Working Party on Pollution and Energy (GRPE) as part of the development of the Worldwide harmonised Light vehicles Test Procedure (WLTP); and a set of cycles produced by a Random Cycle Generator based on ‘short trip’ segments from the EU database used to construct WLTC. This Random Cycle (RC) approach was originally considered by the European Commission and Member States as an alternative to PEMS measurements, but remains an option for particle number measurement should PEMS instrumentation not be fully available by the time such measurements are required by legislation.The aim of this test programme was to evaluate the emissions performance of two different vehicles when using PEMS systems in real-life driving, and to identify and help understand the differences in emissions that may arise between the various test procedures. The test results show the differing vehicle emissions performances that may be encountered in real-driving for two vehicles that both meet the Euro 6 limits in Type-Approval laboratory testing. The results show that in some cases the on-road PEMS-measured emissions for complete test routes can exceed Type-Approval limits, and indicate that real-world conditions require more robust control strategies over those needed to satisfy existing legislation.