EU urges use of roadside sensors on car emissions

"Remote sensing is a powerful tool," said Dilara.

The concept is somewhat similar to using radar speed guns to determine if someone is driving too fast. Dilara said it was a way for authorities to identify car models that have suspiciously high emissions.

In the past two years it has emerged that the use of so-called defeat devices, which make a car appear cleaner during the official test than it actually was, was widespread in Europe.

The currently most often used method to spot dirty cars on-road is the portable emissions measurement equipment, or Pems, which is mounted on a single car to measure actual emissions.

Until the beginning of this month, all official tests were done only in a laboratory, but now cars coming on the road have to pass a Real Driving Emissions (RDE) test.

"We have to move on from the very dumb form of testing that we have at the moment, where we put a specially prepared vehicle into a laboratory," said clean transport campaigner Greg Archer, from the environmentalist organisation Transport & Environment.

"We run it for half an hour, we measure with enormous accuracy and massive reproducibility what the emissions are, and it bears no resemblance at all to how that car performs on the road. That's at the heart of our current scandal," he said.

Archer said the RDE test was "a massive step forward", and that remote sensing "is a really strong and complementary tool", that could be used in combination with Pems.

Deterrent

"It is clear that in most cases [of remote sensing] we need to do further testing to know what exactly went wrong for this vehicle," said Dilara.

"We think that together with our RDE legislation, if we apply things like remote sensing, it will be an appropriate deterrent to prevent both tampering and defeat devices," she added.

While defeat devices are typically put in cars by carmakers, for instance to cut costs, tampering with emissions filter technology is sometimes done by individual car owners, to boost performance or to save on fuel.

After the Dieselgate scandal, the EU parliament called on member states to "establish remote fleet monitoring schemes" by using roadside remote sensing equipment and/or on-board sensors.

Remote sensing is more prevalent in the United States, and several Americans attended Thursday's event in the parliament searching for business opportunities.

Only part of the puzzle

Vicente Franco, another policy officer at the EU commission, also supported the use of the tool, but warned against seeing it as a silver bullet.

Franco said the analogy with the radar speed gun only worked to an extent.

"If you register 70 kilometres per hour and the speed limit is 55, you can be pretty sure that that car was not in compliance and that you can fine that car," said Franco.

But the emissions of nitrogen oxides (NOx) are not as binary as going over the speed limit or not.

The NOx limits were measured in milligrams per kilometre, but they were sometimes clustered around "emission events" like acceleration, said Franco.

"If you happen to catch those events with remote sensing, it might look as if that car is very dirty, when actually it might just be a little bit unlucky," he said.

He said a "robust statistical analysis framework" was needed to be able to draw conclusions.

Additionally, even if remote sensing is deployed all across Europe, it is still up to national authorities to actually enforce the emissions legislation, something which, in the years before Dieselgate broke out, they neglected to do, and, even now, remain reluctant to do.