QUESTION:
Is current technology mass transit by rail limited by train velocity?
ANSWER:
No.
The limiting factors for the installation, adoption and use of mass rail transit, are, imo:
1) Ticket Cost
2) Infrastructure build and maintainance costs
3) Availability of land for use by said rail network (At least in the UK, where i live)
Is that true, though? Do you have supporting studies or documentation? I'm not calling you out - rather I think we all have our own opinions that often aren't reality. Me included regarding trains.
I can tell you that in the Boston to NYC corridor, Amtrak implemented the Acela high speed rail and over the years, it has slowly gobbled up market share from the airlines to the point that it now has something like 70%. I have driven, flown, taken the bus and taken the train between the two cities and the high speed train is a really nice experience that I used to discount until I tried it. The only downside is that it isn't faster. That is the aspect they are working on. They aren't working on making ticket prices cheaper. Nor are they trying to lower maintenance costs. Nor are they worrying about availability of land. They have existing rail lines in densely populated areas (the only places where rail works), and the problem is upgrading old tracks, bridges, transfer points and tunnels to handle higher and higher speed trains. The trains they use here could go quite a bit faster, but they lean into turns, and this makes them incompatible with many of the tunnels. They are working on upgrading the bottlenecks one-by-one so that they can increase the speed of the trains, and they have already committed to buying a newer batch of trains which will be faster still. So my anecdotal evidence is that it's all about speed - people are perfectly happy to pay the same price as a plane ticket in order to be able to show up 10 minutes before departure, sit in a comfy chair at a table, get WiFi internet, have a meal car with food and drink and arrive at Penn Station on a perfectly predictable schedule. The straw that broke the camels (airlines) back was going from regular speed rail to high speed rail - that stole tons of airline market share. Making it faster still will grab even more.
So the Hyperloop, assuming it can be made to work on a practical, day to day level, solves exactly none of those issues.
Issues which, IMO, are not issues.
Hence, Hyperloop = pointless, irrelevant of any engineering practicalities or solutions.
I think people would absolutely pay a pretty penny to get between major population centers quickly. A 30 minute express hyperloop from Boston to NYC could easily command $200 each-way ticket prices all day long. That's around a 150 mile trip each way.
Sure, there are engineering challenges, but no way is it as much of a slam-dunk in the outrageous category as batterizer, solar roadways, the ultrasonic power thing or the other stuff Dave and Thunderfoot are comparing it to, IMO.