Car exposed for poor motorway NOx emissions

European environmental organisation Green NCAP has discovered that the Skoda Octavia has 'poor' NOx emissions for motorway driving for the engine tested in its own, independent tests, despite this engine meeting the latest EU official emissions standard. Green NCAP tests go beyond the requirements of the official standard.

In Green NCAP's own 'high-load highway test', which aims to replicate driving conditions out on the motorway, the organisation said emissions were so high that the car failed to score any points in this part of its assessment.

The Skoda Octavia 2.0 TDi DSG 4×2 diesel automatic tested by Green NCAP achieved 'good' or 'adequate' ratings in most of its independent emission and fuel efficiency tests.

Green NCAP is a new consortium, partly funded by Which?, that provides independent environmental tests for cars. It goes beyond the minimum legal requirements to improve standards, similar to how Euro NCAP has improved car safety through its independent crash tests.

Find out the full results for cars recently tested by Green NCAP below, including the Seat Arona SUV, Vauxhall Corsa and Renault Scenic.

If cars produce hefty emissions in our own rigorous Which? tests, we won't recommend them. Find out the best cars to buy on the market right now.

How do Green NCAP tests work?

Green NCAP currently tests the environmental credentials of cars in two ways:

• Emissions tests, which aim to reflect real-life driving as much as possible and go further than the latest EU official emissions tests.
• Fuel efficiency, to ensure a car isn't using excessive amounts of fuel per distance travelled.

It's important to test cars in both ways, as it's possible to have a low-emission car that guzzles fuel, and vice versa. It's particularly challenging to design a combustion engine car that gets good results for both.

Green NCAP assigns each car (for the tested engines) a single rating out of five stars, just like how Euro NCAP assigns ratings for car safety.

Skoda Octavia, £17,158

The third-generation Skoda Octavia 2.0 TDi DSG 4×2 diesel automatic model's fuel efficiency was generally rated as 'adequate', although it dropped to 'marginal' for the motorway test. It was actually rated 'good' for most types of emissions, but NOx emissions really let it down.

For most tests, NOx was rated as 'adequate', but this fell to only 'marginal' when running the engine from a cold start. This flaw was fully exposed in the high-load motorway test, where NOx emissions were so high it scored zero points for this part of the test.

NOx emissions include NO2, which is toxic to humans and linked to rising concerns about air pollution.

Overall, the Skoda Octavia scored three stars out of five in Green NCAP's tests, with the 2.0 TDi DSG 4×2 diesel automatic model tested.

What did we think of the Skoda Octavia in our comprehensive tests? Find out how great it is to drive, how practical and reliable it is and more in our extensive Skoda Octavia review.

Seat Arona, £15,813

The Seat Arona SUV achieved a 'strong' four out of five stars in Green NCAP's latest tests, with the 1.5 TSI 4×2 petrol manual model tested.

In fact, it almost achieved full marks in its emissions tests, due to it having exhaust after-treatment tech on board, including a three-way catalyst and gasoline particulate filter.

Unfortunately, it performed worse in the energy efficiency tests, achieving mostly 'adequate' ratings and a 'marginal' rating for motorway driving.

So how is it to drive, what's its mpg like for urban driving, and is it a practical family car? Find out in our expertSeat Arona review.

Mercedes-Benz C-Class, £25,762

The current-generation Mercedes-Benz C-Class large car proves that the diesel stigma as a dirty fuel isn't always the case for the latest cars.

While the car achieved a disappointing three stars out of five overall in Green NCAP's latest tests, with the C220d 4Matic diesel automatic model tested, it achieved a perfect score in the emissions tests.

Green NCAP praised it as 'performing exceptionally well, with very low values of pollutant emissions in all tests'.

It's the first non-electric car to achieve maximum marks in Green NCAP's emissions tests. Its secret is its effective selective catalyst reduction and a diesel particulate filter for treating emissions before they enter the environment.

Unfortunately, the car's overall rating was brought down in the energy efficiency tests, where it was rated as 'adequate' in most tests and 'marginal' in the cold engine start and motorway tests.

Could its reliability and handling make it a great low-emission choice? We reveal all in our definitiveMercedes-Benz C-Class review.

Renault Scenic, £20,849

Renault's fourth-generation Scenic MPV achieved three stars out of five in Green NCAP's latest tests, with the Blue dCi 150 4×2 diesel manual model tested. It only missed out on four stars by a narrow margin.

Green NCAP found that the emissions were almost all 'good', but unfortunately there was a 'poor' result for NOx emissions in the organisation's motorway test. However, unlike the Skoda Octavia, it scored 4/9 in the highway test, so the result was still better than the Skoda Octavia's 0/9 rating for the same test.

The engine's fuel efficiency was generally rated as 'adequate', with a 'marginal' result in the high-load highway test.

Could this be the ideal low-emission car for your family? See what our experts thought in our definitiveRenault Scenic review.

Vauxhall Corsa, £11,735

The Vauxhall Corsa achieved a good four stars out of five in Green NCAP's latest tests. Green NCAP tested the fifth-generation Corsa E 1.0-litre petrol manual.

In the emissions tests, the Vauxhall car generally received 'good' or 'adequate' results. But particulate emissions were 'marginal' with a cold start to the engine, and carbon monoxide emissions 'weak' on the motorway.

Results were mostly 'adequate' for fuel efficiency, but fell to 'marginal' in the motorway test.

The Corsa is one of the UK's bestselling cars. Is it good to drive and how reliable is it? We reveal all in ourVauxhall Corsa review.

Nissan Leaf, £30,879

The second-generation Nissan Leaf mid-sized electric car achieved a full five out of five stars in Green NCAP's latest tests, with the 40 kWh N-CONNECTA electric automatic model tested.

Since electric cars don't have tailpipe emissions, they automatically get full marks in the emissions tests. The Nissan Leaf also achieved universally 'good' results in the energy efficiency tests.

Currently it can be argued that Green NCAP's tests favour electric vehicles, since they don't take into account the energy involved in producing the electricity on which electric cars run. In the future, Green NCAP hopes to move towards 'well-to-wheel' testing, which would take into account where the fuel comes from.

Are you looking for a great car with low tailpipe emissions? See how the Nissan Leaf performed in our thorough tests in our fullNissan Leaf review.