the problem with the "car-like-a-train" thing is that trains have really high capacity because their crossings are managed and they do not decouple/couple at high frequencies, but more importantly the people to space ratio is significantly higher, particularly since standees take up very little room. when you consider that cars need a whole engine for four seated people the general end result is that "cars-like-a-train" combines the worst of both worlds.
I don’t think the second part (about length of the train) is accurate at all. Yes, a train made of pods roughly car sized would be longer, but only roughly 3x. If you look at the duty cycle of say BART rail, you could fit a lot more than 3x trains on it. The rail is empty most of the time.
In a rail network you are only as good as your most congested pipe. BART is a pretty good example of this, because while the outer legs are relatively infrequent, they all converge on the Transbay tube at a combined 2.5 minute frequency, which is about the safe braking distance with some buffer for a train of that size and weight. Longer convoys would require even more braking distance, and already trains cannot rely on the AV technologies of cars because the braking distance is beyond line of sight.
You could run more trains only between the suburban branches but there isn't a whole lot of demand for that.
Coupling / decoupling at high frequencies would be a challenge for sure - but seems achievable in a world of fully autonomous vehicles that can communicate.
Right now to ensure absolute safety trains are mechanically coupled, which can't be done while moving, and takes a few minutes to do safely.
I believe most AV convoys propose virtual coupling to get around this, but the failure scenario where something in the convoy comes to a sudden stop and the other things in the convoy don't, is pretty gnarly. Modern trains have a bunch of mandated safety measures in their mechanical coupling to prevent nasty things like jackknifing, or even worse, telescoping https://en.wikipedia.org/wiki/Telescoping_(rail_cars)
This is speculation but I wonder if you could have cars couple with "cat whiskers" that are mechanical but not load bearing. so you don't need to rely on wireless comms for coordination
I’m not sure what load bearing means in this context.
Generally speaking mechanical coupling takes a while because you really, really do not want an errant car to detach during its journey. In the worst possible case scenario, a rear carriage has decoupled from a train and then the following one has crashed into said carriage. https://localtvkstu.wordpress.com/2013/11/05/crews-respond-t...
