WLTP.

The acronym WLTP is short for "worldwide harmonized light-duty vehicle test procedure" and it represents a test method to determine vehicles' consumption and emission values on a roller test stand. The WLTP is being gradually introduced since 1 September 2017 and it replaces the previous NEDC test method. Thanks to its dynamic configuration, the WLTP is significantly closer to actual driving characteristics than the previously used method.

The WLTP is characterised by significantly higher accelerations and a much more dynamic driving profile. The top speed is raised to 131 km/h and the average speed increases to 47 km/h.

The driving time is extended by 10 minutes, the proportion of motorway journeys replicated on the roller test stand increases and times when the vehicle is at standstill are simultaneously cut. The distance driven is extended to 23 kilometres. Gearshift times are calculated in advance, specifically for each vehicle and drivetrain.

In future, all optional extras influencing vehicle aerodynamics, rolling resistance or vehicle mass will be taken into account in the assessment. The power consumption of convenience functions will also lead to increased CO2 values. The air conditioning is the only exception in the first stage of the WLTP.

The aim of the WLTP is to introduce a globally binding standard. In this context, EU countries are at the forefront. This helps when comparing the fuel consumption and the pollutant emissions of vehicles from different manufacturers. The standards also contribute to the fact that authorities can verify compliance with legal emission limit values – from hydrocarbon (HC) to carbon monoxide (CO), nitrogen oxides (NOx) and particulates.

The WLTP driving cycles are called WLTC – worldwide harmonized light-duty vehicles test cycles. Three different driving cycles have been developed for different vehicle types as part of the WLTP to take into account the corresponding power/weight ratio. The majority of passenger cars registered within the EU, with a power/weight ratio in excess of 34 kW/t (46 hp/t), are assigned to the WLTC category 3.

The test cycles for category 3 vehicles are made up of four parts – low, medium, high, extra high. They simulate vehicle operation in urban and extra-urban environments as well as dual carriageways and motorways.

NEDC (new European driving cycle) is the currently valid test cycle for passenger cars. The first European test cycle came into force in 1970 with the objective of providing values that were comparable and reproducible across all manufacturers. In 1992 it was extended beyond urban traffic situations.

At 34 km/h, the average speed of the NEDC is low, as are the acceleration specifications and the top speed of 120 km/h. The composition of the cycle no longer corresponds to the current average distribution of different journey sections.

Consequently the energy consumption of optional equipment and convenience functions, such as the air conditioning system, radio or seat heating are not included in the measurement. This is paired with technological parameters that benefit deviations. For instance, start/stop technology has a relatively high influence in NEDC as NEDC features a high proportion of times where the vehicle is not moving.

In the case of vehicles with manual transmissions no vehicle-specific parameters are taken into account when determining the shift timing points. This can result in large differences in consumption compared with actual operation. As a result of the continuous, technical progress NEDC is no longer adequate and outdated.

RDE is short for real driving emissions and represents an on-road test to verify pollutant emissions. It describes vehicles' on-road emission response in real conditions. Exhaust gas measurement for the purposes of model series authorisations used to be performed at test stations only. Since March 2016 it has also been necessary to measure emissions in real driving operation within a defined framework.

A PEMS unit (portable emissions measurement system) is used to determine nitrogen oxide (NOx) and carbon monoxide emissions (CO). At a later point particulate emissions will also be determined. In this process, there is no defined cycle and test drives as well as measurements are carried out in real, everyday traffic situations in compliance with the highway code. Vehicles are driven on public roads for between 90 and 120 minutes, one third each in urban environments, extra-urban environments and on motorways.

In urban environments the intended average speed is between 15 and 30 km/h, on motorways between 90 and a minimum of 110, but no faster than 145 km/h. The ambient temperature must be between 0 and 30° and the air conditioning system must be on. Test drives must not be carried out at altitudes above 700 metres above sea level and they must merely feature a maximum of 100 metres difference in altitude.

From September 2017 Euro 6 emission limit values must be complied with during RDE cycles. In the first step this applies to models to be newly certified from 1 September 2017 and from 1 September 2019 at the latest for all models.

Requesting RDE results

RDE results of Mercedes-Benz vehicles, determined by Mercedes-Benz as the manufacturer as well as by independent, officially certified, technical service providers, can be requested using a contact form stating the PEMS test range of the corresponding Mercedes-Benz vehicle.

The PEMS test range number associated with the vehicle is available from the homepage of the European Automobile Manufacturers Association (ACEA).

In contrast to NEDC, the WLTP driving cycle is ten minutes longer and features a mere 13 percent of time where the vehicle is not moving. The entire cycle covers 23.5 kilometres – more than double the NEDC with 11 kilometres. It features higher average speeds of up to 131 km/h, exposes vehicles to higher fluctuations in speed and is subject to significantly more stringent test specifications.

Additionally, not merely the basic variant of a model is tested as was the case up to now, but additional equipment and optional extras are also taken into account. Gearshift times are calculated in advance, specifically for each vehicle and drivetrain. Manual shifters benefit from this individual calculation compared with the firmly prescribed shift points under NEDC.

The introduction of the WLTP (worldwide harmonized light vehicle test procedure) creates more transparency in terms of fuel consumption. Customers benefit from the WLTP because they receive a more realistic, comparative benchmark for consumption and emission figures of different vehicle models.

However, CO2 and consumption values will also change as a result of different framework conditions: as a result of the process, a technically identical vehicle will produce numerically higher CO2 and consumption values than as part of NEDC (new European driving cycle). This comes as a result of factors including the inclusion of optional extras and more stringent framework conditions as part of the new cycle.

In future, customers will be able to determine the CO2 values of their vehicle model much more accurately as a result of the choice of optional extras. Mercedes-Benz will actively accompany the WLTP introduction phases and provide dealerships and customers with targeted information to guarantee clear-cut circumstances and a maximum degree of transparency.

The data will also include a new type of equipment-specific indication: from the model with the lowest energy requirement to the version with the highest energy requirement. Numerically, this spread stretches from "WLTP low" (minimum optional extras) to "WLTP high" (maximum optional extras).

Learn more by downloading our information brochure on diesel engines, emissions and the mobility of the future.