Which term refers to an apparatus that allows or prevents movements over designated routes within an interlocking?

The term that refers to an apparatus that allows or prevents movements over designated routes within an interlocking is the interlocking appliance. Interlocking appliances function as mechanisms that control signals and switches in a railway yard or station, ensuring that trains can operate safely by preventing conflicting movements. This is critical for maintaining safe distances and preventing accidents, especially where multiple tracks converge.

In contrast, blocking devices are typically used to define limits within which trains can operate, providing additional safety measures, while a traffic controller generally manages the overall flow of rail traffic rather than specifically controlling movements in an interlocking. A signal system comprises the signals themselves that communicate movement permissions to train operators but does not refer to the apparatus that physically manages the routes. Thus, the interlocking appliance is specifically designed for the purpose of controlling train movements within designated routes, making this the correct choice.