The RDE test verifies that vehicles maintain low emissions even under real road driving conditions. The RDE test does not replace but complements the WLTP laboratory test. During the RDE test, the vehicle is driven on the road in a wide range of different conditions. Conditions include different altitudes and temperatures, additional payload, uphill and downhill driving, urban roads (low speed), rural roads (average speed), highways (high speed).
In order to measure pollutant emissions while driving the vehicle on the road, test cars are equipped with portable measurement systems (PEMS) that provide full real-time monitoring of the main pollutants emitted by the vehicle. PEMS are complex devices that integrate advanced gas analyzers, exhaust gas mass flow meters, weather station, satellite-based geolocation and a network connection. The data collected is analyzed to verify that the boundary conditions of the RDE journey have been met and that emissions are within the limits of the regulation.
The limits not to be exceeded are defined as those prescribed in the laboratory test (WLTP) multiplied by compliance factors. Compliance factors shall take into account the margin of error of the instrumentation that does not measure at the same level of accuracy and repeatability as that used in the laboratory test.
The RDE test for passenger cars and light commercial vehicles of Class I applies to new type-approved models from 1 September 2017 and to all registrations from 1 September 2019 in case of nitrogen oxides (NOx) verification, with a compliance factor of 2.1. However, in the case of particle number (PN) verification, the compliance factor is 1.5 and applies to all registrations from 1 September 2018. For light commercial vehicles of Class II and III, the RDE test applies one year later.