Existence is an important first step. I'd argue it's still at least five years away from replacing my daily commute, though.

So, were the train experiments successful? If so, what is stopping it from replacing regular trains?

From a distance, trains should be simpler: it's just a horizontal elevator. So why are there still mostly regular trains? I think answering that will likely help explain why self-driving cars won't be a thing in at least another 10-20 years.