What is WLTP? Official economy and emissions tests explained

The Worldwide Harmonised Light Vehicle Test Procedure (WLTP) is a series of official tests that aim to provide consumers with realistic information on energy consumption, CO2 emissions and electric range for new cars and vans – including petrol, diesel, hybrid, plug-in hybrid (PHEV) and electric cars. 

WLTP was first introduced in 2018 and replaced the old New European Driving Cycle (NEDC) procedure for new cars and vans, and was designed to be more accurate and representative of what you’d achieve in the real world.

As a result, the cars tested under the WLTP tests are rated on paper as being, on average, around 22% less efficient than they were under the old NEDC cycle – although, of course, they will still achieve the same results in the real world.

Instead of just testing one version of each model, the WLTP tests are carried out for every model variant, which means it applies to different engine, motor and battery options, and can even vary according to wheel size.

What is the WLTP test?

The WLTP test for fuel economy is more rigorous and complex than the NEDC tests, which were in use in one form or another since 1992. They were widely recognised as being out-of-date. 

Like the NEDC, the WLTP tests are conducted in a laboratory to ensure they’re consistently repeatable, but the challenges the car goes through are more representative of modern, real-world driving.

For instance, the test is 30 minutes long rather than 20 minutes, and it’s more than twice as long in terms of distance (14 miles rather than seven miles). On top of this, it includes a greatly reduced amount of time at a standstill (13% rather than 23.7%), a higher average speed (29mph rather than 21mph) and a regulated and more realistic test temperature (14 degrees in Europe rather than the 20-30 degree range).

It’s important to note that this test isn’t designed to tell car buyers what fuel economy they will get from a specific vehicle; the purpose is to make it easier for them to compare the fuel economy of different models. Factors such as traffic, the use of heating and air conditioning and how many people are travelling in the car will affect the mpg a car achieves. 

What Car?'s own Real MPG and Real Range tests go a step further, to give an even better indication of the economy you can expert in real-world driving.

When it comes to calculating the official WLTP range for electric cars, the testing method is slightly different, as we explain below.

What do WLTP figures mean and how are they calculated?

There are fuel/energy consumption figures for every version of every new car on sale, plus driving range stats for PHEVs and electric cars. This is because the figures vary if a car is fitted with options that affect its weight or aerodynamics, such as different size alloy wheels, for example

For petrol, diesel, hybrid, PHEV and electric cars, fuel/energy consumption and range figures are based on four different driving conditions: city driving (maximum 35mph); town driving (maximum 50mph); rural driving (maximum 60mph); and motorway (maximum 81mph). There's also an overall figure calculated from an average of the four different tests.

For petrol, diesel, hybrid and PHEVs, you’ll find the fuel economy figures for each of these sections spelt out in the technical specifications section of a car’s brochure under low, medium, high and extra high. The average across all of these figures is called the combined figure. The reason for this extra detail is so consumers have a better understanding of their car's efficiency in different scenarios (such as in town or on the motorway).

For PHEVs, which have an engine, an electric motor and a battery, the fuel economy figures are based on results when the engine is running and the battery is depleted. There’s also a weighted combined figure for the vehicle operating on both the battery and engine on a long journey.

Electric cars only have one consumption figure – for electricity used on the combined cycle (usually quoted in miles per kWh). But for range, there are two figures available for plug-in hybrid and pure electric cars: a city range based on the city and town tests, and a combined range based on all four test results. 

At What Car?, we always quote the combined WLTP range and label it the ‘official’ range to denote it as the laboratory test. However, where appropriate, we also quote our real-world range test results to give more accurate figures.

The aim of providing the data is to help consumers understand which engine, motor or battery option will best suit their driving needs.

What is the RDE test?

The WLTP test is supplemented by Real Driving Emissions (RDE) testing which, as its name suggests, takes place on public roads. These tests last 90-120 minutes and include a strict, equal measure of town, urban or rural and motorway driving. Elevation changes are also mandated, as are testing temperatures.

However, because the accuracy of the test equipment that must be carried by cars undergoing RDE tests is currently not reliable enough, authorities only use it to verify certain pollutants such as NOx, rather than calculate fuel economy and CO2 figures from it.

In time, as the equipment improves, the allowable difference between the results from the WLTP lab test and open-road RDE test will be narrowed, putting pressure on car makers to ensure the figures they declare are realistic for car owners.

How accurate are WLTP fuel economy figures?

While they provided a repeatable benchmark for comparison, one of the biggest criticisms of the WLTP fuel economy tests is that they are often difficult to match in the real world, and there’s no guarantee owners will be able to replicate the figures. Variables such as driving style, car weight and preparation, road conditions and weather conditions will play a significant role in determining what’s achievable.

This is why What Car? has been carrying out its own Real MPG emissions and economy tests for many years, and while the WLTP and RDE tests are an improvement on their predecessor, we still believe Real MPG is a better barometer of what’s achievable in the real world, as well as being a more consistent approach to testing.

Our feature outlines details on our test processes, which have been modelled and carried out with input from test experts at our private test facility.

Because they use a mapped, real-world test route in laboratory conditions they are repeatable to an accuracy of less than 2% – the variables of the RDE test cycle mean that such accuracy isn’t possible under that test cycle at present.

However, the new WLTP and RDE test figures will provide comparable analysis of every car on sale, and should act to reassure customers of the veracity of the test results.

How accurate are WLTP range figures?

Like official WLTP fuel economy tests, official WLTP range tests are conducted in laboratories so their accuracy is not guaranteed. This is why we conduct real-world tests for electric car range, in both the summer and winter, to provide buyers with more realistic figures. 

Our most recent winter range test, for example, found a range shortfall of almost 40% for some cars in cold weather conditions compared to their official WLTP range figures. 

For context, WLTP tests are conducted at a temperature of 23deg C, instead of at colder temperatures where batteries are less efficient; What Car?’s real-world testing shows an average drop in range of 18% in winter versus summer.

While the WLTP test is an improvement over the previous NEDC test, What Car? is calling for a new testing regime which provides drivers with estimates for both summer and winter conditions to ensure buyers aren’t left disappointed. However, in the absence of this, our real range testing provides drivers with figures that are more in line with what they can expect to achieve in the real world.

Even though electric cars are more efficient in warmer weather conditions, our most recent summer range test found all the participating cars were still short of their official WLTP ranges, with the largest discrepancy being 19.7% for a Tesla Model 3 RWD. The BMW i5 eDrive40, on the other hand, had a smaller shortfall of 8.1% (the smallest in the test), so it is contextual.

What do WLTP figures mean for me?

The WLTP test data is a useful source of official information; efficiency/energy use labels displayed on new cars show fuel and electricity consumption figures and the driving ranges for PHEVs and electric cars. 

The WLTP figures are particularly important if you run a company car or van because they play a part in setting the fleet car tax rate you pay.

How do I know what type of car to buy?

The WLTP tests should make it easier for you to decide whether a petrol, diesel, hybrid or fully electric car will best meet your needs. And if you need more help, our What Fuel? tool can offer advice – all you have to do is answer four easy questions. You can also check out our real-world summer and winter range tests, which we conduct every year to get accurate range results for the latest electric cars. And don't forget, once you know what type of car suits you, you can use our New Car Deals service to get a great deal on your next new car.

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