I'm not sure what you're purporting to show other than two people disagreeing with each other, without providing evidence... Sure, an individual subway car has "more capacity," but does a subway system have more capacity? For example, I rarely see BART trains come within five minutes of each other. A tunnel that allows cars within 10 seconds of each other could provide more capacity than a tunnel with higher-density trains spaced further apart. Average density across the tunnel system could be higher (aka more throughout) with autonomous vehicles even if individual transport units have lower density (SUVs instead of train cars).
Off the top of my head, here are issues train cars face with managing density that autonomous vehicles wouldn't face:
1. Needing to stop at stations where few people are getting on or off, meaning that trains behind you must be at least (MAX_SPEED * STOP_TIME) behind you. With cheap tunnel boring + AVs, you can quickly and cheaply build tunnel branches that skip exits, so individual cars need less space between them (you branch off to exit; no need for extra rails or switching technology, since it's built into the cars).
2. Entrance/exit from the train car: with trains, any jerk can run in as the doors are closing, preventing the train from leaving, backing up the trains behind you and leaving a huge gap with trains in front of you. With AVs, you're already in the car.
3. Trains have fairly long stopping distances, increasing the distance needed between trains for safe operation. Some quick Googling indicated that an 8-car passenger train traveling at 80mph can take over a mile to come to a complete stop — it's hard to imagine a car with such long braking distances. That puts a pretty hard lower bound on how densely you can pack an ordinary subway tunnel.
Maybe I'm totally wrong, but it would be more useful to give actual data and evidence than knee-jerk shutdowns. It's not obvious to me, a non-train-engineer (like many on this site!), that the dismissive tweet is particularly meaningful.
Off the top of my head, here are issues train cars face with managing density that autonomous vehicles wouldn't face:
1. Needing to stop at stations where few people are getting on or off, meaning that trains behind you must be at least (MAX_SPEED * STOP_TIME) behind you. With cheap tunnel boring + AVs, you can quickly and cheaply build tunnel branches that skip exits, so individual cars need less space between them (you branch off to exit; no need for extra rails or switching technology, since it's built into the cars).
2. Entrance/exit from the train car: with trains, any jerk can run in as the doors are closing, preventing the train from leaving, backing up the trains behind you and leaving a huge gap with trains in front of you. With AVs, you're already in the car.
3. Trains have fairly long stopping distances, increasing the distance needed between trains for safe operation. Some quick Googling indicated that an 8-car passenger train traveling at 80mph can take over a mile to come to a complete stop — it's hard to imagine a car with such long braking distances. That puts a pretty hard lower bound on how densely you can pack an ordinary subway tunnel.
Maybe I'm totally wrong, but it would be more useful to give actual data and evidence than knee-jerk shutdowns. It's not obvious to me, a non-train-engineer (like many on this site!), that the dismissive tweet is particularly meaningful.