I have been putting some additional thought into the control system for my SVNO project. The plan involved using DTMF decoder relay modules, which will activate switches. This will be done with low power DTMF capable radio handhelds, which will be used for switch operation as well as communications.
So how do we make this realistic? Obviously communicating via radio in the confines of an open room seems overly pointless. However, what if we gave each operator a wireless, isolation monitor headset to wear. We could pipe a sound decoder for the locomotive they are operating, through the audio feed, as well as the radio audio and perhaps even some sounds along the way.
A small mixer could be set up to route audio for each operator. For the SVNO, it is only realistically large enough to handle 3 operators max, and one yard crew / dispatcher. An OZ Audio HM6 Q-Mix might be suitable for handling this, mixing each feed to each operator independently depending upon their route. Problem is finding one... They are quite rare now.
In any case, there could be several ways to mix and route the audio. Sensors in the track bed at crossings could trigger the sound of crossing bells in the operators ear even!