20-05-2011, 04:47 PM
Take 1
I seem to recall reading, but wasn't around at the time that:
Semaphore signalling always used an overlap of 1/4 mile.
This figure was derived by experiment, but was ultimately an arbitrary figure.
Once this arbitrary figure got written down as being a "standard", anyone who suggested using a distance even a yard less than the written down figure was crucifed as a heretic
When 2, 3 and 4 aspect colour signalling came along, an interim arrangement was that 2 aspect used a 400 yard overlap, 3 aspect used a 300 yard overlap, and 4 aspect a 200 yard overlap, the thinking being that in the latter cases, the driver is given more frequent updates about the state of the line ahead, and so the likely scale of an error will be reduced.
- hence it could have been said that the heretically short 200 yard overlap of 4 aspect signalling was a compromise of signalling principles to meet operational needs.
Take 2
Signal engineers often tend to think that we're so important that we are self justifying, and those trains are just an inconvenience.
Let's just remember that if there weren't any customers, there would be neither trains nor signal engineers.
so lets's amend the statement;
"Restrictive Signals, overlaps and inflexible signalling are all examples of the commercial train service delivery being compromised by fixed signalling rules"
Let's see who gets annoyed by the above statement!
I seem to recall reading, but wasn't around at the time that:
Semaphore signalling always used an overlap of 1/4 mile.
This figure was derived by experiment, but was ultimately an arbitrary figure.
Once this arbitrary figure got written down as being a "standard", anyone who suggested using a distance even a yard less than the written down figure was crucifed as a heretic
When 2, 3 and 4 aspect colour signalling came along, an interim arrangement was that 2 aspect used a 400 yard overlap, 3 aspect used a 300 yard overlap, and 4 aspect a 200 yard overlap, the thinking being that in the latter cases, the driver is given more frequent updates about the state of the line ahead, and so the likely scale of an error will be reduced.
- hence it could have been said that the heretically short 200 yard overlap of 4 aspect signalling was a compromise of signalling principles to meet operational needs.
Take 2
Signal engineers often tend to think that we're so important that we are self justifying, and those trains are just an inconvenience.
Let's just remember that if there weren't any customers, there would be neither trains nor signal engineers.
so lets's amend the statement;
"Restrictive Signals, overlaps and inflexible signalling are all examples of the commercial train service delivery being compromised by fixed signalling rules"
Let's see who gets annoyed by the above statement!