"double yellow"

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Chris
Beiträge: 175
Registriert: Donnerstag 24. Mai 2007, 03:26
Wohnort: Cardiff

"double yellow"

Beitrag von Chris »

In the UK system, where signal spacing is less than ideal for capacity reasons, signals are used that display 4 aspects instead of 3: danger -> caution -> advanced caution -> clear. This is done with a fourth yellow lamp above the green, which lights up with the existing yellow between red and green (from the bottom: RYGY).

Consider a series of BAHN "combined" signals, H0 H1 ..., and some additional BAHN "distant" signals. Assume line speed to be 120, and cautionary speeds to be 80 on double yellow, 40 on single. The "distant" function of H0 depends on H1, and of D0 on H2, etc.

What I have found is that if I place D0 immediately in advance of H0, where H2 is at danger the train proceeds at 80 imposed by D0. Where H1 is at danger, H0 is at caution and the train gets a limit of 40, only to then get a limit of 80 when it hits D0. If I were to place D0 in rear of H0, D0 would be ignored (as H0 will immediately impose either 120 or 40).

My immediate thought is that it could be possible if a train passing a second signal at caution with a higher limit retains the lower limit from the previous caution until it reaches a clear signal, in which case I could place D0 in rear of H0, and make D0 depend on H1 and H0 on H1|H2. This would also mean that single-to-double behaviour would work correctly, as D0 being clear would remove the 40 limit before H0 sets 80. This behaviour would generally make sense, as to most drivers around the world I imagine a caution means the same as it would in the UK - "expect to find a signal at danger", and that (without specific local instruction) a driver passing two signals showing the same cautionary aspect would not increase speed.

Are there any other horrid hacks that can be tried in the meantime?

TIA
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