Six corridors on Diamond Quadrilateral connecting metropolitan cities and growth centers of the country (Delhi, Mumbai, Chennai & Kolkata) have been identified for feasibility studies for high speed rail connectivity viz: (i) Delhi-Mumbai, (ii) Mumbai-Chennai, (iii) Chennai-Kolkata, (iv) Kolkata-Delhi and both diagonals i.e. (v) Delhi-Chennai and (vi) Mumbai-Kolkata routes.
Feasibility studies for Delhi-Mumbai, Delhi-Kolkata and Mumbai-Chennai have been awarded in September, 2015. Feasibility studies for Delhi-Nagpur portion of Delhi-Chennai corridor and Mumbai-Nagpur portion of Mumbai-Kolkata corridor are being undertaken through Government to Government cooperation, with China and Spain respectively.