> where I wondered when will personal (flying) quadcopter vehicles have more annual passenger miles than every passenger rail combined (subways/light rail/Amtrak) in the U.S.?

I had a similar thought a few days ago in respect of Waymos specifically: "Americans take about 34 million public-transit trips a day. Assuming 25 rides per day, that's about 1.4 million self-driving cars to rival public transport's impact. Waymo has "about 3,000 robotaxis deployed nationwide." Doubling fleet size annually–Waymos and non-Waymos, though currently they have no peers–would get us to parity in less than 10 years. (A more-realistic 35% growth rate puts us around 20 years.)"

https://news.ycombinator.com/item?id=47915937