That is the common solution to have high speed and low speed trains use the same track but that wasn't my point.
My point is that people are inclined to demand high speed trains stop at everyone's doorstep and don't see that that slows the train down to snail speed.
idea of having 350kph+ trains that do not stop but having train cars that accelerate and decelerate passengers to train speed.
you have two tracks side-by-side. one for a 350kph high speed train on a 1000km loop the express, and the other trains that run on a side catch up track, the shuttles. so the system has 4 train tracks, 2 running in one direction, two running in the other direction.
two are shuttle tracks. and two are express tracks.
when the catch up shuttle train is side-by-side with the high speed express train,
then the passengers can transfer from train to train via a side door way at
with the high speed express trains that never stops at any station!
the transfer shuttle train accelerate from the stations so passengers can catch up with the 350kph high speed express trains.
and then decelerate so other passengers can transfer to stations. also the catch up transfer train can hop between stations.
this would only work in China, because of the massive infrastructure needed for 4 parallel 350kph train tracks
the passengers would need to transfer via a elevator type doorway at the train stations.
not a open platform because of the express trains passing behind the stopped transfer shuttle trains.
this all sounds complicated and it is. passengers would need to transfer via doorway at the train stations.
then transfer via doorway at speed to the express train.
so the design of the shuttle railcar is not the same as the design of the express railcar.
the shuttle railcar has a telescopic transfer door that docks with the express railcars at 350kph +
also the shuttle railcar has a door that docks with the train station doorways, in its opposite side. go figure this one out.