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WLTP and RDE tests for measuring emissions come into force in EU tomorrow

Two new tests for measuring emissions from cars and vans will come into force in the EU tomorrow. The new laboratory test, the Worldwide Harmonized Light Vehicle Test Procedure (WLTP), will introduce more realistic testing conditions for measuring pollutant and CO2 emissions than the previous, outdated lab test (NEDC). It thus provides a more accurate basis for measuring a vehicle’s fuel consumption and emissions.

The real driving emissions (RDE) test, which measures pollutant emissions on the road, also applies as of tomorrow, making Europe the only region in the world to implement such mandatory testing. Under RDE, a car will be driven on public roads over a wide range of conditions using portable measuring equipment (PEMS). RDE will complement WLTP to ensure that pollutant emission levels, measured during the laboratory test, are confirmed on the road.

WLTP. A Global Technical Regulation (GTR) on WLTP was developed and finally adopted by UNECE’s World Forum for Harmonization of Vehicle Regulations in March 2014, at the request of policy makers, the automobile industry and consumers. However, GTRs require incorporation into national or regional legal frameworks before they can be applied.

As of 1 September, WLTP will apply to all new car types (models that are introduced on the European market for the first time). One year later, in September 2018, WLTP will apply to all new cars registered.

The old NEDC test determines test values based on a theoretical driving profile; the WLTP cycle was developed using real-driving data and better represents everyday driving profiles.

Start temperature Cold Cold
Cycle time 30 min. 20 min.
Stationary time proportion 13 % 25 %
Cycle length 23.25 km 11 km
Speed Average: 46.5 km/h – Maximum: 131 km/h Average: 34 km/h – Maximum: 120 km/h
Drive power Average: 7.5 kW – Maximum: 47 kW Average: 4 kW – Maximum: 34 kW
Influence of optional equipment and air-conditioning (AC) Optional equipment is taken into account for weight, aerodynamics and VES requirements (no-load current). No AC Not considered at present

The WLTP test cycle closes many of the loopholes in the NEDC test procedure, making it more difficult for car manufacturers to optimize test results at the cost of real fuel efficiency and pollutant emissions such as particles and NOx. It was the manipulation of the emissions test and its results that was at the center of the 2015 emissions scandal, which involved a number of car manufacturers. It is estimated that fuel consumption figures using WLTP will be 10 to 20% higher than those under NEDC.

The WLTP driving cycle will be divided into four parts with different average speeds: low, medium, high and extra high. Each part contains a variety of driving phases, stops, acceleration and braking phases. For a certain car type, each powertrain configuration is tested with WLTP for the car’s lightest (most economical) and heaviest (least economical) version.

WLTP was developed with the aim of being used as a global test cycle across different world regions, so pollutant and CO2 emissions as well as fuel consumption values would be comparable worldwide. However, while the WLTP will have a common global core, the European Union and other regions will apply the test in different ways depending on their road traffic laws and needs.

While WLTP greatly improves the accuracy and consistency of test results, it is still a laboratory procedure designed to facilitate repeatability and reproducibility of the test. The EU will be using WLTP to complement the EU’s Real Driving Emissions (RDE) testing, which is performed on-road. The World Forum is now considering the incorporation of RDE testing within its international regulatory framework.

RDE. RDE step 1 (with a NOx conformity factor of 2.1) will also apply as of 1 September for new car types. It will apply in September 2019 for all types. RDE step 2 (with a NOx conformity factor of 1.0 plus an error margin of 0.5) will apply in 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 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 European Automobile Manufacturers’ Association (ACEA) said that it welcomed the two new tests for measuring emissions from cars and vans. ACEA also welcomed the fact that with RDE there is now one common EU-wide test to measure on-the-road emissions of cars. ACEA said that this should help prevent the confusion caused by using a multitude of different tests, each with varying and incomparable methods and results.



“About time”, one could say, when we note that the public opinion seems to have wanted this for a very long time. People in general do not understand that it is a very long process before a new regulation can come into force. As I can recall, work on the WLTP test cycle has been going on for at least for 10 years and the process for RDE was almost as long. RDE has noting specifically to do with the VW scandal but it might have had a minor impact on the process most recently. For sure, this has justified the complex - and expensive - RDE testing; no debate about that any more.

On the background on what EU has done, we can see the US EPA will still continue to use a test procedure that was conceived in the 1970’s. The old FTP cycle has little resemblance with modern driving style, yet EPA will still use it at least to 2025. This is stunning, since USA has participated in this work. The basic idea with “Worldwide Harmonized…” was that it would be used… around the globe. But perhaps the main idea as to why EPA has not adopted WLTP is some kind of protectionism or an act to favor US auto industry. Not invented here…

The first thing that will be immediately noted is that fuel consumption in the WLTP will be closer do “real-world” fuel consumption. Yet one should note that “real-world” fuel consumption is different for every customer. “Worldwide Harmonized” also means that the test cycle is a compromise between different driving styles around the world. Nevertheless, comparisons between cars will be more realistic in WLTP.

On the long run, RDE will decrease “real-world” emissions and thus, improve ambient air quality. It will also make competition more “fair” and close a couple of loopholes. This is by no means the end of the development. The next step will most likely be much simplified RDE tests where sensors will be used instead of advanced laboratory instruments. This would enable more tests at a significantly lower cost, i.e. more cost-effective testing. Work is already going on in this field and tests are promising. The third step could be that such sensors are permanently mounted on cars and log emissions for long periods, i.e. weeks or months. Data will be sent wireless to a server for “big data” analysis. The fourth and (perhaps) the final step could be that such sensors are integrated in the engine emission control system and used for OBD/OBM/OBS, or whatever you would like to call it.

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