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We've been told on our NR briefing days that in future there will be a move away from track circuits towards axle counters on high speed lines, due to the signal sections being so long.
I've had personal experience of unreliable track circuits. Coming happily out of a cutting at 90 mph after travelling for over twenty miles on greens, the next signal which controlled a junction was red. There was no way I could stop in time, so that was a category B SPAD on my licence for evermore. But it was a relief at the time just to know that this was a system fault and that there wasn't a train making a conflicting move towards me as I'd feared.
An investigation into the signal 'going back' on me gave the reason as damp ballast in the signal section in advance.
I've often wondered about whether it would be possible to use digital signals to indicate the prescence of a train in section instead of having to tweak analogue circuits all the time.
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