M.C. Mehta v. Union of India (CNG Case)

Facts

• Delhi experienced severe, health-threatening air pollution
• Diesel-powered public transport vehicles, including buses, taxis, and auto-rickshaws, were identified as substantially contributing to this pollution
• Existing regulatory mechanisms, including the standard Bharat Stage emission norm progression, were not achieving sufficiently rapid improvement given the severity of the crisis

Issue

1. What judicial response is appropriate to severe, health-threatening vehicular air pollution substantially attributable to public transport, given the limitations of incremental regulatory improvement.

Held

• The Supreme Court directly ordered conversion of Delhi's public transport fleet, including buses, taxis, and auto-rickshaws, to compressed natural gas
• This conversion was required within specified timeframes
• This represented direct judicial intervention compelling a specific fuel and technology transition, targeting public transport specifically given its high mileage and disproportionate pollution contribution

Ratio Decidendi

Where vehicular air pollution reaches a severity and urgency that incremental emission standard tightening cannot adequately or promptly address, courts may order direct fuel and technology transition, particularly targeting high-impact vehicle categories such as public transport, rather than relying solely on gradual fleet turnover mechanisms.