Tougher emissions tests come into force from today

Stricter testing procedures are set to provide UK car buyers with more accurate fuel economy and emissions information from today (01 September). Two new test regimes come into force - WLTP and RDE - with both providing more accurate data than the existing NEDC test that is widely regarded as unfit for purpose.

It is because of the New European Drive Cycle's (NEDC's) lack of realistic testing that drivers often cannot come close to their car's quoted fuel economy figure. The gap between quoted official figures, and those found in the real world has been increasing from an average of around 7% a decade ago to over 40% in 2017.

To improve the accuracy of the data, the Worldwide Harmonised Light-Duty Vehicles Procedure (WLTP) cycle and Real Driving Emissions (RDE) tests have been developed. The WLTP, which has been in the pipeline for over a decade, provides data obtained in a similar way as NEDC, but with more realistic drive cycles.

Both the NEDC and WLTP test are conducted on a 'rolling road' in laboratory conditions; though the WLTP is a longer test, and with a greater degree of variance in drive cycles. For example, engine speeds are changed more often, with greater variance in the acceleration and braking phases. Likewise, more load is put on the engine, there are more gear changes, and a greater range of temperatures are taken into account.

The new WLTP drive cycles are based on analysing half a million miles of real driving data, and more accurately reflect the fuel economy and emissions figures actually found by drivers. However, during the time it has taken to agree globally, the WLTP has itself become outdated with some analysts estimating that it will continue to differ from most real world. It is also designed for all global regions rather than being closely matched to any one country's driving style.

Comparing the NEDC and the WLTP figures, Jelica Pavlovic and colleagues based at the EC's Joint Research Centre have concluded that: "WLTP-based CO2 figures will be around 15% higher than the current type approval values, potentially halving the current gap between type-approval and in-use fuel consumption". In other words, while an improvement, the WLTP data will still not match most drivers experience of their car's CO2 emissions or fuel economy.


Source: SMMT

More encouragingly, Real Driving Emissions testing offers even more accuracy than WLTP. As the name suggests, the tests are carried out on real roads, in public, and with a Portable Emissions Measurement System (PEMS) attached to the car as it is driven around a set route.

The RDE testing takes in a variety of different situations, including motorway, open roads, and urban driving, with a reasonable weighting for each. The tests are as accurate as a standardised procedure is ever likely to be - other than a future possibility (see below) in which live and constant data is fed back from all vehicles in real time.

The introduction of RDE was a direct result of the VW Emissions Scandal, with EU leaders deciding that, although the WLTP was due to come into force anyway, a more accurate still test procedure should be implemented to better forecast both fuel economy, CO2 emissions and, most importantly, NOx emissions.

With the aim of providing the best possible information to car buyers, Next Green Car already includes RDE data when available within its data set, the real-world figures being supplied by data partner Emission Analytics which has developed the industry standard 'EQUA Index' for fuel economy and emissions. Look out for the EQUA logo where this data is available for a particular model.

Although the RDE test is the more accurate of the two, the WLTP programme still has a role to play, as it continues to provide a degree of comparison for MPG between models over more drive cycles. Next Green Car will also be adding WLTP data to complement the NEDC and RDE figures already quoted on the website.

By design, the implementation of both tests will see 'worse' economy figures from new models than when compared to their predecessors. In fact, the figures will be more accurate, and so although the numbers will go down in the case of MPG, and up in terms of emissions, it does not actually mean that cars are less efficient, only that the data better reflects the actual performance.

While the WLTP data will start to be published by car manufacturers from today, regulators are allowing a two-year roll-out period for the release of the data with all OEMs having to comply by September 2019. In the meantime, figures for NEDC, WLTP and RDE tests will be published alongside each other - possibly causing as much confusion as clarity regarding vehicle MPG and emissions.

RDE and WLTP comparison

Source: Next Green Car (While some image elements are courtesy of ICCT, image additions are responsibility of NGC)

Each car maker has taken a different attitude to the release of WLTP and RDE data with the most forward looking companies being first to be transparent about the performance of their cars. Most upfront has been the PSA Group - which comprises Peugeot, Citroen, DS Automobiles - which has been publishing RDE figures for some time. The company also now includes Opel/Vauxhall, though only as of recently, and too soon for tests to have been carried out and data placed in the public domain.

While the new, more accurate test programmes are to be welcomed, Next Green Car believes that more can be done. As explained by Dr Ben Lane, director of the company: "While WLTP was a good solution when it was proposed a decade ago, it now fails to close gap between test and actual MPG as the car companies have become ever better at beating the tests. RDE is a much smarter approach but it will take several years all new models to be tested by real drivers on real roads.

"In the long term, NGC supports a new approach, namely Continuous Vehicle Emissions Monitoring (CVEM), whereby the emissions from all cars are monitored in real-time, all the time. This would replace the current testing regime which involves the testing of a small number of test cars soon after they leave the factory. Only CVEM offer drivers and policy makers with the data they really need."

Find out more about emissions here

Download PDF of the white paper jointly published by Next Green Car and NXP Semiconductors: Continuous Vehicle Emissions Monitoring (CVEM)

Ben Lane

Author:Ben Lane
Date Updated:1st Sep 2017

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