GB2424110A

GB2424110A - Control system for a traffic signal whereby an authorised vehicle sends its location to the signal control to change the operating mode of the traffic signal

Info

Publication number: GB2424110A
Application number: GB0427000A
Authority: GB
Inventors: Gottlieb Schwarz
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2004-12-09
Filing date: 2004-12-09
Publication date: 2006-09-13
Also published as: GB0427000D0

Abstract

A system for automatic control of a traffic signal including a transmitter on a vehicle operable to send a radio communication and a traffic signal controller associated with a traffic signal and operable to change a state of the traffic signal is disclosed. The traffic signal controller has a first independently operating mode and a second controlled mode. The traffic signal controller has a receiver to receive a communication from the vehicle and a processor to switch the mode of the traffic signal controller between it's first and second modes to let the vehicle pass through area controlled by the traffic signal. The data sent includes the current location of the vehicle, eg using a global positioning system (GPS). The processor uses the location information to determine when the vehicle is approaching a zone controlled by the associated traffic signal and accordingly to issue a trigger signal to switch the mode of the traffic signal controller. The system may monitor the vehicle to detect when the vehicle passes out the zone controlled by the traffic signal. The traffic signals may also be controlled by a central traffic control station.

Description

TITLE: SYSTEM, METHOD, CONTROLLER PND COMMUNICATION UNIT

FOR USE IN AUTOMATIC TRAFFIC SIGNAL CONTROL

FIELD OF THE INVENTION

The present invention relates to a system, a method, a controller and a communication unit for use in automatic traffic signal control. In particular, the invention relates to traffic signal control based upon the location of a public transport or other vehicle which has to be given priority to pass the traffic signal.

BACKGROUND OF THE INVENTION

In large towns and cities, public transport systems are employed wherein the location of public transport vehicles is monitored. These systems may include equipment on each vehicle which provides radio communication of information including information about location of the vehicle gathered by a location estimating device such as a GPS (Global Positioning System) terminal. Such systems also include at least one fixed vehicle traffic control station where information relating to the movement of the vehicles is received by radio communication from the vehicles and is stored and displayed on a master control screen.

Another facility available in modern public transport systems is the ability to control traffic signals such as lights from the vehicle. A unit is mounted on the vehicle which issues control messages to a traffic signal controller to take control of the traffic signal controller and thereby provide automatic switching of the associated traffic signal, e.g. by switching a light to green, when the vehicle is approaching. This allows the vehicle to pass through a zone controlled by the signal without delay. This greatly improves the efficiency of the public transport traffic flow.

In the known systems for traffic signal control, the control message from the vehicle to the traffic signal controller may be produced by a command and communication unit on the vehicle in response to a command issued by a driver or other person in charge of the vehicle, e.g. by pressing an appropriate button on the unit. Alternatively, the command and communication unit on board the vehicle may determine the location of the vehicle and, based on the determined location of the vehicle, automatically issue a radio control message to take control of the traffic signal controller and, if appropriate to cause the traffic signal controller to change (if appropriate) the traffic control signal, e.g. by changing the colour of a traffic light to green.

Similarly, when the vehicle has passed the zone controlled by the traffic control signal, another message is sent from the command and communication unit either manually or automatically based on detection of the vehicle's location. This message releases control of the traffic signal back to independent control by the traffic signal controller, e.g. if appropriate by changing a traffic light colour from green to red. The messages sent by the command and communication unit are sent in a radio signal by a dedicated radio communication system operating on a different channel from any communication system employed for communication with the vehicle traffic control station referred to earlier.

SUMMARY OF THE INVENTION

The inventor has recognised that the use in the

prior art of two separate communications systems

operating at different frequencies, one between the vehicle and the traffic signal controller and the other between the vehicle and the vehicle control station, is unnecessarily complicated and could be simplified.

According to the present invention in a first aspect there is provided a system as defined in claim 1 of the accompanying claims for automatic control of a traffic signal.

According to the present invention in a second aspect there is provided a traffic signal controller for use in the system of the first aspect, the controller being as defined in claim 15 of the accompanying claims.

According to the present invention in a third aspect there is provided a method of automatic control of a traffic signal, the method being as defined in claim 12 of the accompanying claims.

According to the present invention in a fourth aspect there is provided a communication unit for mounting on a vehicle, the unit being as defined in claim 19 of the accompanying claims.

Further features of the invention are disclosed in the accompanying dependent claims and in the description of embodiments of the invention given later in this

description.

By the invention, a traffic signal controller for automatic traffic signal control has a receiver which is operable to receive a radio communication sent by a transmitter on board a particular vehicle. The communication includes information relating to the current location of the vehicle. The communication is sent primarily to a vehicle control station but is also picked up by the receiver of the traffic signal controller. The traffic signal controller has a processor which is operable to retrieve location information from the received communication and to use the location information to determine when the vehicle is approaching or has left a zone controlled by a traffic signal associated with the controller. The traffic signal controller is operable accordingly to issue a trigger signal to switch a mode of the traffic signal controller.

Thus, the traffic signal controller does not rely on a trigger radio signal sent from the vehicle. It picks up radio signals from a communication unit on the vehicle and is able intelligently to determine when the mode of the traffic signal controller should be switched by use of the vehicle location information it retrieves from the received radio signal. Thus the invention allows use of a single communication system to provide communications between the vehicle and its control station and between the vehicle and the traffic signal controller and such a combined system is simpler to design and operate than the multiple systems used in the

prior art.

The vehicle which is given priority to pass a given controlled zone using the system, controller and method of the invention may be a public transport vehicle such as a bus, tram or train although it could alternatively be an emergency services vehicle such as a police car or other police vehicle, an ambulance, a doctor's or paramedic's vehicle or a fire services vehicle.

The location information sent to the control station may be sent frequently at regular intervals, e.g. every 5 seconds, and the traffic signal controller may therefore receive more than one communication of location information prior to the vehicle reacing the controlled zone. Beneficially, this can help to improve the accuracy of the location information the controller retrieves. In contrast, in the prior art, communication units on vehicles send location information only when certain events occur, e.g. if they cross a controlled zone. Further accuracy can be achieved if also information relating to speed, stops made, times of such stops etc, of the monitored vehicle is used in the calculations made by the traffic signal controller.

Signals additional to those employed to send location information may be used to send additional information.

So, the traffic signal controller could have significant intelligence.

A further benefit of using the same communication signals from the communication unit on the vehicle as for communication with the control station, is that the control station could remotely take over control of the controller, e.g. in special situations, e.g. when escorted cars have to be given priority to cross the controlled intersection at a specified time.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a street layout illustrating traffic signal control by an embodiment of the invention.

FIG. 2 is a block schematic diagram showing more detail of a traffic signal controller shown in FIG. 1.

FIG. 3 is a block schematic diagram showing more detail of a control station shown in FIG. 1.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A street layout 100 is shown in FIG. 1. A first public transport vehicle 101 is travelling along a first street 102 and a second public transport vehicle 103 is travelling along a second street 104 running perpendicular to the first street 102. The first street 102 crosses the second street 104 at an intersection region 105. Other traffic is present in the street layout 100 but for simplicity is not shown in FIG. 1.

Traffic flow across the intersection 105 is controlled by a set of traffic light indicators 108.

Each traffic light indicator 108 of the set includes at least a red light and a green light. It may include also an amber light depending on the light sequence normally used by the set. All of the indicators 108 of the set show the same light at the same time for a given direction of traffic flow. Within a controlled zone 109 shown enclosed by a dashed line, traffic is allowed to proceed in one direction only at a time across the intersection 105. A traffic light controller unit 113 is connected to the traffic light indicators 108 and controls operation of the traffic light indicators 108 so that for each given traffic flow period, say 20 seconds, when traffic is allowed to move across the intersection 105, only that traffic in the controlled zone 109 which is to travel in one particular direction, say to continue along the first street 104 from left to right as seen in FIG. 1, is allowed to move across the intersection 105. Conventionally, the traffic light control unit 113 issues signals to the traffic light indicators 108 to show either green or red depending on the direction they are facing to permit the correct directional flow during each traffic flow period. Thus, for each traffic light indicator 108 the colour shown alternates between red and green during the traffic flow periods. In between each traffic flow period there is also a traffic stop period in which traffic in the controlled zone 109 is stopped from crossing the intersection 105 in all directions to clear the intersection 105 of already moving traffic.

During normal operation of the traffic light indicators 108, when no public transport or other priority vehicle is approaching the intersection 105, the traffic light controller unit 113 independently controls changes of the lights shown by the indicators 108 so that traffic in all directions is given an opportunity to cross the intersection 105 after appropriately waiting its turn. However, when the vehicle 101 approaches the intersection 105 as shown in FIG. 1, operation of the control unit 113 changes to a controlled mode wherein the vehicle 101 is given priority to cross the intersection 105 without stopping.

This controlled mode is achieved in manner to be described as follows.

A command and communication unit 114 is mounted on the vehicle 101. A similar command and communication unit 115 is mounted on the vehicle 103 and similar units are mounted on other public transport vehicles operating in the town or city having the street layout 100. The unit 114, the unit 115 and other similar units (not shown) send radio communications to a public transport vehicle control station 116 to be described in more detail later. Communications 117 and 118 from the units 114 and 115 respectively are shown in FIG. 1. The information contained in each communication includes an estimate of the current location of the vehicle. Thus, the information in the communication 117 from the unit 114 on the vehicle 101 indicates the current location of the vehicle 101. This may for example have been estimated using a GPS (Global Positioning System) receiver included in the command and communication unit 114. The radio communications from the command and control units on board each of the public transport vehicles which are sent to the control station 116 are also picked up by the traffic light controller units.

Thus, the communication 117 from the command and control unit 114 on the vehicle 101 is picked up by the traffic light controller unit 113 as well as by the control station 116.

The traffic light controller unit 113 is shown in more detail in FIG 2. The controller unit 113 includes a receiver 120 which is able to pick up the communication 117, a processor 121 which is able to process data, including information retrieved from the received communication 117, a memory 122 which stores data and programs used to operate the processor 121 and other components of the unit 113 as well as information received in communications such as the communication 117. The controller unit 113 also includes a mode switch 123 and a light operation selector 124. The processor 121 is able to use the received location information included in the communication 117 to determine a direction in which the vehicle 101 is travelling and to determine when the vehicle 101 is approaching the controlled zone 109. For example, the processor 121 may determine when the vehicle 101 is estimated to be within metres of the controlled zone 109. When the processor 121 makes that determination it issues a trigger signal which switches the state of the mode switch 123. The state of the mode switch 123 determines the operational mode of the light operation selector 124. The selector 124 operates either in an independent mode or in a controlled mode. In the independent mode the traffic light indicators 108 are periodically switched in a sequence without reference to any approaching vehicle. In the controlled mode the traffic light indicators 108 are set to show a green light to a vehicle detected to be approaching and to be given priority to pass through the intersection 105. Thus, when the state of the mode switch 122 is changed by the processor 121 when it determines that the vehicle 101 is sufficiently close to the controlled zone 109, the mode of the light operation selector 124 is switched from independent to controlled to allow the vehicle 101 to pass freely through the intersection 105.

When the vehicle 101 has passed the controlled zone 109 by a sufficient distance, say 100 metres, this is detected by the processor 121 of the traffic light controller 113 again by location information in the received communication 117. The processor 121 issues a further trigger signal to change the state of the mode switch 123 which causes the mode of the light operation selector 124 to be changed back to the independent mode.

This continues until a further vehicle is detected by the processor 121 to be approaching the controlled zone 109.

As noted earlier, the communication 117 from the unit on the vehicle 101 and similar communications from units on other vehicles are sent to the public transport vehicle control station 116 which is shown in more detail in FIG. 3. The control station 116 includes a receiver 125, a processor 126, a memory 127, a transmitter 128, a control terminal 129 and a display 130. The receiver 125 receives the communications such as the communication 117 and decodes the communications.

The information in them is stored in a database held in the memory 127. The information contained in each communication and retrieved by the control station 116 includes as well as the location information referred to earlier an identifier of the vehicle carrying the unit sending the communication, e.g. an identifier of the unit 114 for the communication 117. The processor 126 uses the identification and location information to produce a map of the current location of identified vehicles operating in the transport system and the map is displayed in graphical form on the display 130.

Personnel acting as control managers of the transport system can observe the displayed map on the display 130 to monitor that the vehicle movement is operating satisfactorily and can send and receive related communications at the control terminal 129. For example, if problems arise in the traffic flow involving public transport vehicles, the control manager is able to communicate with drivers of relevant vehicles by radio from the control terminal 129. Communications to or from the control terminal 129 are sent via the receiver 125 or transmitter 128 as appropriate. The system employed to send the vehicle identifier and location signals to the control station 116 may also be used to send communications to the individual vehicles.

Thus, the transmitter 125 of the control station 116 may be used to transmit speech information from a manager at the control terminal 129 to a receiver included in the unit 114 on the vehicle 101 and conversely a transmitter included in the unit 114 may be used to send speech information to the control terminal 129 via the receiver 124 (or directly if appropriate) . The communication system employed and enhanced to provide the various operational functions described herein may be a trunked system designed to operate in accordance with TETRA (Terrestrial Trunked Radio) industry standards as defined by the European Telecommunications Standards The vehicle control station 116 also sends out via the transmitter 115 a broadcast radio communication 131.

This is picked up by the traffic li ght controller units such as the unit 113. In this way, information about the identity and current location of public transport vehicles is provided. The processors of the traffic light controller units such as the processor 121 of the unit 113 are able to use this information to filter out unwanted communications from vehicles which are not approaching, such as, in the case of the unit 113, the communication 115 from the unit on board the vehicle 103.

In situations where vehicles are approaching the controlled intersection 105 from different directions at the same time, the processor 121 of the controller 113 may operate an algorithm which provides a preference of one vehicle over the other. For example, the memory 122 of the controller 113 may store information relating to the timetables of the vehicles, and the vehicle which is currently more delayed (or less in advance) in relation to its timetable may have precedence. The pre-defined timetables for the particular vehicles identified could for example be broadcast by the control station 116 to traffic signal controllers such as the controller 113 in advance, e.g. overnight.

Claims

1. A system for automatic control of a traffic signal including (i) a transmitter on a vehicle operable to send a radio communication; (ii) a traffic signal controller associated with a traffic signal and operable to change a state of the traffic signal, the traffic signal controller having a first independently operating mode and a second controlled mode wherein an identified approaching vehicle is allowed to pass through a zone controlled by the traffic signal, the traffic signal controller including a receiver operable to receive a communication from the transmitter on the vehicle and a processor operable in response to the communication to switch the mode of the traffic signal controller between its first and second modes; and characterised in that the receiver is operable to receive a communication sent by the transmitter which includes information relating to the current location of the vehicle, and the processor is operable to retrieve location information from the received communication and to use the location information to determine when the vehicle is approaching a zone controlled by the associated traffic signal and accordingly to issue a trigger signal to switch the mode of the traffic signal controller.

2. A system according to claim 1 wherein the processor is operable to estimate when the vehicle has reached a given distance from the zone controlled by the associated traffic signal and to issue a trigger signal accordingly to switch the mode of the traffic signal controller.

3. A system according to any one of the preceding claims wherein the processor is operable to detect when the vehicle has passed the zone controlled by the traffic signal.

4. A system according to claim 3 wherein the processor is operable to detect when the vehicle has passed the traffic signal and has reached a given distance from the zone controlled by the traffic signal and to issue a trigger signal accordingly to release control of the traffic signal controller.

5. A system according to any one of the preceding claims wherein the receiver is operable to receive a signal including information which identifies the vehicle or its transmitter, and the processor of the traffic signal controller is operable to employ the information to filter signals from transmitters on vehicles other than the identified vehicle.

6. A system according to any one of the preceding claims wherein the transmitter on the vehicle is operable to send the signal including information which identifies the vehicle.

7. A system according to any one of the preceding claims and including a vehicle control station having a receiver which also receives the communication sent by the transmitter on the vehicle and a processor which retrieves the location information.

8. A system according to claim 5 and including a vehicle control station having a receiver which also receives the communication sent by the transmitter on the vehicle and a processor which retrieves the location information wherein the traffic control station includes a transmitter operable to send the signal including information which identifies the vehicle.

9. A system according to any one of the preceding claims which includes a plurality of transmitters each on an associated vehicle and each operable to send a signal including information relating to its respective location and a plurality of traffic signal controllers each associated with a respective traffic signal and each operable to change a state of its associated traffic signal, each of the traffic signal controllers being operable to detect the signal sent by one of the vehicles when approaching or having passed the zone controlled by its associated traffic signal.

10. A system according to claim 9 and including a traffic control station including a receiver operable to receive the signals from the transmitters on the vehicles including location and a transmitter operable to broadcast a signal including information which identifies vehicles and their current location, the receiver of each of the traffic signal controllers being operable to receive the broadcast signal and the signal processor of each of the traffic control units is operable to extract information from the received broadcast signal to identify a signal sent from a transmitter on a nearby vehicle and to filter signals from transmitters on other vehicles.

11. A system according to any one of the preceding claims wherein the traffic signal comprises a set of traffic lights of switchable colour.

12. A method of automatic control of a traffic signal including (i) changing the state of a traffic signal by an associated traffic signal controller, receiving by a receiver associated with the traffic signal controller a signal relating to the location of a vehicle and, when the vehicle is approaching, causing the traffic signal controller to control the state of the traffic light to allow the approaching vehicle to pass a zone controlled by the traffic light; and (ii) sending from a transmitter on the vehicle to a vehicle traffic control station a signal including information relating to the location of the vehicle; and characterised in that the receiver also receives the signal sent by the transmitter to the traffic control station, and the signal processor extracts location information from the received signal and determines when the vehicle is approaching a zone controlled by the associated traffic signal and accordingly issues a trigger signal to switch a mode of the traffic signal controller.

13. A method according to claim 12 wherein communications from the transmitter on the vehicle which include location information are sent at regular intervals.

14. A method according to claim 12 or claim 13 wherein in special situations the traffic control station takes over control of the traffic signal controller.

15. A traffic signal controller operable to change a state of an associated traffic signal, the traffic signal controller having a first independently operating mode and a second controlled mode wherein an identified approaching vehicle is allowed to pass through a zone controlled by the traffic signal, the traffic signal controller including a receiver operable to receive a communication from a transmitter on the identified vehicle and a processor operable in response to the communication to switch the mode of the traffic signal controller between its first and second modes; and characterised in that the receiver is operable to receive a communication sent by the transmitter which includes information relating to the current location of the identified vehicle, and the processor is operable to retrieve location information from the received communication and to use the location information to determine when the identified vehicle is approaching a zone controlled by the associated traffic signal and accordingly to issue a trigger signal to switch the mode of the traffic signal controller.

16. A traffic signal controller according to claim 15 wherein the processor of the controller is also operable to retrieve information related to one or more of the speed of the vehicle, stops made by the vehicle and times of stops made by the vehicle.

17. A traffic signal controller according to claim 15 or claim 16 wherein the processor is operable, when two or more vehicles are approaching the controlled zone, to apply a procedure to decide which of two approaching vehicles should be given precedence to cross the controlled zone first.

18. A traffic signal controller according to any one of claims 15 to 17 wherein the receiver is operable to receive a communication from a vehicle control station and the processor is operable to retrieve from the communication information relating to the identity of moving vehicles.

19. A communication unit for mounting on a vehicle for use in the system according to any one of claims 1 to 11 or in the method according to any one of claims 12 to 14 the unit being operable to send regular communications including information relating to the current location of the vehicle.

20. A communication unit according to claim 19 and which is operable to send communications to a control station and/or to receive communications from a control station.

21. A system according to any one of claims 1 to 11 and substantially as herein described with reference to any one or more of the accompanying drawings.

22. A method according to any one of claims 12 to 14 and substantially as herein described with reference to any one or more of the accompanying drawings.

23. A traffic signal controller according to any one of claims 15 to 17 and substantially as herein described with reference to FIG. 2 of the accompanying drawings.

24. A communication unit according to claim 19 or claim and substantially as herein described with reference to the accompanying claims.