My Urban Car

Euro 6 vehicle testing gets more realistic with WLTP RDE and RDE2. What are they?

The discredited Euro 6 emissions regime is changing with the arrival of WLTP & RDE1 tests. Meanwhile UK Government has decided (vehicle excise duty) rates on new diesel cars from April 2018 would be based on the RDE Step 2 standard, RDE2 which hasn’t even arrived yet. How does this affect you?

The 2015 Euro 6 standard in theory has an 80 mg/km limit for NOx emissions. In reality the lab based test (called NEDC) was so flawed and widely abused that on average Euro 6 diesels emit over 5 times this amount (420mg) and the worst emit 19 times the limit (1,500 mg/km). They are sold to consumers as “clean diesels”. These cars produce around 7x the NOx of a petrol cars and the worst are up to 25x more polluting.

The new Euro 6 from regime requires slightly more realistic testing of all new cars from Sept 2018.

WLTP – This is a slightly more demanding lab test regime that should produce economy and emissions figures closer to what drivers can achieve on the road. In reality it’s brought good and bad news.

The good

  • All Cars sold after Sept 2018 have to pass WLTP lab tests
  • The very dirtiest diesels (those over 20x as polluting as a petrol ) have struggled to pass the test and some (like the Fiat 500x diesels) have been removed from sale.
  • The figures are closer to being realistic.
  • Some cars will now be cleaner. Petrol cars which produce very little toxic NOx pollution but did produce particulate pollution are now finally getting fitted with filters that make them super clean for both main risks to health. Likewise some filthy diesel models are finally being fitted with Adblue cleanup systems.

The bad

  • WLTP testing takes longer -not only is the test longer, every version and option that affects the results (eg size of wheels) has to be tested separately. The backlog has meant many models have had to be removed from sale just because they haven’t been tested yet.
  • existing dirty diesels don’t have to pass the RDE 1 test until September 2019. So diesels up to 20x as polluting as a petrol car remain on sale with no warnings for consumers (unless they use the MyUrbanCar app or other real world emissions data)
  • While some dirty models have been withdrawn even more clean models like petrol hybrids from VW group have been removed from sale.
  • Rather amazingly in EU land once they test more realistically for things like CO2, they put the result in a computer than converts it back to the what the old unrealistic lab test would have produced. Yes.. honestly. It’s called NEDC equivalent. The car is then advertised and taxed on this not the more realistic figure. This situation carries on till 2020.


RDE tests require cars to pass an on the road test with portable equipment (called PEMs) strapped to the back to measure everything that comes out of the exhaust as it is driven for minutes or hours on the road. It isn’t perfect but one can hope that RDE tests will bring real emissions for diesel cars to within 10% of the official test results.


As around 90% of diesels would fail the RDE1 test if they were required to achieve under 80mg/km in the real world, the EU allowed a car to pass if it came within 210% or 2.1 times the 80mg limit. ie on RDE  1 or step 1 a car passes the test if it achieves under 168mg/km. If you still assume a little bit (10%) of manipulation by carmakers then 185mg on the road, still a big improvement on Euro 6 but over double the official limit.

RDE1 only becomes a requirement for all cars even with 168mg limit from Sept 2019. Until then new models have to pass the test but existing dirty diesels remain on sale.

Update: a court decision in december 2018 found the EU acted illegally in raising pollution limits in a real world test. This may mean diesels have to pass the 80 mg in a real world test. This really would force the dirtier models to be removed from sale. The ruling could essentially replace the 163mg RDE1 limit and 120mg RDE2 limit with the 80mg maximum allowed under Euro 6- but diesels would have to achieve it on the road not just fake it in a lab test.


RDE step 2 reduces the lobbying factor to 50% and is due to start in 2020. This means a max on test of 120mg/km or 132 g/km assuming 10% manipulation. It was only due to be a requirement from Jan 2020/21. This is the standard now being used to decide vehicle excise duty in the UK.

Manipulation options still available include choosing the test track used and weather conditions and choosing the individual car to be tested (ie not a random selection)

Expressed as “petrol car’s worth of pollution” (60mg/km that most petrol cars comply with) a diesel car could emit as much toxic NO2 as :

  • 32 petrol cars before September 2019 under Euro 6,
  • 3 petrol cars for new diesel models launched after September 2017 under RDE1 
  • a max of just over 2 petrol cars to comply with the latest RDE2 standards to be defined as clean for the April 2018 (Vehicle Excise Duty) VED table.
  • a max of 1.3 petrol cars worth of pollution if the court decision is upheld and the limit is set to 80mg

Why The UK gov using RDE 2 for vehicle excise duty matters – ULEZ Zones

What the Chancellor has done is rather quietly (and in his speech very vaguely) established RDE-2 as the official measure of what is a clean diesel. It’s not perfect but several years ahead of rest of the EU. What cities and councils across the UK should be asking themselves as they debate clean air zones is this – If a clean diesel for VED is RDE 2 then should that also be the standard for what is a clean diesel in a clean air zone or ULEZ? This opens up Euro 6 diesel even on step 1 to being subject to limits and charges. So the question is when will the Mayor of London and others try out the new emissions standard as a requirement of a clean car and how soon?

To be clear on this Euro 6 (both dirty and clean) are allowed to be sold for 2 more years but there is a strong risk they will no longer be officially seen as clean. Which is fair as most aren’t but they are still on sale now.

Another issue is that there are around 15% of cleaner diesel cars on sale have been independently tested as compliant with the Chancellors 120mg /km limit, but unless carmakers submit them for an official RDE2 test they still will be hit for not being compliant with the standard. No diesel currently on sale has been tested on or passed RDE2.

There is a substantial chance that only a handful of diesels (if any) will be officially RDE2 compliant by next April. Food for thought.

Short term effects of the announcement

The DVLA will need to add a field for RDE2 pass / fail on registration docs and information about cars. The current assumption is the actual test result won’t be provided but this could change.

In the UK (because cars need to achieve RDE2 to avoid stepping up a band for CO2) the RDE1 168mg limit is likely to be passed over as makers aim to pass RDE-2 120mg limit. As the average Euro6 diesel produces around 480mg of NOx the new standard will finally sift truly clean diesels from those that are clean in EU lab tests but filthy on the road.

Car industry groups have pushed back against the proposals to use the RDE2 standard on three grounds:

  1. that this “punishes diesel drivers”. Not really adding much as a point. Diesel drivers aren’t some persecuted religious cult, they’re just car drivers who choose to buy a new diesel car after April 2018. If diesel isn’t tax efficient any more they will just choose another fuel.
  2. That the lack of notice means they haven’t had time to develop cars to meet the standard. Well lets face it Euro 6 has required a maximum of 80mg/km of NOx. So complaining that 4 years later cars actually have to achieve 120mg/km on the road (50% more than the limit they were meant to have met 4 years ago!) seems a little odd. In any case around 15% of new cars have been independently tested as being below RDE2 NOx levels on the road. So cars can already meet it and have done for years in the United States. Which brings us onto the third point.
  3. The RDE2 test doesn’t exist yet! RDE2 is an EU test that wasn’t due to begin till 2020. In addition to a lower NOx limit than RDE1 it also tightens up some of the test requirements to reduce potential manipulation. Industry groups claim ( and they may be right ) that there isn’t a final approved RDE2 test that can be officially taken yet. Obviously it would be wrong if cars able to pass RDE2 can’t take the test because it’s not ready.
    If that is correct then a logical compromise might be that cars achieving under the 120mg/km limit during an RDE1 test should be considered clean under the VED proposals. Carmakers would then have the choice of submitting cleaner diesels for RDE tests to achieve the tax benefit.

Government notes on the new policy are available here

VED changes

Company Car changes

David Nicholson

David Nicholson Is the founder of Rivergecko Ltd & MyUrbanCar which provide consultancy and advice for drivers and fleets to speed the transition from dirty fossil fuel transport to clean vehicles powered by renewable energy on land water and air.

The @MyUrbanCar twitter feed is a source of news & reviews of electric & plugin cars and vans in the UK.
The @rivergecko twitter feed & websites bring news and opinion on cleantech transport including cars, vans, buses, trucks, shipping, rail & aviation as well as autonomous vehicles & renewable energy, air pollution & motor industry news.

David Nicholson has worked as an underwriter at Lloyd's of London since the 1980's. His interest in technology goes back many years including interactive mapping, apps, green tech, boats, solar and cars.