Patent GB-1355803-A (GB)
Title: Road traffic information communication system
IPC: G08G1/0967
Filed: 1970-12-03
Abstract: 1355803 Radio signalling; radio receivers STANDARD TELEPHONES & CABLES Ltd 2 Dec 1971 [3 Dec 1970] 57454/70 Headings H4L and H3Q [Also in Division G4] A road-traffic information communication system comprises a roadside message transmitter associated with two pairs of single-frequency roadside transmitters which act to enable a given vehicle receiver channel so that the vehicle will receive routine information regarding the roadway and route ahead or emergency information, appropriate to the vehicle direction of travel. In the embodiment shown (Fig. 2) a message transmitter 201 having a short range omnidirectional aerial transmits information on two channels the information being relevant, respectively, to separate traffic flow directions. A first pair of single frequency "beacons" 203, 205 with unidirectional aerials transmit different respective frequencies F1, F2 across both lanes of traffic flow. A similar, second pair of beacons 202, 204 transmits respective frequencies F1, F3. A receiver of the vehicle embodies a channel selector arrangement responsive to particular combinations of the frequencies which are received in a given sequence to select the message channel relevant to the vehicle direction of travel. In the vehicle receiver (Fig. 4) selection and rejection of channels is effected by a logic circuit; for example, if F1 is present but other beacon frequencies F2, F3 and F4 are not present, gate 401a will open. If, subsequently, F2 and not F1, F3 and F4 appear, gate 401b opens. As a result, flip-flops 403a, 403b are set and enable the channel selector 405a which allows the audio output of channel 1 to be passed via gate 407 (when open) to the amplifier 406 and hence loud-speaker 410. When the channel has been so selected, no output occurs until a pre-message announcement tone is detected by a detector 408. This then opens gate 407. Detector 408 also drives a divide-by-three circuit 409 which, after two complete message repetitions have been received, (i.e. when a third tone is received), closes gate 407. An OR gate 415 provides an output which can be used to inhibit reception of any normal radio braodcast to which the vehicle occupant may be listening. To allow traffic messages to be received via the normal vehicle radio loud-speaker, the arrangement of Fig. 5 is provided. This will receive normal AM broadcasts which are overridden when the appropriate beacons are passed. With the vehicle ignition switch 500 closed, the UHF message-receiving circuits 501 are energized, but no message is heard until a set of beacons is passed; then a message channel is selected as above and a power relay 502 is operated to switch on the audio amplifier stage 503 of the normal vehicle radio. If the AM radio 505 is switched on at switch 504, the UHF receiver also operates a muting switch in the AM receiver 505 to provide the necessary override. The roadside transmitters are low-power, battery-operated UHF devices disposed spatially so that vehicles will receive at least two complete message repetitions. The message transmitter embodies one or more tape loops holding one message per channel, and record and playback devices.