Taking to the road

Since September 2017, new cars have been required to prove how clean they are in actual road conditions. TÜV NORD has pioneered the mobile measurement technology known as PEMS, which the company anticipates will play a key role across Europe in the provision of more realistic exhaust gas measurements and, in consequence, help clean up road traffic.


Some drivers may be surprised in the future to see an unusual array of devices on a trailer behind the vehicle in front of them. What looks like a compact generator or a futuristic refrigerator is in fact a Portable Emission Measurement System, or PEMS. It measures the emissions of nitrogen oxides and particulates in car exhaust gas and represents a small revolution with profound consequences: car exhausts have to date been tested only under laboratory conditions on chassis dynamometers. The previous laboratory test, NEDC (New European Driving Cycle), guaranteed comparable measurement results but was increasingly criticised as inapplicable to real driving conditions. Even worse, it also turned out to be manipulable. “We had to concede that there are differences between measurements taken in the laboratory and on the road,” explains Helge Schmidt, technical director for Drive Systems / Car Emissions / Motorcycles at the Institute for Vehicle Technology and Mobility (IFM) of TÜV NORD. That there are differences between laboratory and road conditions is nothing new. And yet, the 2015 diesel scandal made the EU Commission starkly aware of the scale of these differences and prompted it to act.

Real road conditions from the computer

Is it possible to use Big Data procedures to predict how much exhaust gas a car tested in the laboratory will emit on the road? The exhaust emissions experts from TÜV NORD are exploring new ways of answering this question. In collaboration with IBM, they are feeding the artificial intelligence known as Watson with their data from laboratory and road tests. The results are encouraging. Such simulations will not replace genuine RDE tests conducted for approval. However, they might help auto manufacturers factor the real demands of road driving into the adaptation of the exhaust gas reduction systems in their vehicles in the development phase.

Improving exhaust gas reduction

A study has shown that nine out of ten Euro-6 diesel cars fail under road conditions to meet the targets for approval they have previously satisfied under NEDC conditions. On average, they emit 4.5 times more harmful nitrogen oxide than the permitted threshold. It is the increase in nitrogen oxide levels over those recorded using NEDC that is widely assumed to explain why urban nitrogen oxide levels are not falling as required by the law. “If we measure these pollutants on the road, we’ll be able to significantly reduce the negative impact of road traffic on the environment,” explains exhaust gas expert Mr Schmidt. If they want their vehicles to be approved for road use, the manufacturers will have to respond to more precise measurements with improved exhaust gas reduction technology. More realistic measuring procedures are thus becoming a key task for the future of clean road traffic, to which Mr Schmidt and his team can contribute.

Clean road traffic thanks to precise measurements

The response of policymakers to the difference between the laboratory and reality has been to impose more stringent measuring procedures. In September 2017, a regulation was enacted in the EU which the experts from TÜV NORD had been working toward in EU working groups and as consultants to state legislature: new cars presented for type approval must now undergo the Worldwide harmonised Light vehicles Test Procedure (WLTP), which more closely reflects real-life conditions and has superseded the NEDC.

Only every 10th modern diesel with exhaust gas standard 6 is as clean on the roads as it is during tests in the laboratory. 90 % exceed the tolerances for nitrogen oxides.

But even more realistic laboratory tests only approximate to reality and can in principle still be manipulated. Since September 2017, therefore, at European level emissions have also been tested on the road using the Real Driving Emissions procedure (RDE). Mr Schmidt and his team were among the pioneers of PEMS technology. In 2004, they deployed one of the first PEMS devices in Europe in a project for the German Federal institution for road (traffic and engineering) issues. Since then, they have been steadily working toward their objective: to advance the cause of clean traffic with more precise measuring procedures. In 2010, they measured real pollutant emissions from diesel vehicles in Stuttgart, a city plagued by particulate and nitrogen oxide emissions. Since 2012, by order of the Swedish government, the TÜV experts have been testing the exhaust emissions of vehicles already in use in road traffic. “Our experience from these projects was then factored into the development of equipment and the new regulations,” explains Helge Schmidt.

In the medium term, it will not be possible to dispense with chassis dynamometer tests, says Mr Schmidt. At the end of the day, influence factors such as ambient temperature can only be reproduced in laboratories. However, the RDE tests are designed to provide the greatest possible comparability. Also defined alongside the proportion of journeys made on country roads, motorways and in urban areas are, for example, minimum and maximum speeds and differences in altitude.

Series-production vehicles also to be tested

If exhaust gas emission expert Mr Schmidt has his way, series-production vehicles with a few thousand kilometres on the clock will also be routinely tested in future. After all, it will be of little use to people and the environment if exhaust gas reduction technology only half works in daily use. CO₂ emissions and fuel consumption, so important for both the climate and consumers, should in the future also be measured on the road. This is already technically possible. However, CO₂ emissions are extremely sensitive to the behaviour of individual drivers. “For this reason, it’s crucial to define the conditions for test drives and push ahead with the evaluation of the measurement results,” Mr Schmidt explains. A key task for the future of clean road traffic, in which he and his team have a crucial role to play.