At a height of 3,300 metres, the Bilaspur-Manali-Leh railway line (498 km), once operational, would be the highest in the world, overtaking China\u2019s Qinghai-Tibet Railway. It is one of the four strategic railway lines being built by the Indian Railways to fortify India\u2019s borders with China, the others being Missamari-Tenga-Tawang (378 km), North Lakhimpur-Bame (Along)-Silapathar (249 km) and Pasighat-Tezu-Parsuram Kund-Rupai (227 km). The lines are aimed at facilitating troop and armament movement to frontier areas at short notice. With the final location survey (FLS) for the four lines \u2014 expected to cost more than Rs 2 lakh crore \u2014 in progress, the Indian Railways is expected to submit the final report to the ministry of defence by March, 2020. The mega rail projects were approved by the Cabinet Committee on Security in December, 2015. While a total length of around 1,350 km was initially estimated, the length of the railway line to Tawang would be reduced to 170 km from the earlier 377 km through the use of tunnels. Expected to cost Rs 50,000 crore, the Tawang line would have a tunnel of 30-km length \u2013 each tunnel-km of railway line costs around Rs 100 crore to build. On the other side, China has an operational railway line connecting Shigatse in the Tibet region, around 1,250 km from the Indian border. This line is expected to be extended to Dromo (close to Doklam) near Sikkim and Nyingtri in north Arunachal Pradesh. \u201cThe proposed lines are in difficult terrain and challenging geological conditions given that the Himalayas are young and fragile mountains. Though the projects are very capital-intensive in nature, no traffic is expected on these routes,\u201d says a government official. Therefore, it is the ministry of defence and not the Indian Railways that would be bearing the huge project costs, he says. Of the approximately Rs 350 crore that the surveys are expected to cost, the defence ministry has already paid Rs 150 crore to the railways. Under the final location survey being conducted, the terms of reference such as grade, loops and station locations are first decided. In the second phase, corridor trajectory is finalised and finally the design, including that for tunnels, is decided and cost estimates made. The terms of reference have been completed for all four routes. \u201cAfter the surveys are over, the railways will make a cost estimate, for the defence ministry to provide the final go-ahead,\u201d the official says, adding actual spending on the projects would start with geological investigations. The railways is using advance techniques such as photogrammetry, drone survey and digital elevation models for the survey. It will take another five years for the lines to be constructed once the survey reports are submitted.