[Animats]

My favorite simulator for railway signals is NXSYS.[1] This simulates General Railway Signal's NX system down to the relay level. NX had the first "intelligent user interface" device. When a train enters the interlocking, the dispatcher pushes an entry button to indicate they want to dispatch that train. All the possible exit points then light up. The dispatcher then pushes the button at the appropriate exit light, and all the signals and switches are set up for that route.

Routing within the interlocking is automatic. Exit lights only light up if there's an available path. The system is aware of trains in the interlocking, switches locked for maintenance, and the actual position of switches, signals, and train stop devices. As a train moves through the interlocking, track space and switches are released behind it automatically, becoming available for other trains.

Today this seems routine, but it was a huge breakthrough in the 1930s. The original marketing brochure is available online.[2]

[1] https://bernardgreenberg.com/Subway/

[2] https://anyflip.com/lbes/vczg