This is hilariously hand-wavey of the complexity and strikes at my frustrations between how most IT engineers see the world vs how real-world engineers do.

There are parallel tracks within metres of one another. Switching yards have tonnes of them and require precise knowledge of what’s in what.

GPS isn’t SIL.

Trains operate in cluttered environments with reflection and echo abound. That causes drift above the separation of tracks.

There’s way more than “a few” dead spots, and what happens if those repeaters fall over?

There’s tonnes of reasons why high tech isn’t used in train safety-critical systems. The fact you suggest an arduino as an appropriate platform for this is frankly absurd and underscores your misunderstanding of the whole issue.

Close enough isn’t good enough. Crashing doesn’t just mean you reboot or reload the program and try again. It means people die.

Edit to add: A good rule of thumb I’ve learnt after 15 years in the game: if you look at the solution to an engineering problem and then start a sentence with “why don’t they just…”, you probably don’t understand the problem well enough.