Comment by amiga386

They do, in an extremely expensive system called ETCS, which everybody is aiming for but it takes a huge pile of money and years of work to ever get there. Which is why a huge portion of rail networks don't (yet) use it.

The issue is not the idea, it's that railway signalling systems have to be an interoperable, multi-vendor, tested and accredited pile of little ideas like this, that have infinite numbers of ways to go wrong and have corner cases by the metric ton. And it's not like coding a website, where you can just ignore standards and focus on your case. "Your" rails need to support other people's trains. "Your" trains need to run on other people's rails. Even in a fully closed system with your trains on your rails... who's going to be your equipment maintainer and supplier for the next 30-50 years of their operational life?

Read this article and notice how often cost and project overruns are mentioned:

https://www.railengineer.co.uk/etcs-preparing-the-east-coast...

> The use of ETCS is driven by deliverables, not the technology but concerns exist as to why it is costing so much. In Europe, the success of ETCS is driven by country mandate and a system authority which helps to create a stable ongoing work plan.

> There is also the question of strategic safety versus functional safety, namely fundamental versus site specific. Over-specified ETCS undermines the strategic safety and functional over scope and so drives unaffordability since the accreditation inflates the cost.

> Cost must be driven out of ETCS if it is to be the preferred system for ongoing renewals. Despite interoperability requirements, there is risk in always using the same supplier. There is no common way of delivering ETCS. Having it as an overlay system will always be expensive and not beneficial to the business case. Lessons have been learned from the application of ETCS to the Cambrian route, the Thameslink central core, and the Northern City line from Finsbury Park to Moorgate but all of these have only one type of rolling stock in day-to-day operation. Equipping a mixed traffic railway as in the ECML makes it much more difficult.