Circle Line of the Singapore MRT is the fourth mass rapid transit train line in Singapore. At time of writing (May 2010), only 16.5 km of the line has been opened, with 16 stations. When fully completed, it will have 31 stations spanning a distance of 35.7 km, and will become the longest fully automated metro line in the world. The Circle Line is colour coded orange.
The next stage of expansion for the Circle Line will eventually connect the either ends of the routes to "close the circle". This was first announced by the then Minister for Transport Lui Tuck Yew on 17 January 2013. this is a 4-kilometre extension to connect the Marina Bay MRT Station to the HarbourFront MRT Station. Three additional stages are to be added. The working names of the stations were announced on 29 October 2015, and they are the Keppel MRT Station, Cantonment MRT Station and Prince Edward Road MRT Station.