What counts as a zero-emission vehicle?

A Niti Aayog report proposes classifying flex-fuel and compressed biogas vehicles as zero emission. This has sparked a debate among carmakers. Maruti Suzuki and Toyota support the move, citing lifecycle emissions. Tata Motors and Mahindra & Mahindra oppose it, arguing only tailpipe emissions matter. The government is considering this as it weighs new fuel efficiency norms.