Mumbai, June 29 -- The Western Railway (WR) has received a go-ahead from the Railway Board to conduct a feasibility study for a tunnel linking Churchgate and Mumbai Central, since there are multiple constraints in laying additional tracks alongside the four existing railway lines on this stretch, officials familiar with the matter told Hindustan Times. The proposed tunnel will be used to accommodate suburban locals and segregate lines for long-distance trains, and it may be extended till Prabhadevi depending on the need and feasibility, officials said. "We will soon begin a final local survey (FLS) for the proposed rail tunnel. We will examine the requirement for this tunnel and on that basis decide the route should follow," a senior WR official said, requesting anonymity. To be sure, the cost of constructing underground rail tunnels in Mumbai, at Rs.1,100 crore per km, is nearly four times the cost of contracting elevated corridors, at Rs.250-300 crore per km. WR officials said the push for going underground was driven by multiple constraints on the existing network. "Adding more surface lines has become very difficult due to high land acquisition costs, dense urban development and litigation that often delays execution," said the official quoted earlier. "A tunnel can bypass these hurdles while creating parallel capacity and enabling the segregation of suburban services from goods and long-distance trains." The WR is already working on adding the fifth and sixth lines between Mumbai Central and Mahim, with March 2029 as the deadline. While laying the fifth line is almost complete, there has been little progress on the sixth line, officials said....