How are track signal circuits separated from others?

Track signal circuits are separated from other circuits primarily by insulated rail joints. These joints are specifically designed to provide electrical isolation between different sections of the track. This isolation is critical for the proper operation of signal systems, as it prevents interference from other electrical circuits that might cause erroneous signals or malfunctions.

Insulated rail joints can effectively break the continuity of the track's electrical circuit. By doing so, they ensure that signals relayed from one section of track do not inadvertently influence signals in adjacent sections. This is especially important in maintaining safety on rail systems, where accurate signaling is necessary to prevent accidents.

While other options like plastic barriers, wooden supports, and air gaps might play roles in structural support or physical separation in different contexts, they do not accomplish the necessary electrical isolation that insulated rail joints provide. This makes insulated rail joints the appropriate choice for ensuring that track signal circuits operate independently and reliably.