I mean it doesn't scale in the slightest so it doesn't solve any problems really, so there's that. In terms of latency it depends, every decent underground system will have passengers waiting no more than a few minutes. Worst I saw was in Naples where I waited over 15 minutes. 15 was too long, but I'd rather wait a few (<10) minutes to ride a train than wait some amount of time less to ride a Tesla. In fact, I would wait just to avoid riding a Tesla at this point.