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A noticed at few sites on this line (near Ashford, Feltham, Virginia Water) recently where pieces of new kit are appearing bedside the track. Seems to mostly be near the station and was wondering what they where?

Related to the platform extensions?

I really ought to know the answer to this, but I don't. I suspect though, like you, that it's related to delivering the "ten-car railway", HLOS platform extensions.

Could they be the trackside balises for the new SDO equipment?

Possible, but my understanding is that the automatic SDO (ASDO) kit is only being installed at stations where (a) the existing platform is less than ten cars AND (b) it's not practicable to extend the platform to a ten-car length. I can't remember the platform lengths off the top of my head, but Feltham *may* be one of these locations if the platform isn't ten cars already, given that it's restricted by a bridge at the London and and the level crossing at the country end. I can't remember what the status of the platform lengths/extensions is at Ashford or Virginia Water.

I was under the impression it would be installed at all stations because the system will work by releasing doors to be opened when a carriage runs past the balise. Will the system be configured differently for full length stations to just release all doors as standard, and will that require some sort of GPS so the train knows it's at a full length station.

One of the recent CP4 updates explains that they are being fitted (in phases) to cover almost all SWT stations, although the initial installation is on the Windsor side 10 car project.  I was told by a guard manager a year or so back that ASDO will definitely cover all the stations where EMUs operate, which will inter alia overcome problem stations like Shawford and Beaulieu Rd, where local door only access is the norm on 444s.

ASDO will also allow for increased safety if for instance a train stops slightly off the platform even if it is otherwise the right length, eg a 12 car stopping a car too soon on a 12 car platform accidentally...

PS - checked the CP4 info, it's down as 168 stations, and also the entire Desiro fleet, as well as the obvious 458/5s.

I believe the system was trialled on some 450s towards the tail end of last year, there were some services with reduced carriages for a couple of weeks to allow the trial.

Yes, that trial rings a bell too.

Doing a bit more digging, it seems they are using the Hima Sella Tracklink III system, which seems to use passive RFID beacons only, ie non-GPS.  Southern's system is the second generation variant which uses both GPS and inductive loop balises/beacons, but in this case the trackside gear needs a power supply.

Apparently the same 3rd gen system is used on the latest LU installations, and the beacon/balise is relatively small, (only a few inches long) so I would now be tending to doubt it results in visible infrastructure changes.

Paul

Following up this stuff about ASDO balises for SWT, following trials the physical device to be used has been 'beefed up' a bit, and now consists of a yellow bar across the length of a sleeper between the tracks, held by the track clips (in a similar manner to the way TPWS grids are secured).

It is an entirely passive device, examples are now fitted at the end of P4/5/6 at Reading, so if anyone is going past they'll see them easily.

Paul