The Supreme Court on Tuesday sought to know if Delhi Metro could increase the frequency of its trains by reducing the time gap to one-and-half minutes instead of the existing gap of 3-4 minutes to encourage people to leave their cars and opt for the Metro trains for a pollution-free Delhi.The court also sought to know if there could be a special arrangement whereby affluent sections of people, who opt to travel by Metro leaving behind their luxury cars, were assured a seat by paying five times the normal fare.The bench, comprising Chief Justice T.S. Thakur, Justice A.K. Sikri and Justice R. Banumathi, asked Solicitor General Ranjit Kumar to seek the views of the Delhi Metro Rail Corporation (DMRC) as amicus curiae Harish Salve said that globally, the frequency of trains was one-and-half minutes whereas in Delhi it was 3-4 minutes.Asking the DMRC to consider "providing a seat to the commuter by hiking the cost (of travel)", the court said: "When car owners shift to Metro, they must have some space.""Why don't you examine it," Chief Justice Thakur asked the solicitor general.The court was hearing a matter relating to steps taken to reduce air pollution in the national capital.Salve told the apex court that world over, cleaning of Metro trains was done at night but in Delhi it was done during day time.The court will consider DMRC's response on the next date of hearing on January 20.