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Everything you need to know about the new emissions rules

WLTP will change the fuel economy and emissions ratings of every new car on sale. So what is it and what does it mean for you?

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WLTP may not be the snappiest of abbreviations, but it will soon become an important part of the car-buying process along with monthly payment budgeting, creature comfort choices and, of course, colour.

In essence, this is a new fuel economy and emissions testing regime aimed at holding car manufacturers more accountable for the data they produce on new cars, while giving customers a more accurate picture of how their car will perform in the real world.

The Car Expert looks at what WLTP is all about and how it will become part of your decision making when buying a car.

A new Mercedes-Benz undergoing WLTP testing
Real-world emissions testing will now be done on all new cars.

What is WLTP?

WLTP stands for the somewhat cumbersome “World Harmonised Light Vehicle Test Procedure”.

It’s a new EU testing regime launched in September 2017. New cars are tested in a completely new way to give buyers more reliable figures on achievable miles per gallon (mpg) and carbon dioxide (CO2) emissions.

In theory, this should help you more accurately compare and select the car best suited to the type of driving you do. It will also determine how much road tax (actually called vehicle excise duty, or VED) or company car benefit-in-kind (BIK) tax you will have to pay; both of which will continue to be linked to CO2 emissions.

It’s now six months since WLTP was introduced, and in another six months (September 2018) there will be WLTP test information on all new cars on sale in UK showrooms.

Will Brexit affect whether these EU rules will apply to the UK?

No. Regardless of what happens with Brexit, this is a European-wide standard that is part of a wider regulatory process. It forces all car manufacturers to dramatically reduce the CO2 emissions of new cars.

Car makers have been ordered by the EU to reduce the average CO2 emissions across all new cars sold in 2021 to just 95g/km or face hefty fines. As all car manufacturers will have to build cars that comply with this order for other European markets anyway, it would make no sense for the UK to implement different regulations.

Why is WLTP being introduced?

Good question. The answers range from a genuine need to address air quality across the continent, especially in heavily congested cities – some of which have already moved to ban diesel-engined cars – as well as the lasting legacy of Dieselgate, where the Volkswagen Group was found to have falsified the CO2 ratings of certain vehicles when undergoing emission testing.

Volkswagen dieselgate headlines
No, Volkswagen, we haven’t forgotten.

Also, the previous system was antiquated and widely discredited. First introduced in the 1980s and not updated since 1997, the New European Driving Cycle (NEDC) relied solely on rolling-road tests to produce emissions and fuel economy ratings reflecting the best possible outcomes in controlled laboratory conditions.

However, cars have moved on since the NEDC tests were last updated more than 20 years ago. The average vehicle is now loaded with high-tech safety and comfort features, from electronic stability control, parking sensors and airbags, to air conditioning, heated windscreens and electric seats. Yet the way vehicles were tested had not kept pace, resulting in a gap between performance in the lab and on-road where fitment of these in-car technologies can differ across models, and conditions such as speed, congestion, road surface and driving style can vary dramatically from journey to journey and driver to driver.

These advanced safety and comfort features may not be fitted to vehicles as standard and only available at extra cost, or they may be fitted in some countries but not others. Many of these items can impact the weight and/or aerodynamics of a car, and therefore affect their emissions and fuel economy. Yet under the current rules, only the most basic model without any such extras is tested.

Under WLTP, cars will be individually rated according to what gear they have onboard. It’s fair to assume that the more kit is added, the poorer the rating will be, and this will impact pricing. Expect car makers to look closely at how they can bundle creature comforts together and delete some options to achieve the best possible ratings and prices.

The car manufacturers have also become exceptionally good at gaming the current system, by optimising their vehicles to perform better in the lab tests – even if that means compromising real-world performance for their customers. The idea is that this should not be possible under the new tests.

Ultimately, car buyers should get a better idea of what the real fuel economy and emissions levels of a new car should be under WLTP than the old NEDC tests.

Mercedes-Benz WLTP lab test
New WLTP lab test will make cars work harder and more accurately replicate real driving conditions.

How does the WLTP test fuel economy and emissions?

The old NEDC system determined test values based on a theoretical driving profile; think of boffins in lab coats with clipboards gathered around a car on a rolling road.

However, the WLTP cycle was developed using far more rigorous rolling road testing (see the infographic below), combined with real-world driving data to better represent everyday driving. What this means is that the boffins are still there (although clipboards have been traded for tablets) but their laboratory findings are married to those produced by cars driven by real drivers on real roads equipped with high-tech emissions measuring devices.

The WLTP driving cycle is divided into four parts with different average speeds reflecting different roads: low (city), medium (urban), high (A-road) and extra high (motorway). Each part contains a variety of driving phases, stops, acceleration and braking phases. For a certain car type, each powertrain configuration is tested with WLTP ratings reflecting the car’s lightest (most economical) and heaviest (least economical) loads.

WLTP was developed with the aim of being used as a global test cycle across different world regions, so tailpipe emissions and fuel consumption values would be comparable across borders. It will be the new standard across Europe, with other governments invited to recognise it for their countries.

What’s so real about real-world testing?

What differentiates WLTP from NEDC is the inclusion of (sorry folks!) yet another acronym: RDE, or Real Driving Emissions.

In a world first, new models being developed for sale in the UK and Europe will need to prove their air quality credentials by undergoing real-world road testing.

This uses special portable emissions measurement equipment to record and analyse the trace tailpipe emissions of pollutants CO2, nitrogen oxide (NOx) and particulates, while the car is driven in a wide range of every-day and extreme conditions, including carrying a heavy load up a steep hill at high speed in very low temperatures.

RDE testing has been designed to demonstrate that new cars’ emission ratings are those achieved in real-world conditions meaning the tough Euro-6 engine emissions standard are met on the road as well as in the lab.

Mahle portable emissions testing equipment
Portable emissions testing equipment

How do the NEDC test ratings compare with WLTP?

Not very well! It is expected that most cars tested under WLTP and RDE are likely to show poorer fuel economy and higher CO2 emissions than the same car tested under the old NEDC test.

According to JATO Dynamics, the automotive industry research company, cars already retested under WLTP are showing a greater than expected increase over their original NEDC CO2 rating.

Significant rises in CO2 emissions were found across the board. For example, a Peugeot 308 with a 1.2-litre 130hp petrol engine saw its rating rise from 104g/km (NEDC) to 117g/km (WLTP), an increase of 13%.

Meanwhile, a BMW X6 3.0-litre diesel increased from 157g/km (NEDC) to 183g/km (WLTP), an increase of 17%.

Expect similar discrepancies in the fuel consumption figures published by car manufacturers, especially as the current claimed combined ratings are mostly unachievable in real-world driving.

Will WLTP ratings apply to all new cars?

Yes. From September 2018, if a car has not got its WLTP certification it cannot be sold in the UK.

By September 2019, all cars will also have undergone the full RDE testing for both NOx and particulate emissions.

Is this the end of the old NEDC ratings?

Not just yet, as there will be a transition period in place while the new standards are phased in. New cars will be tested under both the new WLTP and old NEDC protocols until 2020. The exisiting NEDC ratings for CO2 and fuel consumption will still be used to calculate both road tax (VED) and benefit-in-kind (BIK) company car tax until 2020.

This will probably be confusing at first, but it will at least allow car buyers to see how inaccurate the old tests are in comparison to the new ones. If you are comparing different models when you are looking to buy a new car, it will be very important to make sure you are comparing like-for-like figures, rather than the new WLTP figure for one car against the old NEDC figure for another car.

Hopefully from 2020, when the old NEDC ratings are finally phased out, there will be more clarity.

WLTP vs NEDC emissions testing
Image (c) SMMT

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Curtis Hutchinson
Curtis Hutchinson
Curtis Hutchinson is a member of the Guild of Motoring Writers and has been a senior motoring journalist for over 25 years. He has written extensively about the automotive industry as editor of both Company Car and Motor Trader where he won the coveted Newspress Business Publication of the Year Award. His work also appears in Fleet World and Fleet World International. In 2016 he was part of the founding team behind the relaunched London Motor Show.