Delhi Chief Minister Arvind Kejriwal on Saturday said the city government was forced to take the "drastic step" of only allowing private vehicles on alternate days due to panic triggered by the increasing pollution in the capital.Kejriwal also said the measure would be implemented on a trial basis, the period of which can range from a fortnight to 20 days."There were some recent reports which said that the pollution in Delhi had increased... This caused panic and some drastic steps needed to be taken," Kejriwal said at the Hindustan Times Leadership Summit here."There is a pollution emergency in Delhi. Traffic rationing decision will be tried out for a few days. Things needed to be sorted out," he said.The Delhi government on Friday said odd and even number vehicles will ply on alternate days in the city from January 1 - a move which drew flak far and wide.The chief minister also said that from April 2016, Delhi roads would be vaccum-cleaned.Besides, grass will be grown on the roadsides, he added.