Northern Line TBTC Track Loops.

[Deleted]

On the newly installed Northern Line Transmission Based Train Control Signalling, why did they opt for the more traditional loops of cable on the tracks once more, rather than the modern radio based system employed on the Victoria Line Upgrade?
Was it something about radio based techniques being less reliable than the proven, tried and tested Track Cable Loop system?

[Deleted]

One of the requirements of the PPP Contracts was that any technology used should be proven in service. When Thales was chosen around 2003 by Tube Lines to resignal the Jubilee, Northern and Piccadilly lines their system was at the time already well proven for loops but not for radio. Hence the 'safe" decision. There's no particular reliability issue although of course the loop cable, which was supposed to be highly resistant to damage, has shown in use to be more susceptible to damage from track walks, replacement rails being dropped on it and lost traction shoes shearing the wires. However, broken loop cable does seem to be almost eliminated now though.

[crusty54]

I did ask why the cable wasn't being protected at a briefing meeting before the project started.

The reason I asked this was that the DLR had protected their cables after problems.

I was told it wasn't necessary.

[rincew1nd]

Posts discussing broken rails and track Circuits can now be found in this thread.