Editing Automatic vehicle location (section)

=== Signpost systems ===
To track and locate vehicles along fixed routes, a technology called '''Signpost transmitters''' is employed. This is used on transit routes and rail lines where the vehicles to be tracked continually operated on the same linear route. A [[transponder]] or RFID chip along the vehicle route would be polled as the train or bus traverses its [[Thoroughfare|route]]. As each transponder was passed, the moving vehicle would query and receive an [[acknowledgement (data networks)|ack]], or handshake, from the signpost transmitter. A transmitter on the mobile would report passing the signpost to a system controller. This allows supervision, a [[call center]], or a [[dispatcher|dispatch]] center to monitor the progress of the vehicle and assess whether or not the vehicle was ''on schedule''. These systems are an alternative inside tunnels or other conveyances where GPS signals are blocked by terrain.<ref>For an example of one US signpost system, see its service manual: ''T1919A Metrocom II 150.8-174 MHz Vehicle Location Receiver'', (Schaumburg, Illinois: Motorola Communications and Electronics, 1979).</ref>