3 ms·
One of the rare benefits of the antiquated signalling system in the UK, using good old-fashioned analogue tech, lots of wires and relays. I was once shown a bug
by jsingleton 10y ago
One of the rare benefits of the antiquated signalling system in the UK, using good old-fashioned analogue tech, lots of wires and relays. I was once shown a bug in the system, that was literally a bug, squashed between two relay contacts.
- IshKebab 10y agoVery rare. It seems like 90% of delays are due to "signalling problems" (which is probably also code for "we have no idea what is going on", but still...)
- jsingleton 10y agoThe signals are designed to fail safe, due to gravity. But because they are electromechanical they fail a lot more often than solid state digital tech.
- gsnedders 10y agoGravity doesn't play into it much any more; semaphore signals are increasingly rare by this point, certainly on any main line. Modern electric signals simply default to danger in the absence of contact to the signal box, and fail-safe behaviour is maintained by the rule book stating that a signal displaying no aspect is equivalent to a signal displaying danger.
- jsingleton 10y agoGravity is still very important. The way that electric signals fail safe is that the relay is mounted in such a way that if something fails then gravity pulls the contacts to the danger position.
- lewiseason 10y agoAren't relays usually lightly spring-loaded/tend towards the NC position irrespective of which way you mount them? Maybe railway signalling relays are different, but none of the relays I've ever seen leave that behaviour to gravity.
- gsnedders 10y agoNotably, the UK still largely relies upon track circuits for train detection, though the GWML (from London Paddington to Bristol) is moving to axle counters along with its move to ETCS Level 2. It's likely the rest of the UK will slowly move over to axle counters as signalling equipment becomes life-expired.