Car makers operating in the European Union have begun using the new Worldwide harmonised Light vehicle Test Procedure, or WLTP for short, to calculate fuel economy figures.

What is WLTP?

WLTP serves as a replacement for the New European Drive Cycle (NEDC), which was developed in the 1980s and has been in use throughout Europe since 1996.

Like NEDC fuel economy numbers, WLTP figures will begin appearing on the pages of CarAdvice when we cover news of, or drive, new and updated cars originating from Europe, before these vehicles are tested using Australia's ADR 81/02 fuel economy procedure.

Developed with heavy input from European automakers, WLTP uses data about driving styles and is designed to better reflect real world situations.

Compared to the NEDC, the WLTP cycle runs for a longer period: 30 minutes compared to 20 minutes. The cycle distance is also significantly longer at 23.25 kilometres, compared to 11km for NEDC. Shift points are also now calculated on a per-vehicle basis.

During a normal cycle, a car goes through laboratory tests mimicking low, medium, high and very high speed driving situations with stopping, acceleration and braking. Mathematical models will be used to calculate differences in fuel economy for low and high spec trim levels.

As it is a bench-testing regime with strictly defined parameters, WLTP still doesn’t take into account common variables, such as aerodynamics and operation in different climates, but it does include mathematical adjustments for optional equipment.

New models introduced in Europe from the beginning of September 2017 are required to be tested under the new WLTP regime, with all vehicle registrations from September 2018 required to have a WLTP rating, although there are some exceptions for unsold cars reaching the end of their product cycle.

Despite its name, WLTP is only legally required for cars being sold within the EU for now. WLTP figures will not only be used for informational purposes to aid comparative shopping and calculating corporate fuel economy numbers, but, depending on the jurisdiction, can also be used to determine sales tax, annual road taxes, and registration classes.

If WLTP is adopted by countries outside of the EU, there is leeway for them to modify the test procedure to account for different driving styles, and road and atmospheric conditions.

It remains to be seen how well WLTP reduces the gap between typical real world fuel economy figures seen by drivers and the official numbers ascribed to vehicles.

According to the International Council on Clean Transport, the discrepancy between real world and measured values grew from about seven per cent in 2001 to 30 per cent by 2013.

What about RDE?

WLTP should not be confused with RDE (Real Driving Emissions), which is a real world emissions testing regime being adopted gradually in the EU between now and 2019. In time, RDE will be used to determine a vehicle's compliance, or otherwise, with the EU's rules on emissions.

To complete their RDE test, cars are fitted with a Portable Emission Testing System, a bulky system that plugs into a car's exhaust system and measures its output.

During the RDE test, a vehicle is driven for a significant period of time on a variety of roads, including high speed motorways, medium speed rural roads, and low speed urban roads. There are also rules requiring elevation changes, temperature variations, and extra loads.

While RDE can give a more realistic picture of a car's real world fuel economy and emissions output, numbers from RDE testing aren't comparable between cars or even between tests on the same vehicle because it's almost impossible to account for all the variables that come about from testing on public roads, such as traffic, specific atmospheric conditions and driving styles.

And what about Australia?

At the moment, Australian cars are tested using the ADR 81/02 cycle. The testing takes place over 20 minutes, with 33 per cent of the process dedicated to extra-urban driving and 67 per cent dedicated to urban testing.

As is the case worldwide, the number on the sticker rarely matches the number you'll see on the dashboard display, and the Australian Automotive Association (AAA) wants to change it.

The AAA has been vocal in its criticism of the gap between real-world and lab-test efficiency, which it says averages around 23 per cent. The worst car in its testing, conducted as part of a report it calls Welcome to the Real World, used 59 per cent more fuel in the real world than its claimed figure.

To try and close the gap, which it labels as misleading, the Association wants to introduce real-world emissions testing to Australia. The suggested test would be a version of the current New European Drive Cycle (NEDC), adapted to suit local driving habits with higher urban speeds, lower highway speeds and a warmer climate.

Above: A look at the AAA findings 

"More stringent emissions laws are meant to reduce pollution and drive down fuel use, however our results suggest such benefits largely occur only in the laboratory," Michael Bradley, AAA Chief Executive, said.

"Popular cars on the Australian market are using up to 59 per cent more fuel than advertised and emitting more than seven times the legal limit of some noxious emissions.  It’s becoming clear that as emissions standards tighten, the gap between laboratory results and real-world results is widening, meaning consumers and the environment are increasingly being ripped off."

Tony Weber, Chief Executive of the Federal Chamber of Automotive Industries (FCAI), has a different take on the Real Driving Emissions (RDE) testing used by the AAA.

"Simplicity in a headline doesn't actually translate to clarity of decision-making for consumers," he said of the AAA's media campaign around RDE.

Above: The FCAI roadmap to Euro 6 in Australia

"My concern with RDE, as illustrated by the testing undertaken by the AAA, is the fact that it can be quite misleading," Weber told CarAdvice. "The testing undertaken by the AAA was one-third suburban, one-third rural and one-third highway.

"If that is your driving profile, then the RDE can be very useful to you as a consumer when you go to buy your car. But the problem for me... I am probably about 99 per cent urban, and the other one per cent is divided between rural and highway. The headline number from that test doesn't give me much of an indication about what is the appropriate car for me."

Weber also argued current testing, although not perfect, serves its purpose as an 'apples-for-apples' comparison of new cars. He was also keen to point out other issues with our current emissions rules, including low-quality fuel.

"The standardised testing, which is the Australian Government test, is an apples-for-apples comparison of two vehicles under laboratory testing," Weber said.

"It might not be what you get in the real world, but it is an apples-for-apples comparison. If you have two options in selecting a new vehicle, you can compare them in that laboratory environment on a consistent basis."

He didn't, however, completely dismiss the notion of RDE testing working in the future, albeit with more refinement.