Environment and Climate

Exhaust emissions

Since the start of the nineties, the introduction of the standard European exhaust emissions regulations has meant that vehicle emissions in the EU are measured on the basis of a standard driving cycle.

Current legal framework: NEDC (New European Driving Cycle)

Legal limit values for measuring pollutants are specified across Europe. The first uniform emissions standards for passenger cars in the European Community took effect in 1970. The common label “Euro-norm” was introduced in 1992 with emissions level Euro 1. The currently applicable standard is Euro 6. Over the course of progression from Euro 1 to Euro 6, lawmakers lowered the passenger-car limits for nitrogen oxides by 97 percent and for particles by 98 percent. The EU standard values for fuel consumption and emissions are determined using a legally mandated method, the New European Driving Cycle (NEDC), on a test bench. Neither the test vehicle nor the measurement procedures may be modified. This is because the boundary conditions are clearly defined: for example, the car’s daytime running lights must be on, a specific engine oil must be used, and there are clear specifications for the type and size of the tires.

Difference between lab and street

As the NEDC was introduced back in 1996, it is now obsolete. The city driving proportion is too high and accelerations are too low. It also does not take into account varying landscape topography and faster expressway driving. The maximum speed of 120 km/h is driven for only ten seconds. The average speed of the NEDC is unrealistically low at 34 km/h. Features that are now taken for granted, such as air-conditioning, radio and seat heaters, are not covered, as they depend greatly on different user profiles. The goal of this legal requirement was essentially to provide a basis for comparison between various vehicle manufacturers. It soon became clear, however, that there is a difference between the test bench results and the values on the roads. There are many reasons for this.

Usage behavior, above all, has a substantial effect on fuel consumption and emissions: drivers who travel in the mountains a lot, drive faster on the expressway more often or use a lot of comfort functions that consume more fuel than others. There is not just one vehicle consumption level on the roads. The different load and dynamic requirements and selection of exhaust gas treatment systems play a critical role in exhaust emissions as well.

In addition, many technologies developed in recent years to reduce CO2 have a greater effect on the test bench than on the roads. Start-stop technology, now in widespread use, is one example of this. In the NEDC, it reduces fuel consumption by about 10 percent. In reality, this consumption advantage exists only in heavy traffic with a lot of stop-and-go driving.

Because vehicles are becoming more and more efficient, the value measured in the test cycle is also dropping. If the additional consumption due to features such as air-conditioning and the navigation system remain constant, then the percentage deviation that they cause will rise, although the absolute level of consumption is lower.

WLTP will replace NEFZ

Not only consumers, but also the manufacturers themselves have an interest in obtaining realistic consumption numbers with a new test cycle. Representatives of the UNECE (United Nations Economic Commission for Europe) have therefore developed a new procedure with the support of the automotive industry, including the VDA. In 2017, the obsolete NEDC is to be replaced by the modern standard WLTP (Worldwide Harmonized Light Vehicles Test Procedures). With higher average speeds of up to 131 km/h, greater variations in speed and more strict test procedures, it provides a better overall picture of fuel consumption under real driving conditions. Like the NEDC, the WLTP cycle is also measured on a test bench. It specifies standardized, reproducible and comparable test conditions for national and international vehicle manufacturers. It provides customers with a better measuring stick for the consumption and emissions values of different car models. It provides manufacturers with a legally reliable basis for certifying new vehicles.

The VDA supports the introduction of this new measurement method, as it gives automobile manufacturers the ability to communicate more realistic consumption values. Nevertheless, the WLTP standard will also not reflect fuel consumption on the roads or real emissions in all cases, because consumption and emissions are also dependent on driving style and environmental conditions.

Conversion from NEDC to WLTP affects not only consumption measurements, but also CO2 fleet monitoring and the challenging CO2 laws in Europe. The 95 g fleet target value was established on the basis of the NEDC. If the measurement method for determining CO2 emissions is to be changed, then the target value must also be adjusted accordingly. On average, the automotive industry expects a nominal increase in fuel consumption values of about 15–20 percent when using the WLTP to determine fuel consumption. A method has been developed for introducing the WLTP into CO2 legislation, which provides for converting WLTP measurements back to NEDC values at first. The intent of the EU Commission is that this will ensure that the launch of the WLTP does not bring about an intensification of CO2 legislation.

New WLTP cycle

  WLTP NEDC (New European Driving Cycle)
Starting temperature Cold Cold
Cycle time 30 min. 20 min.
Idle time element 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
Propulsive power Average: 7.5 kW – Maximum: 47 kW Average: 4 kW – Maximum: 34 kW
Influence of special equipment and
Special equipment is considered for weight,
aerodynamics and onboard electrical
system (quiescent current). No AC
Currently not considered

Real Driving Emissions

Exhaust gas measurements will also be converted to the WLTP in the future. Pollutant limits, however, will not be affected. WLTP laboratory measurements will in future be supplemented by the so-called RDE test (Real Driving Emissions), which will measure vehicle pollutant emissions directly on the road for the first time. The regulation was adopted in its final form by the European Parliament at the beginning of 2016. The VDA advocated for and welcomes the road measurements. Unlike the laboratory investigation, the RDE test does not require compliance with any fixed driving cycle. In practice, the RDE test will be conducted under any environmental conditions. Acceleration, outside temperature, wind conditions and traffic situation are random. The intention behind this additional test in future is to reduce the differences between test stand and everyday car use. Manipulations, especially using software that detects the test bench situation, will thus no longer be possible. For the RDE test, vehicles will be equipped with so-called PEMS technology (Portable Emissions Measurement System) for mobile emissions measurement. PEMS is already used as standard for commercial vehicles.

Differences between test bench measurements and road tests are generally due to technical reasons and depend on individual usage as well as individual environmental boundary conditions. Extreme values in excess of limits, however, are inconsistent with the spirit of current emissions regulations. That is why the automotive industry is advocating the rapid introduction of the RDE legislation that has now passed, so as to avoid large discrepancies between laboratory and road values in future.

With RDE, vehicles have to comply with nitrogen oxide limits not only on the test bench, but also under real driving conditions and nearly any environmental conditions. The only concessions by lawmakers are consideration of the measurement tolerance of the portable emissions tester and a slightly higher limit for a transition period of 15 months after the introduction of RDE (conformity factor 2.1 including PEMS measurement tolerance) in order to allow the entire passenger car fleet to be converted to these new RDE limits. Compared with Euro 5, the final RDE regulation means a reduction in emissions by a factor of five.

The VDA expects that the air quality targets in Germany will be achieved by Euro 6 in conjunction with RDE. This is primarily the conclusion of a study by the Aachen research institute AVISO, in cooperation with Graz Technical University and the Heidelberg environmental institute ifeu. The result of the study is that the violation of air pollutant limits will be solved by the increasing market penetration of Euro 6 and RDE. Natural fleet replacement alone will reduce nitrogen oxide levels in the air by 17 percent by 2020. This means that measurement points that currently have an annual average of 48 μg/m³ will meet the limit of 40 μg/m³ in the future. This means that 33 of 72 measurement points that exceed the limit will be brought down to target levels.

Real Driving Emissions regulation (RDE) - Deadlines and conformity factor

  Conformity factor Date applicable  
Measurement tolerance of PEMS devices (currently 0.5) is already included in the factors New models: all models with type approval after the date indicated. All new registrations: all vehicles newly registered after the date indicated. Slightly used vehicles one year later in each case
New models All new registrations
1st step 2.1 September 2017 September 2019
2nd step 1.5 January 2020 January 2021
Dr. Jakob Seiler Consultant

Tel: +49-30-897842-285 Fax: +49-30-897842-606
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