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WLTP emissions tests are designed to promise more reliable emissions figures, but not everyone is yet convinced

Problem solved. The new WLTP tests for economy and emissions are sweeping away the old and hopelessly outdated NEDC tests.

We now have economy figures that more closely match those achieved in the real world, and will switch to more accurate WLTP carbon dioxide emissions figures in April 2020.

But is it really that simple? There’s little doubt that the WLTP system is a huge improvement on NEDC, but there’s also evidence that the new regime has its foibles, too.

Emissions Analytics believes independent tests are vital

Emissions Analytics believes independent tests are vital

Nick Molden, CEO of Emissions Analytics, says his company has continued to carry out its own independent tests on the economy and CO2 output of vehicles. While the company’s results for diesel vehicles are broadly in line with the official figures, it has found a surprising discrepancy between its own results and the official figures for petrol models.

“While our real-world results for diesel cars are in line with WLTP data, indicating that manufacturers have got their house in order over diesel, the same cannot be said for petrol,” says Molden. Petrols achieved an average of 185g/km in Emissions Analytics tests, while the same cars emitted an average of 151g/km in WLTP testing, a discrepancy of more than a fifth.

Molden believes it likely that manufacturers are working to ‘optimise’ cars for the new test cycle.

Paul Mauerhoff, senior press manager, SMMT

Paul Mauerhoff, senior press manager, SMMT

It’s a suggestion the Society of Motor Manufacturers and Traders rebuffs. “We strongly reject these misleading claims, which at best betray a fundamental lack of understanding of the testing and regulatory process and at worst look like an attempt to unfairly discredit the automotive sector for commercial gain,” says Paul Mauerhoff, SMMT’s media manager. “The WLTP testing regime is the toughest in the world, more rigorous and complex than its predecessor NEDC and covering a wider range of driving behaviours to give fuel economy and emissions figures that better reflect on-road performance.”

However, Molden isn’t the only one suggesting that cars could potentially be prepared to meet the test standard. The clean transport campaign group, Transport and Environment, commissioned its own research earlier this year, testing three vehicles to the old NEDC standard and the new WLTP protocol. It found an average difference between the official WLTP figures and its own WLTP tests of 12%.

Florent Grelier, clean vehicles engineer, Transport & Environment

Florent Grelier, clean vehicles engineer, Transport & Environment

Florent Grelier, clean vehicles engineer at Transport and Environment, says: “The independent tests we commissioned show that the new CO2 emissions test will not prevent future test cheating. This means consumers will continue to spend more on fuel than they were told, and governments will miss their transport CO2 targets. To close this gap, we need real-world checks, including by independent third parties and the European Commission, and for this information to be available to drivers via accurate labelling.”

There is a mechanism built into the official tests that is supposed to make it more difficult for cars to be finessed to work well under lab conditions, but emit significantly more in regular driving. The Real Driving Emissions (RDE) test supplements lab-based WLTP tests with an on-road procedure. While RDE doesn’t test for CO2, it does check levels of particle number (PN) and nitrogen oxide (NOx) emissions, which are harmful to air quality.

Initially, RDE tests have allowed a ‘comformity factor’ of 2.1, meaning emissions 2.1 times greater than the lab standard were acceptable. The second phase of RDE, known as RDE2, requires cars to have NOx emissions within 1.5 times the lab standard (strictly speaking emissions should reach the same standard, but a ‘measuring tolerance’ of 0.5 still leaves some leeway).

Given that RDE2 is compulsory for new-to-market models from this coming January, and all new cars from January 2021, the SMMT believes fleet managers and business drivers can be confident that new cars really will be as clean across all circumstances.

“The WLTP regime is the toughest in the world, and covers a wider range of driving behaviours”

“RDE2 includes a wider range of performance conditions, including even greater altitude and much more extreme temperatures rarely encountered in the UK,” says the SMMT’s Mauerhoff. “This means buyers can be sure that the vehicle’s impact on air quality on the road is at least as low as that achieved in the WLTP lab test – and in many cases it will be lower.”

But as RDE2 doesn’t test CO2, does this show a need for independent on-road testing to be sure fleets and drivers know they can rely on the official figures?

“On-road testing of CO2 emissions can only ever provide a snapshot of how a vehicle is being driven and cannot be used as a comparison with official test values,” argues Mauerhoff.

Nick Molden, CEO, Emissions Analytics

Nick Molden, CEO, Emissions Analytics

Unsurprisingly, Molden disagrees. “The big thing with the old NEDC cycle, and that’s also a problem with WLTP, is that it’s deterministic: you can set up your vehicle to do well on that cycle. To do the same for on-road testing, manufacturers would have to optimise their cars over a much, much wider window, which defeats the point of optimisation. You rapidly come to the conclusion that you need to make sure a car is below the limit in all reasonable driving circumstances. That is the most important thing,” he says.

“Independent on-road testing means manufacturers don’t have a monopoly on the data, and the manufacturers can be scrutinised much more effectively.”

It may not be a popular message within the industry, but such independent testing could, in the future, form part of the solution to accurate official efficiency stats.

David Motton