The odd-even scheme devised by government to tackle air pollution in Delhi is "mere optics" without any substantial result, the Supreme Court remarked on Tuesday..Odd-even scheme involves having vehicles with odd registration numbers ply on roads on certain days and even registration number on other days."Have you evaluated how it worked in previous years? Such schemes are only optics," the Court said..A Bench of Justices Sanjay Kishan Kaul and Sudhanshu Dhulia further observed that the air pollution situation in the National Capital Region would have been worse had the metro railway system not been in place."An issue is extreme weather conditions. God knows what would have happened if Metro was not there. Though point-to-point connectivity is still an issue," Justice Kaul said. .The Court today also urged the Delhi government to control the entry of "orange-tagged" vehicles (polluting diesel cars) and taxis from other States in the national capital. .The Court was hearing an application regarding air pollution in the national capital, in an omnibus matter concerning various environmental issues.During the hearing on Tuesday, the bench also stated that the practice of stubble burning by farmers in the northern States of Punjab, Haryana and Western Uttar Pradesh should be stopped since it contributes significantly to air pollution in the northern region of the country including Delhi.Stubble burning refers to the practice of farmers setting fire to straw stubble that remains in the fields after the harvest of grains like wheat and paddy. The Court further noted that while the government was promoting millet on the one hand, it was also letting paddy ruin groundwater in the Punjab.The matter will be heard next on November 10.