Real Driving Emissions tests: What is RDE2?
When the Chancellor announced the tax hikes that hit new diesel cars this year, he made a special exception for ‘RDE2 diesels’. But what are these entities with such an obscure acronym? Some new kind of Star Wars droid, perhaps?
Not quite. To understand what RDE2 means, we need to start with the RDE part: Real Driving Emissions.
What is the Real Driving Emissions test?
The Real Driving Emissions test is a new procedure for measuring the pollutants given off by a vehicle. It was designed by the European Union to address the problem of harmful NOx emissions being significantly higher on the road than in the New European Driving Cycle (NEDC) laboratory tests.
For example, the latest Euro 6 emissions standards specify that diesel cars registered from 1 September 2015 cannot emit more than 80mg NOx/km, yet real-world testing by The Real Urban Emissions Initiative has revealed that they actually emit around 400mg/km on average.
The new RDE test takes place on actual roads – using a portable emissions measurement system fitted to the car – rather than in the lab. It came into force in September 2017 for new models and will apply to all newly-registered vehicles from September 2019.
So that’s RDE. But what about RDE2? Before we get to that, we need to tackle another concept: the ‘conformity factor’.
What is a conformity factor?
The conformity factor is essentially a way of giving manufacturers time to adapt to the new, more stringent RDE tests. It effectively raises the Euro 6 NOx limit so that diesels can emit more than 80mg/km and still be approved for sale.
Initially, a conformity factor of 2.1 applies for the first two years of RDE tests. This means that the true limit is 80mg/km multiplied by 2.1, or 168mg/km. From January 2020, new models of car will have their conformity factor reduced to 1.5, meaning that they can emit no more than 120mg NOx/km. That lower conformity factor will apply to new cars of all models from January 2021.
And that’s where we get to RDE2, which is short for Real Driving Emissions Step 2. To meet the RDE2 standard, a car must meet the Euro 6 NOx limit with the lower conformity factor of 1.5. In other words, it must be shown, in the new RDE test, to emit no more than 120mg NOx/km.
As explained above, all new diesel cars will have to meet the RDE2 standard from January 2021, and some released before then may well meet it, too. These are the ones that the Chancellor has exempted from his tax increases earlier this year.
As of April, new diesel cars face higher first-year Vehicle Excise Duty (VED) rates than petrol ones with the same carbon dioxide emissions – except for RDE2 diesels. Similarly, RDE2 diesels are exempt from the diesel supplement for Company Car Tax (CCT), which rose from 3% to 4% this year. Essentially, RDE2 diesels will be treated as if they were petrol cars for VED and CCT purposes.