Cleaner vehicles and better monitoring: New RDE regulations on light-duty vehicles in India

This piece originally appeared in The Financial Express.

At the start of this month, India implemented Real Driving Emissions (RDE) regulations for passenger cars that require vehicles to meet emissions limits during on-road driving in addition to laboratory test conditions. The RDE testing in India involves a range of conditions for various testing parameters and this is a positive step that can be traced back to the “Dieselgate” scandal, which affected the automotive business worldwide and led policymakers to adopt tighter regulations and revamp testing methods.

The RDE norms will cover more of the actual driving conditions in India and reduce the gap between emissions during lab tests and real-world driving emissions. That’s important, and we also suggest that Indian policymakers work to set a timeline to phase out the conformity factors that are currently in place, as Europe has already done. Having a timeline will make clear to manufacturers that they will need to plan and make investments to produce compliant vehicles.

What is a conformity factor and where does it come from? Well, things like vehicle speed and ambient temperature are kept within a specific range during laboratory tests, to ensure they are replicable. However, as mentioned above, RDE testing will involve a range of conditions for various testing parameters, and some driving conditions that are typical of real-world use might not be covered under the RDE protocol. To conduct tests for those conditions, portable emissions measurement system (PEMS) testing is used. Due to uncertainties in the actual on-road driving conditions and with the PEMS instrumentation, real-world emissions are assessed more leniently than lab limits. The conformity factor is a scaling factor used to adjust the limits in the Bharat Stage 6 (BS 6) emission standards to allow higher emissions in real-world driving conditions than are allowed in the laboratory.

Does this mean that conformity factors allow vehicles to emit more than the emission standard? Yes. If the conformity factor for nitrogen oxides (NOx) emissions is set at 1.43, that means the emissions from a vehicle during real-world driving can be 43% higher than the standard the vehicle must meet during laboratory testing. To reduce the time that higher emissions are allowed, European policymakers are set to reduce their conformity factors later this year and have proposed to eliminate them altogether in a couple of years. As Table 1 shows, Europe is proposing that by 2025, all on-road emissions from light-duty vehicles measured during RDE testing should not exceed the laboratory tests under the boundary conditions of the RDE standards.

Table 1. Comparison of conformity factors (CF) for NOx and particle number (PN) between India and Europe

Pollutant India CFa Euro 6d CFb Euro 6e CFc Euro 7 CFd
NOx 1.43 1.43 1.10 1.0
PN 1.5 1.5 1.34 1.0

(a) In effect since April 1, 2023. (b) In effect for type-approval tests since January 2021. (c) Set to take effect for new type-approval tests in September 2023 and for all new vehicles in September 2024. (d) Proposed to take effect starting July 2025 for new LDVs.

India’s new RDE regulation will significantly impact diesel vehicles because those require aftertreatment technologies such as lean NOx trap (LNT) and selective catalytic reduction (SCR) to limit pollutant emissions during real-world driving. So far, manufacturers selling in India have used LNT, the cheaper option, on most models. But now that there is a need to also meet emission limits during real-world driving, LNT is at a disadvantage because the real-world emissions are significantly higher even after applying conformity factors. This happens because LNT is sensitive to changes in exhaust gas temperature, and such changes can impair the catalyst’s ability to store and decrease NOx emissions, especially when temperatures vary greatly. SCR, the more expensive option, reduces emissions significantly but necessitates using a urea-based solution that must be stored aboard the vehicle and replenished regularly.

SCR technology has been shown to be highly successful in reducing NOx emissions, even in difficult driving conditions like high-altitude or low-temperature environments, but cost is an issue. While most diesel SUVs in India have used this system since the BS 6 norms were introduced, cars with smaller diesel engines (those below 2.0 liters) have used an LNT system to control pollutants. If makers of the smaller vehicles replace the LNT with SCR, it’s unlikely they will be able to sell their vehicles at competitive prices, and some of the models are already being pulled from the market.

Still, phasing out compliance factors is necessary for the real-world emissions reductions that will contribute to a healthier environment in India. Automakers will need to plan to use technologies and strategies that do not rely on conformity criteria, and knowing when conformity factors will be phased out will signal to them to plan for the future by investing in effective technologies.

India’s RDE norms will also bring in stricter compliance and enforcement, and manufacturers might be obligated to conduct a recall or take other corrective measures to bring a vehicle back into compliance if it is discovered to generate more pollution than laws permit. Such policies ensure that automobiles meet emissions requirements throughout their lifetimes, rather than only during initial laboratory testing. This is particularly important because cars lose efficiency and produce more pollutants as they age.

Overall, the introduction of RDE testing is expected to lead to better monitoring of vehicle emissions, increase the quality of vehicles being sold, and reduce the scope for manufacturers to evade accountability for emissions. Bringing the conformity factors to 1 would do even more to reduce air pollution and improve public health outcomes in India. Due to the cost of compliance for manufacturers, vehicle models that cannot satisfy RDE requirements without more expensive technology are likely to be discontinued.