MUMBAI, July 15 -- Mumbai could get its first underground suburban railway station, at Byculla on the Central Railway, if plans for an underground corridor between Parel and CSMT get the green signal. The underground corridor is part of one of Mumbai's biggest suburban rail expansion projects that is seeing the addition of the fifth and sixth railway lines along the 17.5-km-long Kurla-Parel-CSMT stretch, to segregate suburban and long-distance services. While Phase I between Kurla and Parel is underway, the second phase, from Parel to CSMT, is being studied. The Mumbai Railway Vikas Corporation (MRVC) executing the project is considering an underground tunnel for the fast suburban corridor between Parel and CSMT, with a halt at Byculla, mainly to circumvent land acquisition challenges. "We have appointed a private consultant to study the feasibility of the project," said an MRVC official. Japanese consultancy firm PADECO will examine the project's engineering feasibility, geological conditions, proposed tunnel's alignment and other technical aspects. It will also study the feasibility of developing an underground suburban station at Byculla. If the plan goes through, the existing station at Byculla will continue to service the slow corridor. Railway officials say suburban trains are better suited to underground operations than long-distance trains as they can negotiate relatively steep gradients. An MRVC official said the proposed tunnel could be built 20 to 25 metres beneath the existing railway corridor, eliminating the expensive proposition of acquiring fresh land. Sources said the feasibility study will examine Mumbai's metro rail network, particularly the proposed Metro 11 between Wadala and Colaba, which will include an underground stretch from Byculla to Nagpada, Bhendi Bazaar and CSMT. Engineers will study how the corridor plans to navigate power cables, storm water drains and other utilities. The idea of an underground stretch between Parel and CSMT gained momentum with the CR after the Mumbai Metro Line 3 was built, the city's first underground metro corridor. "The metro project demonstrated that large-scale tunnelling is possible even in the most congested parts of Mumbai. We are now examining whether a similar approach can be adopted for suburban railway lines," said a senior CR official. The railway estimates that nearly 550 project-affected persons would need to be rehabilitated if an above-ground corridor is built. The project to add the fifth and sixth lines from Kurla to CSMT was originally sanctioned in 2008 at an estimated cost of Rs.890.89 crore. It has since escalated to around Rs.1,337 crore. The underground option could more than double the cost, to around Rs.3,000 crore....