A couple of notes;

if passenger train travel is already uncompetitive on price, faster train infrastructure is considerably more expensive relative to that. I am not sure whether that cost is fundamental or not -- maybe it's possible to find ways to build HSR infrastructure more-cheaply.

Fair, but it’s not like passenger rail is uncompetitive when taking everything into account. Cars are subsidised far more, and both cars and planes have far more negative externalities (i.e. real future costs) than trains. Plus, there’s a very real cost to being dependent on oil states for the bulk of our transportation options, one that has somewhat been demonstrated by the war in Ukraine.

I do agree on your point about high speed rail compared to normal rail, although I do think there is a lot of value in them being top of the line services to make rail as a whole more attractive.

Self-driving vehicles. Some of the objections I've seen to use of sleeper trains -- one way to mitigate the issues of trains being slower than planes is by having travel happen when asleep -- is people who dislike having shared sleeping environments. Maybe it's possible to do, oh, a self-driving car with a sleeper trailer or something like that.

Cars straight up suck and are less efficient than trains. Why you’d think of a car with a caravan but not, idk, private sleeping compartments in trains, is beyond me.

All traffic is expensive.

Germany alone subsidises it’s flight sector with billions of € by making kerosene tax free, there’s no VAT on international flights, etc.

The total direct cost of German road traffic to the public are estimated at 70 billion € per year, of which only 25 are being paid by people driving cars.

Well, 1960s had cars and people were using these for long distance travel due to the lack of other options. My dad, for example, drove his shitty car from Berlin to the south of Spain and back.

• I think the issue may be split in two - for some, the younger and poorer, cost is the limiting factor - they are willing to put up with longer travel times but cannot stem the additional financial burden. For older and more settled people (which I am transitioning to slowly) and my parents are in, comfort trumps price at all times. They will take the fastest, most direct route. They would fly even if it cost 2-3x more (which, for them, it does since they will take the premium airlines over budget).

• Going back to individual vehicles is, in my opinion, not a great solution. I am hopeful that we will find ways to have short distance air travel use more green options (electrical?) in the near-to-mid future, therefore eliminating the need to curb the undoubtably huge demand.