Yes, but as long as the central signalling system is working, it already knows where the train is, with no need to involve GPS. (And where modern signalling and train protection systems need increased precision as compared to the granularity of track circuits/axle counter sections, the solution usually involves a combination of on-train odometry plus track balises at occasional intervals in order to reset any inaccuracies that might have accumulated.)

What we're talking about here is some sort of TCAS-equivalent for the case where the central signalling is down – while it's easy to accurately localise trains with the aid of a central signalling system that authoritatively knows about the infrastructure layout, it's quite more difficult when you're trying to do the same thing in a decentralised, train-local fashion.

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1718627440 an hour ago | parent [-]

Yep, that's what I was trying to convey as well. There also seems to be RCAS, but it sounds like a newly invented system. https://www.dlr.de/en/kn/research-transfer/projects/next-gen...

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iggldiggl an hour ago | parent [-]

And as of now, I suppose that RCAS (or RCAS-like systems) is best suited for (especially minor) single track branch lines that don't currently have a full-scale signalling system already up-and-running, but instead still rely on "Timetable & Train Order" and similar systems.

Single track means that at least outside of stations, collisions can be reliably identified without much danger of false positives (and for station areas you can just institute a blanket speed limit to compensate for the gap in RCAS coverage, which might not even be any lower than the speed limit required for traversing diverging/spring-operated/hand-operated points there anyway), and no already existing full-scale signalling system means that RCAS actually provides a significant safety benefit and is therefore likely worthwhile from a cost-benefit-analysis point of view, too, if you're actually regularly operating multiple trains simultaneously on that kind of infrastructure.

Whereas on multi-track mainline railways avoiding false positives is much harder and normally you should already have proper signalling and train protection systems in place anyway, so the additional safety benefits of RCAS would be much more marginal.

	▲	ricardobeat 36 minutes ago \| parent [-]
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