The 50km Cross Island Line (CRL) will be an important part of Singapore's rail network, Transport Minister Khaw Boon Wan said.
Nearly half of its 30 stations from east to west will be interchanges to other MRT lines, offering commuters many travel options, he added.
Mr Khaw told Parliament yesterday that the line will serve residential areas such as Loyang, Pasir Ris, Hougang, Ang Mo Kio, Sin Ming, Bukit Timah, Clementi and West Coast, and commuters will make at least 600,000 trips on it daily.
But as to whether the underground CRL will be built through the Central Catchment Nature Reserve (CCNR) or route around it - an issue of contention - Mr Khaw said more environmental and engineering studies, along with public consultations, must be done.
These may take over two more years, before a decision on the alignment can be made, Mr Khaw said, in reply to questions from Mr Louis Ng (Nee Soon GRC) about the CRL.
An Environmental Impact Assessment (EIA) report to study the effects of site investigation works, released last month, itself took two years to complete.
Mr Khaw said the CRL, which is expected to be ready by 2030, will "significantly enhance" the MRT network's resilience, and its capacity and usage will far exceed that of the existing North-East Line.
He also said the longer 9km skirt around the CCNR will incur an extra travel time of six minutes, compared with the more direct 4km route running underneath the reserve.
Alluding to high public expectations of the MRT, Mr Khaw quipped that in a minute's delay, a commuter could post 100 times on Twitter to "flame" the Land Transport Authority and the rail operator.
This extra six minutes could not just be "brushed aside", he said.
Mr Ng said the skirt-around alignment would serve more commuters, but Mr Khaw replied that residents in the area are already served by the Circle Line and the future Thomson-East Coast Line.
Mr Khaw also said a skirt-around alignment would need longer tunnels and ventilation facilities on the surface. This option would cost $2 billion more and could result in land acquisitions.
But for the direct alignment option, 2km will be deep below the CCNR at about 40m - or 12 storeys - below ground level, and there will be no structures built at the surface level, Mr Khaw said.
Mr Ng also asked for the total cost of the CRL project, and which houses and buildings will be acquired.
Mr Khaw replied that it was still too early to know these details, and a second phase of EIA, to look into the impact of construction and running of trains underneath the nature reserve, will be done.
He urged Singaporeans not to take a biased approach to the issue, noting that some comments on the first EIA have been "very toxic".
"Keep an open mind, go with the facts. Keep an open mind and look for the evidence," he said.
Parliament resumes today.
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