What is the RDE (Real Driving Emissions) Test?

To ensure every car complies with emissions standards it has to be tested in a lab. Originally, this process was conducted under driving conditions which used low average speeds and gentle acceleration, conditions rarely used by drivers. Since these requirements were unreflective of real world driving, it was easier for vehicles producing higher emissions to pass the test.

As a result of the flaws in the earlier testing, the Real Driving Emissions (RDE) test was introduced in September 2017 to measure vehicle emissions while they were on the road, using real-world driving to gauge how clean new cars really are.

While the RDE test initially improved the quality of emissions testing, the next step in the regulation is to enforce sterner restrictions for toxic compounds in exhaust fumes, which we know as RDE2.

This was first brought to the public’s attention in the 2017 budget announcement, where the Chancellor stated that from 1 April 2018 new diesel vehicles unable to meet the RDE2 standard would move to the higher tax band for the first year.

Understanding RDE

At present manufacturers have been given an introductory period known as ‘Step 1’ to allow them time to adjust to the stricter rules. In Step 1 vehicles are able to produce a NOx conformity factor of 2.1, whereas Step 2 will be limited to a NOx conformity factor of 1.0 with an error margin of 0.5. The error margin that features in Step 2 is to allow for the difference in lab test conditions and that of the RDE test - each test is conducted under varying road conditions.

This ultimately means that any new car entering the marketplace after January 2020 will have to meet the RDE2 standard. For new diesel cars that meet the RDE2 standard before it is introduced, they will be exempt from the higher levels of road tax introduced on 1 April, making them cost no more than a petrol car to tax.

How Does the RDE Test Work?

To test the emission levels of new cars, a piece of testing equipment – the Portable Emissions Measuring System (PEMS) – is connected to the car, via the exhaust pipe.

Vehicles are then required to drive along motorways, country roads etc. to cover various road conditions, with at least 5 minutes of the drive being at speeds over 62 mph. During this journey the PEMS kit measures the level of nitrogen oxides (NOx) as well as the tiny soot pieces often referred to as particulates.

Once this has been completed, software is used to gauge emissions figures. To get an accurate standard for all vehicles to comply to, it makes necessary adjustments to reflect weather and traffic conditions that can differ during every test.

Is the RDE Test Effective?

Through these tests alone, experts have found some diesel cars to produce NOx at alarmingly high rates, in some cases twelve times the limit of lab tests. As a result of the RDE test, vehicles like this are unable to enter the marketplace, showcasing its effectiveness in reducing the harmful emissions they produce.

Furthermore, the introduction of the RDE test paralleled the arrival of the new lab test WLTP – World Harmonised Light Vehicle Test. Under this guide, cars will be tested under more real-world conditions including, higher speeds and harder acceleration while using in car tech like air conditioning, sat navs and the radio. In doing so, officials can gather more accurate emissions data and understanding of fuel consumption which will benefit motorists looking for more accurate fuel consumption for their next car.

To keep in line with the WLTP test, cars will now need to be cleaner before going on to demonstrate they can replicate the performance on public roads under the RDE test specifications.

This test won’t impact existing cars so if you’re looking for a used car you have nothing to worry about. If you’re looking to buy your next new car soon it may be worth looking at more economical models to avoid higher costs.

If you would like to know more our sales team across our Jardine Motors Group dealerships can help.