The project comprised two 15 km-long, 2-4 lane concentric ring tunnels around the central business district, with 8 interchanges and 33 entrances and exits.
The project was first considered in the 1980s and was seen as a way to cater for increasing traffic growth in and out of the city centre.
On 29 August 2017, the Land Transport Authority (LTA) scrapped this project as part of a shift to a car-lite society.
This comes after enhancements to the Mass Rapid Transit (MRT) network and changes to land use policies over the years since the project's conceptualisation.
As a result, land safeguarded for the project since 1993 was freed up for other developmental purposes, allowing for greater flexibility by developers.