How are railroad switches controlled?

Question

when a high speed train approaches a series of switch tracks, what opens the right switch?

Answer 1

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.

Answer 2

In modern cities of any size they are computer controlled.  Most of the big yards are computerized also.  You have to get to seldom used sections of the yard or cities that are really isolated to find switching that depends on manual switching.

Answer 3

On the Baltimore light rail system, the operator has to press a button to activate the switch.  The operator becomes involved when there is no computer control or if computer control is disabled or simply too risky to implement.

Some tracks in the Midwest have manual switches but they are going away one at a time.  All CSX switches go back to Jacksonville, FL where the central dispatch is located.

Answer 4

They are controlled by a train dispatcher or tower operator and set prior to a train approaching an interlocking.

Answer 5

There's several kinds of switches, but on main lines, what you'll most see are power-operated switches.

Power operated switches are usually controlled remotely by a dispatcher, tower operator, yardmaster, or switchtender.

Many of these switches (at least on CN) are what's called "dual-control switches", meaning they can be operated remotely, but also taken off power and thrown manually.  This is often the case when, for any number of reasons, the dispatcher is unable to throw the switch remotely, and they'll request that the conductor take the switch off power, then throw it themselves.