Why do MRTs have an extra set of tracks in between the ones used? (via Stomp)

Thank you for your enquiry.

According to the Wikipedia entry on Mass Rapid Transit, the "Ang Mo Kio, Jurong East and Tanah Merah stations were built with a third middle track for off-service trains to stop at before they return to their depots, but the last two are now used as termini for the North South Line and the Changi shuttle, respectively." (source: http://en.wikipedia.org/wiki/Mass_Rapid_Transit_(Singapore) ) , last accessed 03 Sept '07.

In addition, according to SMRT, the stations with three tracks are interchange stations. For example, Jurong East station has three tracks - one heading towards the north (Marina Bay via Woodlands), one to the east (Pasir Ris) and one to the west (Boon Lay). For the Ang Mo Kio station, it acts as a holding stop for trains which are faulty and hence withdrawn to the Ang Mo Kio train depot.

You may also wish to contact SMRT via their general enquiries hotline 1800-3368 900 for further clarification.

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