Why self-driving trains are much easier to implement, yet there are not that many systems capable of doing that?
Many newer metro lines are GoA 2 or 3, theoretically capable of running autonomously, but they always require a driver in the loop.
My partial answer is, making an extremely reliable system is hard. If someone wrote a deadly bug even only happen at a very corner case, it still can kill people. And it's quite hard to prove there isn't such bugs.
We don’t half self driving trains because there’s far, far less incentive.
You only need 1 or 2 drivers for a huge train carrying a lot of ppl/stuff. Optimizing away the driving barely reduces the cost of operating the train as a whole.
With cars, everyone drives themselves. There’s a lot more driving happening and so if you can automate that away, you create more value.
My partial answer is, making an extremely reliable system is hard. If someone wrote a deadly bug even only happen at a very corner case, it still can kill people. And it's quite hard to prove there isn't such bugs.