Put down your physics textbook and turn your civil engineering textbook to page 420.
I am talking acceleration - specifically, accelerating from a station, and decelerating as you arrive at a station. Those two activities create G-forces, and there is a maximum number of G's you can subject general passengers to, and when stations are close to each other - or the path between them isn't a straight shot - then your passenger G tolerance limits how high of a top speed you can reach before you have to start braking. Going faster requires your stations to be further apart, it requires the grade to be more gradual, and it requires the route to be more direct.
Subways stop every couple of blocks. It doesn't matter how big of an engine you put on a subway car, they will never go faster than they do now. Regional rail can be a little faster, but it still has to stop every couple of miles, which means even if you put a bullet train on those tracks it simply can't get up to speed. Rail between cities is pretty much the only place you can put HSR, and the currently-existing HSR track isn't a candidate for maglev track because it's not precise enough, straight enough, and in many cases long enough for a maglev train to get up to its top speed and actually save time over the HSR that already exists.
The way you avoid having high G-forces is by accelerating over a longer period of time. These kinds of trains would be used for fast transit between cities that are many hundreds of kilometres apart, not for short hops like a subway. This is precisely why China has different types of trains for different situations.
Put down your physics textbook and turn your civil engineering textbook to page 420.
I am talking acceleration - specifically, accelerating from a station, and decelerating as you arrive at a station. Those two activities create G-forces, and there is a maximum number of G's you can subject general passengers to, and when stations are close to each other - or the path between them isn't a straight shot - then your passenger G tolerance limits how high of a top speed you can reach before you have to start braking. Going faster requires your stations to be further apart, it requires the grade to be more gradual, and it requires the route to be more direct.
Subways stop every couple of blocks. It doesn't matter how big of an engine you put on a subway car, they will never go faster than they do now. Regional rail can be a little faster, but it still has to stop every couple of miles, which means even if you put a bullet train on those tracks it simply can't get up to speed. Rail between cities is pretty much the only place you can put HSR, and the currently-existing HSR track isn't a candidate for maglev track because it's not precise enough, straight enough, and in many cases long enough for a maglev train to get up to its top speed and actually save time over the HSR that already exists.
The way you avoid having high G-forces is by accelerating over a longer period of time. These kinds of trains would be used for fast transit between cities that are many hundreds of kilometres apart, not for short hops like a subway. This is precisely why China has different types of trains for different situations.