The Delhi government plans another round of tough measures to restrict the use of private cars and clean up toxic air in the Indian metropolis, the world's most polluted city.From April 15, for two weeks, cars will only be allowed on the road on alternate days, going by whether their number plates are odd or even, Chief Minister Arvind Kejriwal said on Thursday."We are seriously considering if we can do this for 15 days every month," Kejriwal said. "We can't do this on a permanent basis until we get better public transport." The rule hits most of the 2.6 million cars that ply the traffic-choked roads of Delhi and its surrounding areas. Kejriwal said his plans had overwhelming public support and were necessary to rein in the rising levels of air pollution that regularly cloak the city in smog.