India, Nov. 1 -- From Sunday, November 1, Delhi will turn back vehicles registered outside the city that do not meet BS-VI emission standards. The restriction is part of the revised Graded Response Action Plan (Grap), Delhi-NCR's winter pollution-control plan, and runs until January 31, 2027.

The numbers are large. Transport department estimates put the number of vehicles below BS-VI across Gurugram, Faridabad, Noida, Greater Noida and Ghaziabad at more than a million. Gurugram and Faridabad account for nearly 200,000, about 70% of them BS-III and BS-IV, along with around 50,000 commercial vehicles. Noida and Greater Noida together have more than 400,000 vehicles below the standard, more than half of them BS-IV petrol cars.

That does no...