Advertisement
Tips & advice

Real-world MPG and emissions testing: What is it and how does it work?

WLTP and RDE tests measuring car MPG and emissions have replaced the older, less accurate systems used before

New systems of testing car fuel economy and emissions have replaced the previous New European Driving Cycle (NEDC) type approval tests designed in the eighties. The Worldwide harmonised Light vehicle Test Procedure (WLTP) and Real Driving Emissions (RDE) have brought in tougher real world and laboratory criteria for fuel economy, CO2 and NOx assessments in answer to criticism of NEDC.

Advertisement - Article continues below

WLTP and RDE economy and emission tests explained

WLTP has a more realistic drive cycle than the NEDC, which lasted for just 20 minutes and a total of 11km (6.8 miles) with strict speed, gear and even temperature controls. Testers cover over twice the distance on the WLTP test to get an official economy figure, while the average speed of the test has risen to 29mph (from 21mph), with a maximum of 81mph attained (up from 75mph).

Aside from longer test cycles and variable gearchanges, the checks require each car to be tested with its optional equipment; the base spec car is no longer taken to be representative of the whole range. Also, the WLTP test is supported by a real-world driving element to measure Nitrogen Oxide (NOx) emissions – the Real Driving Emissions (RDE) test.

All new cars on sale now have their fuel economy and CO2 emissions tested via WLTP and their NOx emissions via RDE1. Cars newly brought to market from January 2020 will have to meet the stricter RDE2 regulations on NOx emissions - these will then come into effect for all new cars on sale, including those originally brought to market before January 2020, in January 2021.

Are WLTP and RDE fair?

Although WLTP and RDE produce much more realistic results for fuel economy and emissions, meaning drivers are more likely to be able to achieve their car’s stated MPG, the new systems haven’t escaped without criticism.

Advertisement - Article continues below
Advertisement
Advertisement - Article continues below

The AIR (Allow Independent Road-testing) Index is an independent emissions rating system which offers a simple red, amber and green ranking system for cars based on their NOx emissions, along with a grade ranging from A to E.

The scientists behind AIR believe there’s an inherent problem with WLTP and RDE, which is allowing the car industry to continue regulating its own fuel economy and emissions figures. They argue these should be tested and graded independently.

One such scientist is Dan Carder, director of the Centre for Alternative Fuels, Engines and Emissions at West Virginia University. He led a team that published some of the earliest evidence of the Volkswagen Dieselgate emissions scandal.

When AIR launched in February 2019, Carder said: “If the AIR Index had been implemented 15 years ago, Dieselgate would likely not have happened.

“Until the recent implementation of the AIR Index, the air quality debate was devoid of objective, independent, and publicly available assessment of vehicles’ actual NOx emissions during real driving in urban environments.”

WLTP and RDE vs NEDC: Car MPG and emissions tests compared

 NEDCWLTPRDE
LocationLaboratoryLaboratory On the road
Cycle length20 minutes30 minutesBetween 90 minutes and 2 hours
Route length11.03km (6.85 miles)23.27km (14.45 miles)At least 48km (29.82 miles)
Share of test spent   
accelerating/decelerating36%84%N/A
Share of test spent   
at constant cruising40%4%N/A
Share of test spent idle24%13%N/A
Average speed 33.6kph (20.87mph)46.5kph (28.89mph)Urban (15-40kph/9-24mph)
   Rural (60-90kph/37.28-55.92mph)
   Motorway (>90kph/55.92mph)
Maximum speed120kph (74.56mph)131.3kph (81.58mph)Motorway driving has to have at least 5 mins at >100kph (62.13mph)
    
GearshiftsFixed gear positionsVehicle-specific gear positionsVaries

What do you think about the real-world car emissions testing issue? Let us know in the comments...

Get the latest electric car news, reviews and analysis on DrivingElectric.com

Advertisement
Advertisement

Recommended

The first-ever Formula E race - Motorsport Moments
Electric cars

The first-ever Formula E race - Motorsport Moments

Beijing in China was the venue for the world’s first electric single-seater series to kick off
6 Jun 2020
New Tesla Model Y 2020 review
Tesla Model Y

New Tesla Model Y 2020 review

The new Tesla Model Y has the potential to be the EV brand’s most successful model yet
4 Jun 2020
Dyson car revealed in full as time called on electric SUV project
Electric cars

Dyson car revealed in full as time called on electric SUV project

Full interior and exterior images, plus insight into the battery technology that would have underpinned British answer to Tesla
3 Jun 2020
UK electric vehicle drivers face charging point struggle
Electric cars

UK electric vehicle drivers face charging point struggle

The UK’s EV charging infrastructure is still underdeveloped according to new nationwide study
2 Jun 2020

Most Popular

New 2022 Honda Civic Type R hot hatch set to stick with tradition
Honda Civic Type R

New 2022 Honda Civic Type R hot hatch set to stick with tradition

The next Honda Civic Type R will grow in size, but it won’t use a hybrid powertrain. Our exclusive image previews how it could look
5 Jun 2020
New Tesla Model Y 2020 review
Tesla Model Y

New Tesla Model Y 2020 review

The new Tesla Model Y has the potential to be the EV brand’s most successful model yet
4 Jun 2020
New BMW 4 Series: full details, specs and pictures of the 2020 car
BMW 4 Series

New BMW 4 Series: full details, specs and pictures of the 2020 car

The new BMW 4 Series coupe has distanced itself from the 3 Series with bold styling and a huge grille
5 Jun 2020