3644883 is referenced by 123 patents and cites 3 patents.

In a computer-controlled bus-monitoring system, each of the buses in the system is provided with a two-way radio for communication with the control center on either a voice channel or a data channel. In addition, each bus includes a second receiver for receiving signals from signpost transmitters located along the route, with the signpost information being stored in a temporary storage unit in the bus. The computer continually controls interrogation of all of the buses in the system on a data channel, with the buses automatically replying with the stored signpost location plus the time elapsed since that signpost location was stored in the bus. Deviations from schedule are displayed on a control console at the control center. The bus may be alerted to reply on a voice channel by a special code sent over the data channel with selective calling of the particular bus being provided, and a provision also is made for alerting the control center of an emergency on the bus by automatic data transmission from the bus over the voice channel.

Title
Automatic vehicle monitoring, identification, location, alarm and voice communications system
Application Number
04/888,519
Publication Number
3644883
Application Date
December 29, 1969
Publication Date
February 22, 1972
Inventor
Walker Donald L
Borman William M
Assignee
Motorola
IPC
G08g 01/12
G08G 01/127
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