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Last night while waiting for the train at South Yarra station in Melbourne, I saw these reflective triangles stuck on the sides of the train track rails. They were evenly spaced a few metres apart for as far as I could see down both ways of the tracks. They could only be seen on the far pair of tracks, and the tracks on the other side of the platform also had these little triangles on the far pair of tracks. I'm assuming that there are also triangles on the near pair, but stuck on the other side of the rails where I couldn't see them.

There is a picture of the platforms and tracks on the Wikipedia article for South Yarra Station from 2014 which shows they weren't present then.

I can't work out what these reflective triangles might be used for. What is their purpose?

Reflective triangles on train track rails

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They are markers used for accurate position monitoring, without the need to close the tracks to trains and allow people to work close to them. All the markers can be scanned from a few fixed points (e.g. on the platforms) to create an accurate 3D picture of any movement of the track.

For example the sleepers or ballast may have been replaced recently, or there might have been other civil engineering work nearby which could have disturbed the tracks.

Similar markers are sometimes used as a reference points for train drivers (for example when shunting) with illumination from lights on the train, but that is less likely within a station where the platforms are presumably lit anyway when the station is in use at night.

See https://www.berntsen.com/Surveying/Smart-Targets-Datums-Reflectors/RSAK80-Adapter-w-Smart-Angle-Targets, for example.

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  • $\begingroup$ Melbourne is undergoing a massive rail revitalisation project at the moment, including a new Metro style tunnel from just outside South Yarra station (maybe 200 metres away) to under the city. So there are indeed recent and ongoing rail works at and near South Yarra! $\endgroup$
    – CJ Dennis
    Oct 4, 2019 at 2:58
  • $\begingroup$ Tunneling may cause changes in ground level, which would be a good reason for the track monitoring. $\endgroup$
    – alephzero
    Oct 4, 2019 at 8:44

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