Half-height platform screen doors

The half-height platform screen doors had been installed to prevent track intrusions. Some of the Overground stations do have half-height platform gates:
 * Alexandra (3 Jul 2011)
 * Lower Delta (30 Sep 2011)
 * Bukit Timah (30 Sep 2011)
 * Kranji (13 Oct 2011)
 * Woodlands Checkpoint (13 Oct 2011)
 * Mandai (13 Oct 2011)