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New emissions and fuel economy tests explained

Written by | Posted on 23.04.2018
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New emissions and fuel economy tests info

September 2017 saw the introduction of two new sets of vehicle tests: the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) and Real Driving Emissions (RDE) tests.

So, how do they work? Why have they been brought in? And what will they mean for the vehicles we drive? In this article, LeasePlan’s Head of Consultancy Services Matthew Walters answers all the key questions about these changes, to help motorists and fleets to keep up.

Why are vehicle tests changing?

These two new tests replace the New European Driving Cycle (NEDC) ones that have been in place since 1992 and were last updated in 1997. The main aim is to test vehicles under more realistic conditions and thereby produce more accurate results for fuel consumption and emissions.

What is the WLTP?

The WLTP is a new method for measuring both carbon dioxide (CO2) emissions and fuel consumption.

Like with NEDC, WLTP tests still takes place in the laboratory. However, they involve longer tests under more varied conditions, featuring more realistic driving behaviour. As a result, the CO2 and mpg figures recorded will more closely match the vehicle’s performance in real life.

When does the WLTP come into force?

WLTP came into force on 1st September 2017. All new car types now have to undergo the new tests. However, existing models are exempt for the first year. All newly registered cars will have to go through WLTP testing from 1st September 2018.

What are RDE tests?

RDE tests have been designed by the European Commission to tackle the large discrepancy between the emissions levels recorded in NEDC tests and those actually produced on the road, especially when it comes to nitrogen oxides (NOx).

As opposed to NEDC and WLTP, which are conducted in the lab, RDE tests take place on real roads. Vehicles are fitted with a Portable Emissions Measurement System and driven for 90 minutes on urban and rural roads, as well as on the motorway.

In order to be approved, new cars and vans must meet the Euro 6 standard, which sets limits for emissions of NOx, carbon monoxide and particulate matter. And, from September 2018, every new vehicle will have the Euro standard to which it has been certified displayed on its V5c registration document. That information will also be available online at the DVLA’s vehicle information service.

When do RDE tests come in?

All new car types approved since 1st September 2017 have to undergo RDE tests, but they won’t become mandatory for existing models until 1st September 2019. From that date, all newly registered cars will be subject to RDE tests.

Why is there RDE Step 1 and RDE Step 2?

To account for the uncertainties inherent in real-world testing, a ‘conformity factor’ applies to the NOx emissions measured in RDE tests.

In RDE Step 1, this conformity factor is set at 2.1, meaning that NOx emissions can exceed the Euro 6 limit (80mg/km) by up to 110%. New diesels can therefore emit up to 168mg NOx/km to meet the RDE Step 1 standard, and these will be described as ‘Euro 6d-temp’.

RDE Step 2 involves a lower conformity factor of 1.5, meaning that NOx emissions can only exceed the Euro 6 limit by up to 50%. To meet this standard, new diesels must therefore emit no more than 120mg NOx/km. Those that do so are described as ‘Euro 6d’.

RDE Step 2 will be mandatory for all new car types from January 2020, and for all newly registered cars from January 2021.

How will these new tests affect vehicle taxes?

Both Vehicle Excise Duty (VED) and Company Car Tax (CCT) rates are tied to a car’s CO2 emissions. The Government will continue to base these taxes on NEDC figures until April 2020, when it will switch to using WLTP results.

In the meantime, new vehicles that undergo the WLTP will have their CO2 emissions figures converted to ‘NEDC correlated’ figures for tax purposes, using a simulation model called ‘CO2MPAS’. As this is only a model-based estimate, NEDC correlated figures can be different to those for a similar vehicle tested under the NEDC.

For diesel cars, there is another way these new tests will affect both VED and CCT. As of 1st April 2018, new diesel cars face higher first-year VED rates than petrol ones with the same CO2 emissions – but Euro 6d cars (those that meet the RDE Step 2 standard) are exempt from this change. In addition, Euro 6d cars will not have to pay the CCT diesel supplement, which was increased from 3 percentage points to 4 on 6th April 2018.

However, as RDE Step 2 will not become mandatory for new car types until January 2020, or for other newly registered cars until January 2021, relatively few are expected to meet this standard initially. Most people buying new diesels this year will therefore have to pay the increased VED and CCT rates.

Find out more 

Read our latest whitepaper to find out more about the specific changes relating to WLTP and how it could impact fleets – or speak to your LeasePlan Account Manager.

Download a copy of our high resolution New emissions and fuel economy tests infographic here

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