In the 1980s, the SLE was proposed to link BKE in Kranji to the CTE in Yio Chu Kang.

[1] In 1983, it was announced that SLE would only be built after work on the northern expansion of CTE from Toa Payoh to Yio Chu Kang was completed.

The first phase of the construction of SLE consisted of a stretch between Yio Chu Kang and Upper Thomson Road, which included a direct connection with the CTE at Yio Chu Kang Flyover, and was opened on 24 March 1990.

The Upper Thomson Road - BKE extension was opened in two parts: from BKE to Woodlands Avenue 2 on 5 November 1995, and from Woodlands Avenue 2 to Upper Thomson Road on 22 February 1998.

The third stage of construction, completing in July 1996 from Woodlands Avenue 2 to Lorong Gambas.