WLTP and NEDC. Part II: Comparing the measurements

For around 25 years, the NEDC was the valid test cycle for vehicles in the EU. From September 1, 2017, it is being replaced, in two phases to the end of August 2018, by the new WLTP test cycle (Worldwide Harmonized Light Vehicles Test Procedure).

Outdated – but still relevant: the NEDC

This means that all vehicle models to be newly certified for emissions will now be tested under WLTP*. At the same time, however, an NEDC consumption value will continue to be calculated for these vehicles and will for the near future still be shown as the legally required figure in sales materials and all other publications.

*The terminology distinguishes WLTP, the procedure as a whole (which also includes the framework conditions of testing) and WLTC, the driving cycle in the narrower sense. For the sake of simplicity, we will dispense with this distinction in the further course.

In addition, the so-called CO₂ fleet compliance, the average value of each manufacturer's fleet, which serves to meet the climate targets, will still be shown in the NEDC up to and including 2020. In this transition phase, therefore, "NEDC values" will continue to be calculated from the WLTP measurement. This is done using the so-called "CO₂MPAS tool", which is made available by the legal authorities for converting WLTP values to NEDC values. Despite all the changes, the basic principles of the test, according to type of powertrain, remain unchanged. Here are the main features of the measurement at a glance:

Dynamometer measurement

Vehicles with internal combustion engine Plug-in hybrid vehicles Electric vehicles
A dynamometer cycle, defined by duration, route profile (city, country, freeway), temperature conditions, acceleration, etc., is run once. The cycle is repeated, similarly to vehicles with a combustion engine, until the battery of the hybrid vehicle is fully discharged. This measures the all-electric range. The cycle is repeated, similarly to a plug-in hybrid, until the battery is fully discharged.
As the result, the fuel consumption is calculated from the CO₂ emissions. The pollutant emissions (NOx, particulates, …) are also measured. The electric range as a ratio of the total range yields the utility factor (UF). The PiH utility factor is between 100% (all-electric vehicle) and 0% (combustion engine only). A charger equipped with an electricity meter is used to measure the power consumption in kWh until the battery is fully charged.
  The CO₂ value is calculated from the conventional driving share and the measured CO₂ emissions. The electricity consumed and the range of the vehicle yield the electricity demand in kWh/100 km.

WLTP - new cycle for the dynamometer

The WLTP cycle (Worldwide Harmonized Light Vehicle Test Procedure) is, therefore, now the measure of all things. Originally, it was intended as a worldwide, harmonized test procedure. For this reason, sample driving profiles "from all over the world" actually went into creating the cycle. Ultimately, however, the goal of worldwide harmonization could not be achieved, because the USA and China pulled out of the talks over the way consumption is measured, while other countries objected to the design of the "WLTP".

At present, the WLTP applies in the EU and is likely to be adopted in further countries such as Japan, India and Australia. Despite that, there are specific additions for every country – for example, Japan is dropping the freeway cycle, which is of no relevance for day-to-day driving in that country. As with the previous NEDC, the measurement takes place on a dynamometer and requires standardized, reproducible and comparable test conditions for all vehicle manufacturers. So is this old wine in new bottles? Not quite: The new cycle delivers test results that are more closely based on real driving conditions and therefore provides greater transparency. It also remains clear, however, that a standardized test cycle is not able to reflect the specific consumption of each individual and that there will continue to be deviations.

What can the new cycle do?

Measurement procedures, too, must move with the times. Vehicles and user behavior have undergone substantial changes in the past 20 years. Our vehicles, for example, have more powerful engines and more optional equipment, which affects the consumption; also, daily driving distances have become longer on average, while journey times have increased due to traffic congestion. The WLTP is intended to take all of these factors more accurately into account. The main changes:

Parameter WLTP NEDC
Starting temperature cold cold
Cycle time 1,800 s 1,180 s
Endurance 242 s 267 s
Stop share 13.4 % 22.6 %
Distance 23,262 10,931
Maximum speed 131.3 km/h 120 km/h
Average velocity 46.5 km/h 33.35 km/h
Temperature 23 °C 25+/-5 °C
Special equipment of the individual model are considered for weight, aerodynamics, rolling resistance, on-board power requirements; without air conditioning during phase I. out of tyres are disregarded; without air conditioning

The advantages:

• The WLTP provides customers with a more realistic yardstick for comparing the consumption and emissions of different vehicle models.

• Also for us as a manufacturer, it provides a legally reliable basis for the certification of new vehicles.

• In addition to consumption and emissions measurements on the dynamometer, it will be necessary in future also to meet the emissions limits on the road, as required by the new Euro 6d TEMP standard. This led to the development of the RDE (Real Driving Emissions) test, which likewise was introduced on September 1, 2017. This involves the use of a PEMS (Portable Emissions Measuring System) to measure the emissions of vehicles in real road traffic. Since September 2017, the RDE measurement – and therefore the obligation "Not to Exceed Limits" also on the road – has been a necessary requirement for the granting of type approvals by the KBA (German Federal Motor Transport Authority).

All of this will result in a significantly more realistic representation of the emissions and consumption of new model series. According to the German Association of the Automotive Industry (VDA), however, it is to be expected that, on average across the EU (weighted by unit sales), the switch from NEDC to WLTP – also described as a "currency reform" – will mean a numerical increase of the CO2 values by 22 percent in comparison with NEDC-certified vehicles. Especially in communications with customers, this has the drawback of one and the same vehicle having apparently worse figures, although there has been no change in technology. Necessary information is provided by, for example, the new WLTP website of Mercedes-Benz.

We use cookies

We want to make our website more user-friendly and continuously improve it. If you continue to use the website, you agree to the use of cookies.