It will run in an east–west direction from Changi to Jurong Industrial Estate via Loyang, Pasir Ris, Hougang, Serangoon North, Ang Mo Kio, Sin Ming, Bukit Timah, Clementi and West Coast.

Nevertheless, the Government ultimately decided after years of assessments and deliberation to continue with the original direct route in 2019, citing commuting time and economic factors as well as long-term energy consumption.

[4] The proposed full line is expected to have a daily ridership of over one million in the long term,[5] and to cost an estimated S$40.7 billion.

[11] On 19 July 2013, the NSS put forward two proposed alternative alignments:[12] 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, and a southern route skirting the reserve along Lornie Road.

One engineering professor Lee Der-Horng noted the possible feasibility of constructing the line through the reserve without impacting the environment, though he said the decision "shouldn't be just based on transport".

The EIA was to be conducted in two phases with the first 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.

[21][22][23] The Punggol Extension was initially conceived as part of the North Shore line,[24] which was first announced by National Development Minister Lim Hng Kiang in December 1996.

[30][31] However, the restrictions imposed on construction works due to the COVID-19 pandemic have led to delays and the completion dates for CRL1 and CRLe were pushed by one year to 2030 and 2032 respectively.

[36] In December 2021, as part of a virtual exhibition by the LTA, a future system map depicted a series of 11 unnamed stations on the western half of the CRL.

[39] Based on tender documents, The Straits Times projected in February 2022 that civil works for the CRL might be completed by end-2033, with operations beginning in 2034 or later.

[46] The 58 kilometres (36 mi)-long CRL is planned to run in a generally east–west direction, serving 27 stations[41] and being an alternative route to the existing East–West (EWL) and Downtown (DTL) lines.

The line branches off to Punggol Digital District[30] and goes south-west towards Tampines North, and west to Hougang, and further towards Sin Ming via Ang Mo Kio.

[47] Phase 2 of the line connects Bukit Timah to Sin Ming, tunneling through the CCNR, before continuing south-west to West Coast via Clementi, before heading north-west to Jurong Lake District.

[51] However, then Transport Minister Khaw announced in 2018 that express services were considered not feasible, citing the higher cost needed to build extra tracks and additional signalling systems that can affect non-express commuters and existing lines.

[86] A CRL Train Mixed Reality Mock-up was displayed at LTA's Hampshire office as a public engagement exercise.