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What are WLTP and RDE?

To keep emissions down, all new cars now undergo rigorous tests called WLTP and RDE. Here’s what they both mean, and how they’ll impact your car tax, car performance and the environment.

All new cars now go through complex and rigorous lab tests called WLTP and RDE. These are new tests for a vehicle’s fuel economy and emissions, designed to give more accurate figures than their predecessors.
What does all this mean for you if you own a car, or are looking to buy your next car? And what do the new tests involve? Let’s lay it all out.

What is WLTP?

WLTP is an abbreviated acronym for “Worldwide Harmonised Light Vehicle Test Procedure”. This procedure is a series of laboratory tests designed to measure fuel consumption and emissions for passenger vehicles, as well as the range of electric vehicles.
WLTP was brought in for all new cars registered from 1 September 2018 and replaced the old NEDC tests, which didn’t accurately reflect real-world driving.
Car on a sunlit road
WLTP is closer to on-the-road performance

What does WLTP measure?

The WLTP test, which was developed by the European Union, aims to better represent everyday driving.
WLTP measures: • CO2 emissions • Pollutant emissions like nitrogen oxide (NOx) and particulates • Electric vehicle range • Energy consumption values of alternative powertrains (including hybrids and EVs) WLTP standards are based on real-driving data from around the world, and better match on-road performance. Because the test conditions are more realistic, the results are more accurate and truer to life. Unfortunately, that means a lot of the results appear worse than the NEDC figures for the same model, a situation confused further by some manufacturers sometimes publishing both in their brochures or using the ‘old’ figure to make their cars look more efficient. If in doubt always check the small print.

What are Euro 6 emissions standards?

Euro 6 emissions standards are the end goal of these tests.
If a manufacturer wants to sell a car in Europe, it has to meet the Euro 6 standards on the official WLTP (and RDE) tests. Euro 6 is the sixth iteration of the EU directive to reduce harmful pollutants (a directive is goal that all EU countries must legally strive to achieve). Euro 6 was introduced in September 2015, so all mass-produced cars sold from this date onwards need to meet these emissions standards before they can legally be sold. The UK adopted EU emissions regulations, including Euro 6, after Brexit so this will continue to apply here for the foreseeable.
Vehicles parked on dual lanes
Vehicles must meet Euro 6 standards to legally be on the road

What will WLTP affect?

So, what does this mean for you as a motorist? There are couple of key areas:

WLTP’s effect on car performance

WLTP doesn’t directly affect a car’s performance, but it has changed how that performance is reported.
Because WLTP is more rigorous, and more accurate when it comes to emissions and fuel economy data, than NEDC tests, vehicles now record a higher g/km CO2 value (which is the amount of CO2 emissions they produce). As such, manufacturers will have to change their vehicles to meet the Euro 6 standards. When WLTP was introduced, some manufacturers removed optional extras (like roof rails or a sunroof) as that would have tipped them over the limit. Essentially, the level of emissions being recorded went up. Vehicles were always emitting those levels; it just wasn’t being reported properly. Now it is and manufacturers are looking to fix it.

WLTP’s effect on car tax

As of April 2020, annual car tax in the UK is now calculated using WLTP standards.
UK car tax is calculated based on a vehicle’s level of emissions. Because WLTP tests are more demanding and accurate, vehicles are likely to record higher emissions and thus be liable for more tax. So yes, thanks to WLTP you’ll be paying more car tax for a more polluting vehicle. Tax rates are based on a vehicle’s CO2 emissions for the first 12 months on the road, after then it remains a flat annual fee. For petrol or diesel cars, this is £150 per year. For hybrids and alternative fuel cars like liquid petroleum gas (LPG), this will be £140 per year. Zero-emissions cars, like electric cars, won’t pay any car tax. Learn more about April 2020’s car tax changes.

WLTP’s effect on the environment

Manufacturers now have to meet WLTP and Euro 6 emissions standards, which are much better for the environment than previous standards.
For example, NOx emissions from diesel engines need to be 67% lower under Euro 6 standards than under the previous Euro 5 standards. To pass WLTP and meet Euro 6, manufacturers are making their vehicles much eco-friendlier and driving the level of emissions down. Vehicles will also have to meet Euro 6 emissions standards to enter low emission zones, such as London’s ULEZ, without paying charges. Learn more about low emission zones.
Lab tests performed on a car
WLTP tests are conducted in the lab

What do WLTP tests involve?

WLTP tests are done in a lab but are based on real driving scenarios, including longer test times over a greater distance, higher average speeds and more realistic test temperatures than old tests.
The tests are divided into four parts with different average speeds (low, medium, high and extra high speed), and each part of the test contains a variety of different driving phases, such as acceleration and braking. For each make and model, every version (including different engines, gearboxes and so on) is tested, from the lightest (most economical) to heaviest (least economical). This makes make it easier to compare different models and consider any options fitted that might affect aerodynamics or weight. WLTP tests include: • Wider range of driving situations, including urban and motorway driving • Stricter measurement conditions • More realistic driving behaviour: including accelerations, decelerations and braking • Higher average and maximum speeds and drive power • Longer test distances • More realistic temperatures • Shorter stops The results offer the best- and worst-case values for a more informed decision-making process.
Fumes and pollutants coming from an exhaust
RDE tests exhaust pollutants

What is RDE?

The Real Driving Emissions (RDE) test became compulsory for all new cars registered from 1 September 2019.
RDE tests measure tailpipe emissions and exhaust pollutants emitted by cars while driven on the road, and work alongside the WLTP lab tests by verifying the lab results with real world driving. The tailpipe emissions measured in real-world driving include nitrogen oxide (NOx) and particulates.

What do RDE tests involve?

During an RDE test, a Portable Emission Measuring System (PEMS) is fitted to a vehicle. This vehicle then goes out onto the open roads, covering a wide range of different conditions.
These driving conditions include low and high altitudes, year-round temperatures, additional vehicle payload, up and downhill driving, urban roads at low speed, rural roads at medium speed, and motorways at high speeds. The test lasts 90-120 minutes. The data collected by the PEMS seeks to verify that pollutant limits aren’t exceeded in the real world, rather than just in a lab.

Are RDE tests accurate?

Currently, PEMS isn’t as accurate as a proper lab test, so it’s only being used to verify things like NOx and won’t be used to calculate official CO2 figures. However, over the next few years, it is hoped the technology will become more reliable.
Traffic on a motorway
WLTP will help make our air cleaner

What was the NEDC test?

The New European Driving Cycle (NEDC) was previous method of testing fuel economy and polluting emissions from the exhaust pipe.
Launched in 1970 and last updated in 1997, the NEDC was also a series of lab tests but many of the results were unachievable in real-world driving. For example, if the NEDC results said a car can achieve 57mpg, a driver was lucky to see around 40mpg. The tests allowed for extras like heating, air conditioning, lights and so on to be switched off during testing, and even door mirrors could be removed to reduce drag. Fairer and more accurate WLTP tests produce more realistic figures. And WLTP results are comparable worldwide, whereas NEDC results were only valid in Europe.

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