The Worldwide harmonised Light vehicle Test Procedure is a bit of a mouthful, which is why it's more commonly known as the WLTP.
It sets strict rules for testing a car's fuel economy and emissions, so the mpg and CO2 figures you see advertised are – in theory – close to what you'll get in real-world driving.
What is the meaning of WLTP?
WLTP – phased in between 2017 and 2019 – is a much snappier way to say Worldwide harmonised Light vehicle Test Procedure. Let's break that word salad down.
'Worldwide' means the test is available for countries around the globe to adopt as their official testing procedure. Despite being available worldwide, it's most dominant in the UK and Europe, becoming the continent's standard for car economy and emissions measurement. It's also the standard used in Japan, South Korea and India.
'Harmonised' is an oddly poetic way to say that WLTP is a push towards balancing out different global car-testing standards. This is because the same car model might score different figures depending on whether it was tested under Europe's old NEDC standard, North America's EPA standard or China's CLTC test.
'Light vehicle' is the class of passenger cars and vans available to the general public, rather than heavy-duty trucks and commercial vehicles.
Finally, 'Test Procedure' clarifies that WLTP isn't a measurement itself. Instead, it's a set of rules that determines the procedure for testing a car's fuel economy and CO2 emissions.
What does WLTP range mean for electric cars?
WLTP range refers specifically to cars that drive on battery power – usually fully electric cars, but it also applies to plug-in hybrids. It's used as a measure of how far that car can drive on a fully charged battery.
For example, if you buy a BMW iX1 – the company's entry-level electric SUV – in the UK, it has an advertised range of 293 miles measured according to the WLTP standard. Similarly, the plug-in hybrid Audi A3 40 TFSI e is sold in the UK with a 40-mile electric range measured by the WLTP. Figures for the same cars in China and North America might be a little different due to the different measurement standards.
WLTP vs NEDC – what's the difference?
The WLTP standard was developed by the United Nations Economic Commission for Europe as a replacement for the NEDC standard.
NEDC stands – somewhat ironically – for New European Driving Cycle. This economy and emissions test procedure was developed before the turn of the millennium and is shorter and more simple than the WLTP standard. And less stringent.
The NEDC test's big drawback was that cars would often perform much better in the lab than they would in the real world. This meant buyers rarely matched the advertised mpg figures and many cars were emitting far more greenhouse gas than claimed.
WLTP aims to produce lab figures that are much closer to real-world driving. As a result, the test is longer and more thorough, featuring harder acceleration, sharper braking and higher speeds than the NEDC test, building a more representative picture of a car's efficiency.
How accurate is WLTP mpg?
The first question often asked when discussing economy and emissions testing is why the tests are performed in a laboratory. This is especially relevant when you remember the downside of most test procedures is that they produce more favourable results than real-world driving. Surely performing tests in the real world would give more accurate figures?
While it's true that tests on actual roads in regular traffic would likely return a more realistic figure for a car's real-world performance, the issue is that testers can't control all the variables. Environmental factors like temperature, air pressure and weather all have an impact on test results, as will inconsistent traffic patterns.
As a result, the only fair way to give every car a level playing field is to perform the test in controlled lab conditions, where external factors are guaranteed to be the same every time. In this sense, WLTP mpg figures are quite accurate because they let you make a fair comparison between models from different brands tested under the exact same standard.
In practice, you'll still have to work hard to match your car's claimed economy figures under the WLTP standard. That said, the difference between the advertised number and your actual economy should be smaller than it was under the NEDC system.
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