A debate over how zero-emission vehicles should be defined has emerged among carmakers following the release of a policy roadmap by NITI Aayog on decarbonising the transport sector in India.

Carmakers are divided over the report's proposal to classify flex-fuel and compressed biogas-powered vehicles as zero-emission vehicles (ZEVs). The report, released last month, outlined a roadmap for decarbonising the country's transport sector.

Flex-fuel vehicles (FFVs) are internal combustion engine vehicles that operate on higher ethanol blends, while compressed biogas (CBG) vehicles run on biogas.

Maruti Suzuki, Toyota Kirloskar Motor and the Indian Sugar & Bioenergy Manufacturers Association have written to NITI Aayog supporting the inclusion of flex-fuel and compressed biogas vehicles as ZEVs in the report dated February 10th. However, rivals Tata Motors and Mahindra & Mahindra have opposed the proposal, stating that only tailpipe emissions should determine such classification.

The disagreement comes at a time when the government is evaluating the third phase of Corporate Average Fuel Efficiency norms, amid an ongoing debate over easing emission standards for small cars.

Tata Motors and Mahindra & Mahindra have stated that classifying these vehicles as ZEVs is not technically accurate, as they derive energy from internal combustion engines that produce tailpipe emissions. Supporters of the proposal state that evaluating the lifecycle emissions of different technologies and promoting domestically produced fuels could contribute to energy security.

In a letter to NITI Aayog, Toyota Kirloskar Motor stated that fossil fuel consumption and carbon emissions are the "real enemies," and that defining ZEVs using "the outdated legacy approach" based solely on vehicle tailpipe emissions would not deliver the intended outcomes.

"Realisation of actual net zero emissions by 2070 necessarily requires tackling the problem holistically on a life cycle perspective that addresses the entire value chain," the company stated.

Maruti Suzuki, in a letter dated February 26th, expressed a similar view, stating: "Moving beyond tailpipe-only metrics ensures that upstream emissions, grid composition and fuel production pathways are fully accounted for. This reflects a systems-based understanding of the decarbonisation challenge."

The company further stated that, according to the Intergovernmental Panel on Climate Change, sustainably produced biofuels operate "within a biogenic carbon cycle and do not introduce new fossil carbon into the atmosphere when assessed on a lifecycle basis." It added that this supports the classification of both FFVs and CBG vehicles as zero-emission vehicles when assessed on a lifecycle basis.

However, Tata Motors stated that including FFV and CBG vehicles under a unified ZEV framework would not be recognised under any major international standard.