Early 2013: The Land Transport Authority (LTA) announces the 50km Cross Island Line to link Changi and Jurong by 2030.
Preliminary plans show it cutting through primary and secondary forests in the Central Catchment Nature Reserve.
Nature groups, alarmed by the possible environmental harm, suggest that the line be built along Lornie Road on a route that goes around the nature reserve.
September 2013: The LTA announces an environmental impact assessment (EIA) to study both alignment options.
August 2014 to December 2015: Consultancy Environmental Resources Management works on Phase 1 of the EIA, which looks at the potential impact of site investigation works on the nature reserve.
February 2016:The LTA gazettes the findings of the EIA's Phase 1.
They show that tests to see how a train tunnel can be built through the nature reserve would have a "moderate" impact on plants and animals there, but only if measures to reduce impact are strictly implemented.
Otherwise, the soil investigation works for the upcoming Cross Island Line could have a large impact on the highly sensitive parts of the nature reserve.
Mitigation strategies to prevent this include the use of enclosures to reduce engine noise and tanks to collect discharge.