In the late 1990s, a similar directive by the apex court led to the conversion of all non-CNG public transport vehicles to CNG.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/another-supreme-court-order-18-years-ago-and-delhi%E2%80%99s-first-brush-cng
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution-control
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cng
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicular-pollution
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/public-transport
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/cng-buses
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/public-interest-litigation-pil
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/supreme-court
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/diesel
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution