Private cars will be allowed on the streets on alternate days from April 15-30 based on even or odd licence plate numbers, Arvind Kejriwal, the city's top elected official, said Thursday.

The first phase in January was welcomed by people but couldn't be done permanently because the city's public bus system is inadequate, Kejriwal told reporters.

The advocacy and research group Centre for Science and Environment lauded the formula and said air pollution after the January trial returned "with a vengeance.'"