Cross Island MRT line

Since its announcement on 17 January 2013, there has been a controversy over the alignment of the line's Bukit Timah stretch as it appears to cut through part of the Central Catchment Nature Reserve (CCNR) and MacRitchie Reservoir, hence prompting the Nature Society Singapore to call for a change in the alignment, although the Land Transport Authority insisted that the alignment was not finalised as soil investigations and feasibility studies have yet to be conducted. An Environmental Impact Assessment (EIA) was commissioned to study the impact the line would have on the natural habitats of the reserve. Various stakeholders, including nature and environmental groups, were engaged and consulted to ensure that their views and concerns are accommodated as part of the Environmental Impact Assessment.

On 19 July 2013, the NSS has put forward, in a position paper, two proposed alternative alignments for this stretch of the Cross Island line. The LTA claims that none of the trees or plants (vegetation) above the ground will be affected.[13]

The proposed alignments include a northern route that would run close to the Thomson–East Coast line, heading west towards Mandai, Sungei Kadut and Gali Batu before terminating at Choa Chu Kang, which will be an interchange to the North South line, Bukit Panjang LRT and the upcoming Jurong Region line. The other route will run along Lornie Road and was cited to "add 1.7 kilometres to 2 kilometres to the Cross Island line, and an estimated four minutes' additional travel time. It would present an opportunity to serve residents near Adam Road and visitors to the MacRitchie Reservoir Park", running almost parallel to the stretch of the Circle line from Marymount to Botanic Gardens. However, engineers noted that "it may still be possible to construct the tunnels along the original proposed route without disturbing the nature reserve, but this must be examined in detail" and that a "straight rail line is better and cheaper from the engineering and operations point of view".[14]

On 24 February 2014, the LTA called for a tender to assess the environmental impact of the line, targeted for completion by 2016. The study will help to facilitate the subsequent civil works for the line.[15]

On 3 July 2014, LTA appointed Environmental Resources Management (S) Pte Ltd (ERM) to conduct the EIA for the section of the line around and through the nature reserve. The work started immediately and was targeted to complete in 2016. The works will include studying the ecosystem and physical conditions along both the straight and skirting alignments, as well as assessing how construction and operation of the line would affect the CCNR.[16]

On 19 October 2017, the soil tests for determining the Cross Island line's alignment along the CCNR were announced to be nearing completion. The soil tests will help engineers determine the soil and rock profile under Singapore's largest nature reserve, started in February and have been watched closely, especially by environmental groups who urged the Government not to build the MRT line under the CCNR. "The works are expected to be completed by the end of this year," said the LTA.[17]

On 20 March 2018, the LTA declared that the release of the findings on the environmental impact of drilling and other initial works that have been done to assess if the Cross Island line can be built under the CCNR would be completed later that year. The investigation works, which were completed in 2017, will help in the final decision on the alignment of the line. The findings were released to the public.[18]

The Ministry of Transport announced on 4 December 2019 that the direct route underneath the CCNR had been chosen. The construction cost is expected to be lower by $2 billion by taking the direct route, and the Ministry also said the direct route would be better for the environment in the long run as it will have lower energy consumption.[19]