Comment by djankauskas
16 hours ago
Yes they are, those balises on tracks are the standard technique for both metro and mainline signaling systems at this point. Those balises, often combined with radio communication, are how fully autonomous trains have been operating for decades. (It's possible to use things other than balises, like track radio loops as in LZB or more recently beacons or LIDAR, but balises are standard and pretty affordable).
Yeah, that works and has been for a while. I was talking about non-track based safety systems. You can have balises in specific locations, but you can't have them every few centimeters on your whole network.
Why would you need that many? Trains can keep pretty reasonable track of the distance between two balises using odometers.
There are also other solutions, e.g. LZB uses a phase change of the signal every 100 meters as an additional precision signal.
Because balises cost money, are payed for by infrastructure companies. Their position needs to be decided a priori, so you can't have the whole resolution on the whole network in order to get as close to the physical limits between trains as possible. Also it would be nice to be able to implement automatic shunting without additional infrastructure costs.
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I guess I'm confused by why non track -based solutions are necessary? ETCS L2 would gracefully handle a system restart and automatically force a 40kph speed limit until a train traversed the unknown track proving no occupancy, and allowing proceeding trains to go faster. This all works on a track-based system.
Because railway infrastucture companies would like to not pay for them, not build more tracks and still get more capacity due to "digitization".
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