The Real Driving Emissions (RDE) test measures the pollutants, such as NOx, emitted by passenger vehicles while driven on the road. RDE does not replace the WLTP laboratory test, but complements it. RDE ensures that passenger vehicles deliver low emissions over on-road conditions. Europe is the first region in the world to introduce such on-road testing, marking a major leap in the testing of car emissions.

Under RDE, a vehicle is driven over a wide range of real world driving conditions. Specific equipment installed on the vehicle collects data to verify that legislative caps for pollutants such as NOx are not exceeded.
Conditions include: 
• Low and high altitudes
• Year-round temperatures 
• Additional vehicle payload 
• Up- and down-hill driving 
• Urban roads (low speed)

To measure pollutant emissions as the vehicle is being driven on the roads, vehicles are fitted with Portable Emission Measuring Systems (PEMS) that provide a complete real-time monitoring of the key pollutants emitted by the vehicle (i.e NOx). 
The PEMS used for regulated emissions are complex pieces of equipment that integrate advanced gas analysers, exhaust mass flow meters, weather station, Global Positioning System (GPS) and a connection to the vehicle networks. 
There is no ‘standard’ PEMS equipment and equipment manufactured by different suppliers will always deliver slightly different results. The collected data is analysed to check that the RDE trip boundary conditions were achieved and that the emissions were within acceptable levels.

RDE step 1 (with a NOx conformity factor of 2.1) has applied since 1 September 2017 for new car types. It applies to all types as from September 2019. 
RDE step 2 (with a NOx conformity factor of 1.0 plus an error margin of 0.5) applied from January 2020 for new types and then from January 2021 for all types.

A conformity factor is defined as a ‘not to exceed limit’ that takes into account a margin for error, which is present simply because the PEMS equipment does not deliver exactly the same results for each test. For example, PEMS are not as accurate as a full laboratory system so they will not measure to the same level of repeatable accuracy as a lab test. In practice, car manufacturers must set their design objectives well below the legal limit to be certain of complying.

The amount of CO2 a car emits is directly related to the amount of fuel/energy it consumes. For instance, a diesel car emitting 95g CO2 per kilometre consumes around 3.7 litres of fuel per 100km, while a petrol car consumes around 4 litres/ 100km for the same CO2 emissions. Fuel/energy efficiency, sometimes referred to as fuel/energy economy, is the relationship between the distance travelled and the fuel/energy consumed.

The CO2 emissions figure is used to determine the cost of Vehicle Excise Duty (‘car tax’) for new passenger vehicles during their first year of registration, in addition to any Company Car Tax. For those passenger vehicles approved under WLTP, a figure equivalent to what would have been achieved had the car been tested under NEDC has been used for taxation purposes – this is known as the NEDC equivalent value. From the 1st April 2020 (6th April for BIK), the CO2 value obtained under WLTP will be used instead of the NEDC equivalent. When WLTP does start to be used to calculate vehicle tax, it will only affect passenger vehicles that at that time are unregistered, i.e. the CO2 figure that is used for tax purposes when the car is first registered will not change during its lifetime.

The new WLTP testing regime is still a laboratory-based standardised test but it seeks to provide more realistic testing conditions and a more accurate basis for assessing a vehicle model's fuel/energy consumption and emissions figures. In essence, the aim is to ensure that test conditions better reflect real world driving.

No. At present no changes to the model portfolio are planned, however certain engine and gearbox combinations will change. Individual models and their engines will have to be further engineered in order to achieve even higher efficiency and reduce emissions as per the regulations. However, models will not be discontinued as a result of WLTP.

Yes, there are. The driving cycles for exhaust and consumption measurement developed in Japan (JC 08) and the USA (FTP 75) are more closely oriented on specific situations on the country’s roads. For example, Japan’s driving cycle includes numerous stop-and-go phases and is carried out twice, once as a cold start and once as a warm start.

Yes, electric vehicles are also tested according to the WLTP rules.

From 1st January 2019, energy efficiency labels displayed alongside vehicles in showrooms, show a range of WLTP values for fuel/energy consumption (low, medium, high, extra high and combined) and a combined NEDC equivalent value (derived from the WLTP test) for CO2.