RDE test. Part III: Measurement of emissions in real road traffic.

"What matters is what happens on the pitch" – or so goes a footballing expression. When it comes to the measurement of emissions, read "road" for "pitch". That's why the WLTP laboratory measurement is supplemented by the so-called RDE (Real Driving Emissions) test.

For the test, the vehicles are equipped with a so-called PEMS (Portable Emission Measurement System) for mobile emissions measurement. The actual measurement is performed in Germany by, among others, a Technical Service (TÜV or similar). In future, however, it is planned that field measurements for the type approval authority can also be carried out by accredited third parties authorized to officially report the results as a field test.

The limits:

These are legally prescribed by the Euro 6d TEMP standard. At first glance, there is no change to the limits for nitrogen oxide (NOx) emissions of 80 mg/km for diesel vehicles and 60 mg/km for gasoline vehicles in comparison with Euro 6a, b, c. However, Euro 6d TEMP additionally requires an RDE measurement on the road. This will take place in two phases.

• In the first phase, which began on September 1, 2017, a vehicle must demonstrate on the road that it does not emit more than 2.1 times the legal NOx limit for the laboratory test or 1.0 times the particulate emissions (PN) plus a measuring tolerance of 0.5. However, that is an upper limit – our in-house goal is that all our vehicles should be well below this "No Exceed" limit.

• From 2020/2021, also for nitrogen oxides (NOx), the "on-road value" must no longer exceed the laboratory limit – there will still be a maximum measuring tolerance of 0.5 of the laboratory limit. But this tolerance will be annually reviewed by the EU Commission with a view to its being lowered.

The measuring method:

The measurement relates to nitrogen oxide (NOx) and particulate emissions (PN), which are each subject to a limit, as well as carbon monoxide (CO), which is subject to compulsory monitoring. No detailed cycle is defined. Driving and measuring take place in real everyday traffic – always, of course, in accordance with the road traffic regulations. The route, however, must meet defined general conditions, which guarantee that the test drive includes statistically relevant driving maneuvers as well as road/weather conditions:

The timeline: What vehicles are covered by RDE? And from when?

• In the first phase, since September 1, 2017, RDE applies to newly certified vehicle models. In simple terms this means: a manufacturer's all-new model variants that are being certified for the first time before going onto the market. These are described as New Types (= NT).

• From no later than September 1, 2019, it will apply to all new vehicles. In simple terms this means: all a manufacturer's new-vehicle models that are in production and already on the market.

RDE, together with the new WLTP test cycle, will result in significantly more realistic consumption and emissions values. But what is relevant especially from the customer's viewpoint: Even the RDE emissions figures will not reflect average real driving, because that's something that simply doesn't exist. Both the route profile as well as the payload and driving style constitute individual parameters that render a representative, average value for every driver impossible.

Practical tip:

The RDE results for Mercedes-Benz vehicles, which were measured both by us as the manufacturer and by independent, state-approved Technical Services [CHECK], can be viewed on the Mercedes-Benz website on the Internet .

To summarize: What applies from when? And to what vehicles?

With regard to all applicable dates for the new standards, a distinction is made in terms of scope of application between "New Types" and a manufacturer's total portfolio of new vehicles (cars), which is described as "All Types":

• New Type (NT): A new product project or a facelift, i.e. a vehicle that is being certified for the first time.

• All Types (AT): An existing model series that is already in production and still on sale in showrooms as new vehicles. This does not include used vehicles or new cars that are already with customers. Consequently, New Types (NT) are a subset of All Types (AT).

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