Indian authorities initially planned to build a railway line from Chabahar to Zaranj, an Afghan town about 880 km away, so as to link up with the Zaranj-Delaram highway built by the Indians in Afghanistan. Once the [Indian] Railway Ministry got into the act, it assigned its external development wing, the RITES, to do a feasibility study of the project. A team of RITES came up with the findings that it would cost roughly a million dollar per km to lay the railway line and to make it economically viable, the railways would have to carry at least a million tonnes of cargo per month. The fact that the present port facility in Chabahar was not even off-loading 2 million tonnes of cargo per year and that it could take almost a decade more to reach the required tonnage for the Indian railways made the entire project unviable, even if the Indian government agreed to spend about $850 million to lay the railway track. So the project was almost shelved.
Source: India, Iran And The Story Of Chabahar, by Ravi Joshi, Observer Research Foundation, Eurasia Review, 27 October 2014.