It’s not computers, it’s remotely controlled from a central location. It’s interlocked with the signal system (the green/yellow/red lights) so a train is never signaled to go through switches the wrong way or at the wrong time. The switches are physically thrown either by big electric motors on a worm-drive, or with air. The air ones especially can snap over in less than a second. Be mortally afraid of the moving parts of switches, because they can throw with absolutely no notice, and injure you or worse, trap you so you can’t escape being run over by the train. Some rarely used switches are manual-throw. The train crew has to stop, manually throw them, move the train through ‘em, throw ‘em back, then the crewman must walk the whole train to get back to the engine. Often a trainmaster will drive out to throw the switches for them, to reduce delay.Some switches are also “sprung”… if the train is moving from the 2-track side to the 1-track side, he can run through the switch even if it’s not thrown his way. That would break normal switches. You asked about high speed… but on city streetcar lines, many switches are thrown by the motorman pulling past a trip-wire at a certain time. There’ll be a light, which points an arrow in one of two directions. One will light solid, then flash, then the other will light solid, then flash, etc. He waits until the arrow points the way he wants, then he pulls past the tripwire, and that throws the switch if needed.

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