Constructed and opened as part of the North South line (NSL) in the early stages of development, the East West line is formed after the opening of the eastern extension to Tanah Merah in 1989. Nevertheless, till today, both lines used identical signalling equipment and rolling stock. The East West Line signalling systems have been upgraded along with the North South Line and is the second line to have its signalling upgraded completely, converting it from semi-automatic to fully automated operations.