Alarm and identification features of the Southern California rapid transit district bus radio system

The Southern California Rapid Transit District (SCRTD) two-way radio system now in service provides voice communication and a silent alarm feature for safety purposes. The same equipment also provides automatic transmitter identification. These features have been accomplished using an added logic assembly installed in the driver's area of the bus not far from the handset hanger. The equipment sends four digits of vehicle identification, six digits of assignment information, and one digit of message type marking, generated with integrated circuit logic and transmitted with keyed audio tone. The assignment information is determined by a code card plugged in by the driver at the start of an assignment. At the base station, the information transmitted from each bus is first presented on a visual display in front of the dispatcher, recorded on a digital printer with a time code, and then analyzed for alarm and acknowledgment significance. In the event of an alarm, the location of the bus is known from the complete identification of route and run number. This information is used by dispatchers to provide rapid police assistance in emergencies.