Motoring Advice

What is WLTP?

Oct 5, 2018

What is WLTP?

If you’re aware of how car manufacturers express their fuel economy and CO2 figures, you might have noticed that recently, the automotive companies have shifted from reporting their eco-stats in terms of NEDC and have instead shifted to WLTP. But what does WLTP stand for, why has it come into being and what does it mean for you as an end consumer? Here’s our guide to everything you need to know.


Since the 1970s, car buyers have wanted to know, roughly, how much fuel their car uses to cover a set amount of distance. This number is normally either quoted in miles per gallon (mpg) or litres per 100km (l/100km), and indicates how fuel efficient – or otherwise – a vehicle will typically be. In order to record these numbers and present them to potential customers, the car manufacturers therefore needed a standardised test, that would allow all of them to put their cars through a set series of driving conditions (conducted in a laboratory, to ensure equal atmospheric and temperature conditions, which might affect fuel economy otherwise) and come up with either an mpg or l/100km figure.

Thus, tracing its routes back to the 1970s, and having been formalised in 1992 before being significantly updated – for the last time – in 1997, the New European Driving Cycle, or NEDC, was born. This lab-test procedure, conducted with the subject car on a rolling road (a set of electronically controlled rollers, which keep the car in place but which allow for it to drive at varying speeds in different gears) to simulate surface resistance and with wind resistance provided by huge sets of fans, the cars were put through four repeated urban driving cycles (UDCs) and then one extra-urban driving cycle (EUDC). From this, the numbers for the car’s expected urban fuel economy (which will be lower, as urban driving is not hugely fuel-efficient), extra-urban fuel economy and its combined fuel economy (the number most often quoted in automotive literature and car reviews, this is a weighted average of the two figures previously mentioned) could all be reported.

All manufacturers who wanted to sell cars here had to adhere to NEDC and, in later years, the test started measuring CO2 (carbon dioxide) outputs from new vehicles, too, which are rated in grams per kilometre (g/km). As the world’s population became ever more concerned about global warming and greenhouse gases – of which carbon dioxide is one of the most prevalent – then CO2 figures gleaned from NEDC tests began to be used to set car tax laws in various countries. For instance, the Irish road tax laws changed from an engine capacity-based taxation system to a CO2-based system in 2008.

What went wrong with NEDC?

Dieselgate. The huge 2015 scandal, involving Volkswagen (chiefly, although other marques were culpable too), revealed that manufacturers were using sharp practices and – in plainer terms – cheat devices to get better mpg and CO2 figures from their cars during the NEDC test. Key markets like California place great emphasis on cleaner cars (i.e., ones with lower exhaust gas emissions) and so punish, via taxation, vehicles that are more polluting, and the manufacturers saw a way in which they could make their cars appear more appealing to these sorts of markets. In the fallout from Dieselgate, many big bosses at some heavyweight carmakers fell on their swords, while criminal proceedings were even undertaken in some instances.

Coupled to this shocking revelation in 2015 was a gradual loss of consumer confidence in NEDC numbers, which had been building up for years. Because the NEDC test is so short and so gentle – each car tested runs for just 11 kilometres, at an average speed of 34km/h – the figures manufacturers quoted for combined economy were often farcically high and almost impossible to replicate in the real world, with customers complaining that, as an example, turbodiesel hatchbacks that were advertised as being capable of, say, 80mpg (3.5l/100km), were more likely to return an absolute best of more like 60mpg (4.7l/100km).

Plug-in hybrid vehicles (PHEVs) particularly benefitted from the NEDC farce, as the gentility of the test cycle meant they could conduct almost all of it on their zero-emissions electric power, leading to many PHEVs quoted as having combined fuel economy of around 150mpg (1.9l/100km) and CO2 emissions of considerably less than 50g/km – giving them a huge tax advantage in countries that set up their legislation based on CO2 emissions. What was surprising and angering many early PHEV adopters was that they were driving their cars and maybe not charging them as often as they could have, and were seeing returns comparable with a diesel SUV, often attaining nothing more than 40-50mpg (7.1-5.6l/100km).

Something had to change – so the manufacturers decided to abandon NEDC and a new, hopefully more representative test, conceived by the European Union, was created: WLTP.

What does WLTP stand for?

Weirdly, the Worldwide Harmonised Light Vehicle Test Procedure, but presumably WHLVTP would have been too much of a mouthful, so WLTP it is. Like NEDC, WLTP is a lab-based test (although there’s a portion of it conducted on the public road, which is called Real-World Driving Emissions (RDE), which we’ll come back to this later) and the main procedure is more rigorous, placing more strain on the car being tested to better simulate how customers use their cars on congested roads. WLTP runs for longer, covering 23.25km at an average speed of 46.5km/h, while its rotation of low, medium, high and extra-high-speed cycles see the cars being tested hitting a peak speed of 131km/h, whereas NEDC only went to 120km/h previously. WLTP total test distance is also split 52:48 between urban and non-urban driving, compared to NEDC’s 66:34 ratio.

How has WLTP changed economy and CO2 figures?

It has made them look worse, but that’s only because they’re now a more faithful representation of what a given car will achieve in real life. For one year, from September 1, 2017, to September 1, 2018, manufacturers could quote both NEDC and WLTP figures as a ‘buffering’ changeover period was put in place, and a lot of manufacturers would quote the WLTP figures, then provide an NEDC-correlated equivalent to show that their models hadn’t suddenly all become less clean and efficient overnight – we should be absolutely clear, here, and say that no brand-new car is, in reality, any worse on fuel under WLTP than it would have been in NEDC; it’s just that you, as a customer, are being presented with economy and CO2 figures that are more realistically attainable in the real world. As of September 1, 2018, any new car being sold worldwide must have its fuel economy and emissions quoted in WLTP by the parent manufacturer; existing stocks of cars homologated under NEDC can still be sold, but only between now and January 1, 2019.

Are there any problems with WLTP?
Well, it’s still not going to be 100 per cent accurate 100 per cent of the time for all customers of a given car worldwide. Some people drive in a more aggressive fashion that other drivers, and so they’ll use more fuel and emit more CO2. Some people live in colder parts of the world and so will run more electrical systems (lights and cabin heating) more of the time, which puts a greater strain on the alternator and so reduces fuel efficiency. Some people live in hotter parts of the world and cars operate better and more efficiently in cooler air than they do in very warm conditions. Some people may live at altitude – again, thinner air means a combustion engine is not running at its optimum levels. All of these factors cannot possibly be covered by the WLTP cycle.

RDE is particularly contentious, especially with the manufacturers themselves. This is the part of the test conducted on the public road, but this is where standardisation of test procedures goes out of the window. Peugeot, for instance, will test its cars in the congested routes in and around Paris. BMW will do the same, only on the streets of Munich. Ford might use Detroit. Any of the Japanese marques, Tokyo. And the conditions, traffic flow and test routes used simply cannot be exactly the same in any of these places time and time again, nor are they comparable from one global site to another – does London have worse traffic than Barcelona, for instance?

Is WLTP the answer, then?

Maybe not, in the long-term, but it’s certainly here to stay for now – and it is a lot better than the numbers the now-discredited NEDC was delivering. And manufacturers are getting onboard – both the BMW and PSA Groups have come out to say all of their current models (BMWs, MINIs, Rolls-Royces, Peugeots, Citroens, DSs and Opels) are already WLTP-certified, meaning there will be no interruption in deliveries and sales of their vehicles as a result of the mandatory application of WLTP laws.

How will the switch to WLTP affect me?

It may, in the short-term, hit you in the wallet in a number of ways. There will be some time while the governments that use CO2-based tax legislation reattune to the shift from NEDC to WLTP, so if any cars are moving up for tax bands as a result of increased WLTP-derived official CO2 figures, they’re going to cost more to tax than they would have previously. Additionally, the WLTP test is more complex and so that costs the manufacturers more money; an increase they intend to pass on to consumers. We’ve already been told that some brands in Ireland will increase the prices of their entire product ranges by an average of around €450 to €500 to compensate for WLTP.

So is WLTP a good thing?

Oh, definitely. The NEDC scandal brought the manufacturers to task and there will now be increased honestly and openness in the industry, as companies know the penalties – both financial and in terms of customer perception – are severe if they get caught cheating emissions tests in the future. Additionally, the economy and CO2 numbers you get from a given new vehicle will be a lot closer to the figures you’re given from the manufacturer. Although, be warned, a few leading PHEVs have been tested under WLTP and their stratospheric economy and super-low CO2 figures have been (largely) preserved, so you still need to think how you will use a PHEV and how often you can charge it before buying it on the promises of its efficiency alone.