The biggest criticism of the old test method was the significant difference between emission measurements in the laboratory and in real driving situations on the road. So, in addition to and as a supplement to the new Worldwide harmonized Light vehicles Test Procedure (WLTP), the Real Driving Emissions (RDE) test was developed and introduced. In the RDE test, portable emission measuring systems (PEMS) are attached to the tested vehicle to check and confirm the emission values for nitrogen oxides (NOx) and particle numbers (PN) under real driving conditions.
The RDE legislation has been developed in four legislative acts that have been in force for several years. The European Commission chose this approach because of the broad and technical nature of the text, which covers various areas such as specifications for measuring devices, trigger definitions and boundary conditions.
The four packages were divided as follows: The first package (RDE 1), which was voted on in the Technical Committee of Motor Vehicles (TCMV) in May 2015 and published in the Official Journal of the European Union in March 2016, contains the basic definition of the actual test procedure. In the initial phase from the beginning of 2016, RDE tests were only carried out for monitoring purposes and had no impact on the actual type approvals, which continued to be issued on the basis of laboratory measurements.
The second package (RDE 2), which was voted on in October 2015 and published in the Official Journal of the European Union in April 2016, requires RDE measurements of NOx from September 2017 for new passenger car models and from September 2019 for all new vehicles.
The third package (RDE 3), voted on in December 2016, extends RDE testing to the measurement of particulate emissions (particle number) until September 2017 for all new vehicle models and until September 2018 for all new vehicles. The package also includes special legal requirements for hybrid vehicles and a procedure for including cold starts and regeneration events in the RDE test. In addition, the third package also made certification and registration of the results by manufacturers mandatory in order to ensure the necessary transparency.
The fourth package (RDE 4), which was voted on in May 2018 and has been in force since 1 January 2019, includes the new In-Service Conformity (ISC) test, which requires that emissions from vehicles already on the road must be checked each year by type-approval authorities. Type-approval authorities and the Commission may ask accredited laboratories to carry out a test. In addition, the fourth package contains an initial reduction in the conformity factor (1.50 to 1.43). This is to be reduced in stages to 1 by 2023 at the latest. Finally, the law includes a new methodology for assessing actual driving emissions and ensuring that vehicles are driven properly during such tests.
In addition, on 18 February 2020 the Joint Research Centre (JRC) of the European Commission published its assessment of the uncertainty of portable emission measurement systems (PEMS) for the years 2018-2019 compared to standard laboratory equipment in relation to real driving emissions (RDE).