The budget is likely to approve the four remaining corridors that will complete the railways' ambitious 'golden quadrilateral', connecting the four metros -- Delhi, Mumbai, Chennai and Kolkata -- through a high-speed network, officials said on Tuesday. Two corridors of the quadrilateral -- Delhi-Mumbai and Delhi-Howrah -- were sanctioned at a cost of Rs 11,189 crore and Rs 6,875 crore respectively in the last Union budget.

The remaining four -- Delhi-Chennai, Chennai-Howrah, Chennai-Mumbai and Howrah-Mumbai -- will now be connected through high- speed corridors, with trains running at a speed of 160 kmph-200 kmph. Officials said the estimated cost of the remaining corridor is likely to be about Rs 40,000 crore. The plan is to launch the high-speed 'golden quadrilateral' by August 15, 2022, which will coincide with the 75th anniversary of the country's Independence, they said.

Once these corridors are operational, the train travel time between these metros will reduce by 50 per cent, officials said. For example, currently, the travel time from Kolkata to Mumbai varies from 26 to 40 hours. While Duronto takes 26 hours to reach Chhatrapati Shivaji Terminus, Jnaneswari Express takes 30 hours to reach Lomanya Tilak Terminus (Kurla).

With semi-high-speed trains, the travel time will vary between 10-16 hours.