The additional $2 billion that will be incurred by building the proposed Cross Island Line around the Central Catchment Nature Reserve instead of across it is likely to be a fraction of the total cost of the MRT project.
The Land Transport Authority (LTA), which had given the $2 billion figure in response to proposals for the line to skirt around the nature reserve, said yesterday it is unable to estimate the total cost of the 50km Cross Island Line as studies on the entire line have not been completed.
But industry experts estimate that the cost of the project could be as much as $40.7 billion.
This is based in part on calculations for past and ongoing MRT projects, which show that each kilometre of MRT tunnel costs about $350 million to $400 million to design and build.
Costs could go up by 25 per cent if eight-car trains are used, compared with the three- or six-car trains used currently.
The introduction of an express service, among other things, could also increase costs by up to 40 per cent owing to the need to build an additional track.
So the extra $2 billion for building the Cross Island Line around the nature reserve could work out to less than 5 per cent of the total cost of the project.
Nature groups had earlier raised concerns that construction work on the Cross Island Line, expected to stretch from Changi to Jurong, would have a negative impact on the Central Catchment Nature Reserve, Singapore's largest nature reserve. This is especially so if the line cuts across the nature reserve instead of skirting around it.
Having the Cross Island Line cut through the nature reserve involves building a 2km tunnel approximately 40m deep beneath the nature reserve's MacRitchie area. There would be no physical structures on the surface level.
Some members of the public The Straits Times spoke to felt that the additional cost was justified if it helped ease Singapore's transport crunch.
Those who have proposed routing the Cross Island Line round the reserve said the line would serve residents in the area and avoid disrupting the flora and fauna in the reserve.
Dr Vilma D'Rozario, an associate professor at the National Institute of Education, said: "Routing around the reserve to pick up more commuters along the way would certainly help ease road traffic congestion and sardine-packed train conditions."
Financial consultant Johnson Long, 70, believes that the additional cost can be recouped with increased ridership over the years.
Residents who live in the estates that could be affected by the skirting alignment have voiced concerns that their homes would be acquired by the state for the building of the line.
Mr Anthony Oei, 82, who has lived in Yew Lian Park for more than 50 years, questioned the need to divert the line.
"Will we have to give way to wildlife?" he asked.
Others said the possible environmental impact of the line going through the reserve should not be ignored.
Commenting on some suggestions thrown up by the public, a spokesman for the LTA said it is not possible for the stretch of Cross Island Line in question to run under Upper Thomson Road, which is near the nature reserve, owing to limited space caused by construction work on the upcoming Thomson-East Coast Line.