Understanding the Real Driving Emissions (RDE) Test
The Real Driving Emissions (RDE) test was introduced in September 2017. Unlike previous testing methods, the RDE test evaluates vehicle emissions on real roads under everyday conditions, ensuring a closer correlation with actual emissions output.
With increasing concerns about climate change and air quality, governments worldwide have ramped up efforts to reduce harmful vehicle emissions. However, despite rigorous lab-based testing, earlier emission standards often fell short of simulating real driving conditions, allowing vehicles with high emissions to pass safety benchmarks.
This blog explores how RDE testing works, its impact on car manufacturers and buyers, and the advancements it introduces to combat air pollution.
Contents
- What is the Real Driving Emissions (RDE) test?
- RDE and RDE2 standards
- How does the RDE test work?
- Is the RDE test effective?
What is the Real Driving Emissions (RDE) test?
Originally, emission testing for new cars was done in controlled labs under ideal, low-stress driving conditions involving low speeds and gentle acceleration. However, these lab conditions didn't mirror the average driver’s experience, leading to a disparity between lab-certified emissions and actual on-road emissions.
To bridge this gap, the RDE test requires cars to meet specific emission standards on real roads, in real traffic with varied conditions. This approach provides a more accurate understanding of a vehicle's environmental impact.
RDE and RDE2 standards
The initial rollout of the RDE test brought significant changes, but regulations are tightening further with RDE2. Introduced during the 2017 UK budget, RDE2 set stricter limits on toxic emissions, particularly nitrogen oxides (NOx), a key pollutant linked to respiratory issues and environmental harm.
Under RDE2, new diesel vehicles must meet stringent NOx standards to avoid higher taxes. By January 2020, every new car had to comply with RDE2 standards to be sold in the market to encourage manufacturers to prioritise cleaner emission technology.
How does the RDE test work?
Currently, the RDE test includes an introductory phase 'Step 1' where manufacturers must adhere to a NOx conformity factor of 2.1. Eventually, 'Step 2' will reduce this conformity factor to 1.0, with a 0.5 error margin accounting for factors like traffic and weather.
Vehicles undergo real-world testing using the Portable Emissions Measuring System (PEMS), a mobile kit attached to a vehicle’s exhaust that measures emissions like NOx and particulate matter during on-road drives.
Testing involves diverse environments such as motorways, country roads, and city environments to mimic the range of conditions a vehicle might encounter. Part of the route requires speeds exceeding 62mph, pushing the car to perform under conditions that lab tests often fail to replicate.
The PEMS then records emissions data, which is analysed and adjusted to account for factors such as weather, altitude, and traffic, resulting in a highly accurate emissions profile.
HIs the RDE test effective?
Since its introduction, the RDE test has revealed that certain diesel vehicles emitted NOx levels many times above lab-certified limits, blocking high-polluting cars from entering the market.
Alongside the RDE, the World Harmonised Light Vehicle Test Procedure (WLTP) also contributes to cleaner emissions by simulating real-world conditions, including higher speeds, abrupt acceleration, and the use of in-car systems like air conditioning and navigation.
By using both the WLTP and RDE tests, regulators can gain a more thorough emissions insight of each vehicle, helping consumers make more informed choices about fuel consumption.
Together, these testing standards ensure cars meet both lab-based and real-world requirements before they're sold.
