Greentext

The problem with 'The Line' is that travelling 170KM in 15 minutes requires an average speed of 680KM/h (I wrote out why that's insane lunacy from an engineering perspective, but I shoved it in a footnote), but you can achieve a 15-minute city of the same volume just by having an, IIRC, 13KM square with 100m-high buildings (and building 100m-high buildings is waaaay cheaper than building 500m-high buildings), built on a simple grid of normal 100KM/h trains - the Manhattan Distance of the maximum distance in a 13KM square is 26KM, which to be fair is still 36 seconds over the 15min mark even if your average speed is 100KM, but 1) it almost achieves the exact same thing as the trillion-dollar sci-fi tech, and 2) if you really care about the sharp 15-minute city premise then you can bump your trains up to run at 150KM/h (which is perfectly doable and only a little more expensive).

Anyway, point is that the only way The Line can fulfil its promises is by casually dropping a trillion dollars on a problem that may or may not be solvable, and will almost certainly be an order of magnitude or three more expensive than the bog-standard existing solution. A 680KM/h train is fucking expensive and while yes, it might be physically possible, most people want the cost of their commute to be lower than their daily wage earned from the job they commute to.

If The Line was ever built (and was cheap without subsidies somehow and became populated), then the first thing to happen after its populated would be a ton of building sideways, mostly around the midpoint/centre of The Line. Why? Because that's the prime land that's empty and therefore cheapest to build on, that's closest to everything (the midpoint of The Line should be ~7.5mins away from everything at most, and would also be the most accessible spot in the city and therefore have the most desirable business locations). And new buildings would be built around there, not at the ends of The Line. They'd add extensions to the train line that turn 90 degrees out, so that people further away from The Line could access the train system. This all would continue until The Line became The Circle.

The only way The Line stays a line is with economic antigravity. Metaphorical antigravity, to be clear. Not the sci-fi tech.,

Never going to happen in america

...why? I'm not saying it'll be easy, but half the time I see that line it's used as a justification for why people shouldn't demand it happen. And frankly, "never" is too strong of a word.

680KM/h isn't even possible with a normal maglev, you'd need to either shove the maglev in a vacuum tube or build a rocket train or something equally insane just to have a maximum speed of 680KM/h. But you actually need a higher speed than 680KM/h since you start out at 0KM/h and 680KM/h is just the average - and since your acceleration is limited to speeds that won't kill the passenger, you really do have to factor it in, one way or another. See, your train has to either permit passengers to stand (which sharply limits safe acceleration without someone being knocked over and bashing their head open on a rail) or it has to give everyone time to board and then seat (all of which takes time for boarding), and you also need a way to ensure that random dickheads won't ignore the rules and stay standing. A boarding delay will kill your average speed just as much as low acceleration.