A tender to study the environmental impact of the Cross Island Line on the Central Catchment Nature Reserve will be called on Monday, the Government said in a press statement.
It expects to hire a contractor by the second half of the year and the study to be completed by 2016.
The 50km Cross Island Line, to be completed by 2030, will connect eastern and western Singapore and serve as an alternative to the East-West Line.
Nature groups here including the Nature Society had expressed concern that a part of the line - apparently slated to cut through the nature reserve - would hurt the reserve's flora and fauna. The Government has said the train line's alignment is not finalised.
The Land Transport Authority's chief executive Chew Hock Yong said in the press statement that it had worked with residents and nature groups over the past eight months to address their concerns.
"LTA is also mindful that there are other stakeholders who may have concerns over the alignment options, and therefore this environmental study is only one of the inputs that will be considered before an eventual decision is made on the alignment," he said.
The LTA added that it would also call a tender for an engineering feasibility study for the Cross Island Line. This is expected to start in the second half of the year and be completed by 2016.