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Real-world vehicle emissions

Road vehicles are a major source of air pollutant emissions. This involves substances such as nitrogen oxides (NOx) and particulate matter (including PM10), both of which are harmful to health. Vehicle emissions must be reduced to meet European requirements for local air quality and for emissions at national level. In addition, road vehicles that run on fossil fuels emit carbon dioxide (CO2). CO2 is a greenhouse gas that contributes to global warming. European legislation is setting increasingly stringent requirements on road vehicle emissions.

The Dutch government is committed to making vehicles cleaner and more fuel-efficient. To do this, and to do this as soon as possible, the Netherlands is bringing additional instruments to bear, such as tax incentives, temporary subsidies, and environmental zones. Also, there is active Dutch involvement in Brussels, aiming to achieve effective European legislation that brings down the real-world vehicle emissions.

Objective information for supporting and monitoring policies

In designing effective emission legislation, the government has to be able to rely on objective data on emissions and other car performance parameters. TNO has, therefore, been commissioned by the Ministry of Infrastructure and the Environment to measure the real-world emission performance of road vehicles. Measurements are made on a dynamometer in the lab and when driving on the road using mobile emission measuring equipment. There are two separate measurement programmes: one for passenger cars and vans and one for trucks and buses.
The aim of TNO’s measurements is twofold. Based on an average picture of real-world emissions, national road vehicle emission factors are established each year. These emission factors are used to calculate air quality, to determine total emissions, and to calculate the effectiveness of policy measures. Emission factors are always based on measurements of real-world emissions, not on the emissions reported in type-approval testing.

TNO brings its knowledge of vehicle emissions to bear in the context of several national and international working groups that are involved in determining emission factors. In the Netherlands, that would be the Task Force on Traffic and Transportation, while at international level it is ERMES (European Research for Mobile Emission Sources) and EURISEC (European In-Service Emission Conformity).

In addition, TNO’s results are an important basis for input from the Ministry of Infrastructure and the Environment and the Netherlands Vehicle Authority in the development of new European emission standards and related testing procedures. Accordingly, TNO has been working with these parties in Brussels for several years, to develop legislation for real-world emissions, also known as Real Driving Emissions or RDE. This new legislation should ensure that vehicles are clean, not only on the dynamometer, but when they are out on the road as well. Legislation of this kind has already been introduced for trucks, and the beneficial results are clearly visible.

TNO has no enforcement function. The measurement results are published, and are always discussed extensively and in depth with the Ministry of Infrastructure and the Environment, the car importers concerned, manufacturers, and other stakeholders such as the RAI Association and BOVAG (the Association of Car Dealers and Garage Holders).

Diesel vehicles: marked reduction in particulate matter emissions, but the NOx emissions of diesel cars and vans continues to be a point of concern

With regard to air pollutant emissions, petrol vehicles are now fitted with catalytic converters, so they have been relatively clean for quite some time. Modern cars, vans, trucks and buses that run on diesel are all equipped with closed diesel particulate filters. These provide a very significant reduction in particulate emissions from diesel vehicles.

In the case of trucks and buses, the introduction of more stringent standards, together with the addition of a real-world test to the type-approval testing procedure, has also led to substantial reductions in real-world emissions of NOx. On average, in everyday use, modern heavy Euro VI trucks emit just one tenth of the NOx emitted by previous generations of trucks (Euro IV and V).

For some years, however, TNO has identified major and growing differences between the NOx emissions of diesel cars and vans measured during type-approval testing, and the corresponding emissions under real-world conditions. European emission limits are becoming increasingly stringent. Since 2010, these vehicles have been subject to NOx reduction measures such as exhaust gas recirculation (EGR) and selective catalytic reduction (SCR). Despite this, however, the real-world emissions of NOx by diesel cars and vans over the past two decades have remained virtually unchanged. As a result, the real-world emissions of modern cars and vans are substantially higher than the limits set for type-approval testing in emissions legislation.

TNO’s contribution

TNO is helping to reduce road vehicle emissions in a variety of ways. As an independent institute, TNO is working to generate reliable insights into real-world emissions. TNO supports government bodies, businesses and other stakeholders in their efforts to achieve effective reductions in such emissions.

On the one hand, this involves carrying out measurement programmes, developing new measurement methods, testing new technologies, and providing objective, fact-based advice to all of the parties concerned. This work involves advising local authorities on the design of effective policies to meet current European air quality standards and on how to achieve more far-reaching targets for clean and healthy air.

In addition, TNO is developing various technical and non-technical solutions to help reduce the environmental impact of road vehicles in real-world situations.

Read more

You can find the most recent reports on emission measurements for road vehicles on the pages below and by clicking on the news item at the bottom of this page.

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