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I suspect it would be hard to distinguish the green between the yellows at distance. Also harder in circuitry and monkeys with the aspects for the normal trains more. Also couldn’t have been deployed to a 3 aspect area, where flashing green can.
One step further in flashing aspects rather than mixed colours is two different flash cadences. This is done in other countries.
In that Czech signalling sequence I posted, both greens and yellows have two different cadences denoted by the different 'star bursts' in the middle sequences.
Generally, fast-er or slow-er cadences may be differentiated at distance and obviate mixed colour aspect potential difficulties.
That we (GB) do not currently do it here is not a reason to not do it, it just requires a change in attitude. If, only one suggestion, if we had 155 mph (and that was a BR APT goal) on conventional signalling (even if relayed to cab), then if the ECML tested flashing green was for 140 mph, there is no reason why WCML APT 155 mph could not have had flashing green at a different cadence on top of it. The circuitry is not /that/ complex.
If the green failed, it would show double-yellow which would be more restrictive than necessary for conventional trains. And even if the green were working, the yellows would mean it would have to be accompanied by an AWS warning, which again would be unnecessarily restrictive for conventional trains.
== Doublepost prevention - post automatically merged: ==
One step further in flashing aspects rather than mixed colours is two different flash cadences. This is done in other countries.
In that Czech signalling sequence I posted, both greens and yellows have two different cadences denoted by the different 'star bursts' in the middle sequences.
Generally, fast-er or slow-er cadences may be differentiated at distance and obviate mixed colour aspect potential difficulties.
That we (GB) do not currently do it here is not a reason to not do it, it just requires a change in attitude. If, only one suggestion, if we had 155 mph (and that was a BR APT goal) on conventional signalling (even if relayed to cab), then if the ECML tested flashing green was for 140 mph, there is no reason why WCML APT 155 mph could not have had flashing green at a different cadence on top of it. The circuitry is not /that/ complex.
By different cadence do you mean the rate at which the aspects flash? Or do you mean that two aspects flash differently? In the UK, the two yellows of a flashing double-yellow aspect flash in synchronism, but it would be possible to have aspects that flash alternately (like the twin red road lights at a level crossing).
The circuitry might not be that complex, but I suspect that the difficulty would be getting a type-approved flasher to do the job, especially if only a very small number are required for a trial installation such as the flashing greens. The flashing green installation was able to use the flasher already type-approved for flashing yellows. This flasher incorporates built-in lamp-proving that holds up during the dark phases, as well as proving that the flasher itself is working.
I did some development work for using British SSI to control North American type signals with their variously coloured flashing aspects. It wasn't as simple as we initially hoped - all sorts of problems arose, particularly with lamp-proving and fault monitoring.
If the green failed, it would show double-yellow which would be more restrictive than necessary for conventional trains. And even if the green were working, the yellows would mean it would have to be accompanied by an AWS warning, which again would be unnecessarily restrictive for conventional trains.
== Doublepost prevention - post automatically merged: ==
By different cadence do you mean the rate at which the aspects flash?
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