TRAFFIC SIGNALS CONTROL SYSTEM

• US 20090322561A1
• Filed: 06/04/2009
• Published: 12/31/2009
• Est. Priority Date: 06/04/2008
• Status: Active Grant

• Current Assignee: Roads and Maritime Services
• Original Assignee: Roads & Traffic Authority of New South Wales
• Inventors: Morioka, Nobuyuki, Hengst, Bernhard, Huang, Eric Enyang
• Granted Patent: US 8,212,688 B2
• Time in Patent Office: Days
• US Class Current: 340/907
• CPC Class Codes: G08G 1/08 according to detected number or speed of vehicles

Abstract

A method of controlling traffic signals at a road intersection, which has a plurality of signal groups, each of which controls at least one direction of traffic within the intersection. The method comprises the steps of obtaining and utilising traffic data to calculate a current traffic state and the rate of change in the traffic state. The method further comprises formulating at least one action and the duration of the action in response to these calculations. Each action comprises switching at least one traffic signal. One or more policies based on the calculations and the action are resolved. A continuous decision making process is applied to evaluate a reward for the policies resolved and a policy that maximizes the reward is selected.

Claims

1. A method of controlling traffic signals at a road intersection which has a plurality of signal groups, each of which controls at least one direction of traffic within the intersection, the method comprising the steps of:

(i) obtaining and utilising traffic data to calculate a current traffic state and the rate of change in the traffic state;

(ii) formulating at least one action and the duration of said action in response to the calculations obtained in step (i), wherein each action comprises switching at least one traffic signal;

(iii) resolving one or more policies based on the calculations obtained in step (i) and the action formulated in step (ii);

(iv) applying a continuous decision making process to evaluate a reward for the policies resolved in step (iii); and

(v) selecting a policy that maximizes the reward.

2. A method of claim 1 wherein the current traffic state comprises one or more of traffic queue length, vehicle speed, vehicle position, vehicle type, and arrival rate.

3. A method of claim 1 wherein the current traffic state comprises a traffic queue length and the rate of change is the rate of growth of the traffic queue.

4. A method of any one of claims 1 wherein the continuous decision making process comprises a semi-Markov Decision Process.

5. A method of claim 4 wherein the continuous decision making process comprises an optimisation for the semi-Markov Decision Process.

6. A method of claim 5 wherein the optimisation comprises the steps of:

(i) generating a policy pathway comprising a plurality of different paths, each path having a one or more nodes, which represent at least one policy; and

(ii) evaluating a reward for each path in the policy pathway by evaluating and totaling the reward of the policies located at each node along each one of the different paths.

7. A method of claim 6 wherein the optimisation is adapted to terminate when a termination condition is reached within the policy pathway.

8. A method of claim 7 wherein the termination condition is selected from one or more of the node count limit, the time count limit or the storage count limit.

9. A method of claim 6 wherein the evaluated reward is a value of a function for optimising at least one traffic condition.

10. A method of claim 9 wherein the traffic condition is any one or more of vehicle fuel consumption, pollution, the number of vehicle stops, vehicle waiting time and time delay.

11. A method of claim 1, wherein the continuous decision making process comprises a set of states and a set of actions for transitioning between states and a policy comprises mapping states to actions, wherein a state comprises at least one signal group state and one traffic state.

12. A method of claim 11, wherein the signal group state comprises a plurality of signals and a counter for each signal.

13. A method of claim 12, wherein the signals comprise red and green.

14. A method of claim 12, wherein the counter stores an amount of time remaining before the signal can be switched.

15. A method of claim 1, wherein the traffic data is collected by the use of sensors.

16. A method of claim 15, wherein the sensor comprises any one or more of loop detector, video camera, radar device, infra-red sensor, RFID tag or GPS device.

17. A method of claim 1, wherein the step of calculating the traffic state comprises the step of determining the end-of-queue of the incoming traffic.

18. A method of claim 17 wherein the end-of-queue is determined using total space-time and number of spaces.

19. A traffic signals control system comprising a control means for controlling actuators for the controlling of traffic signals at a road intersection which has a plurality of signal groups, each of which controls at least one direction of traffic within the intersection, and a traffic modeling means arranged to receive traffic data from a sensor means, the control means being operable to:

(i) obtain and utilise the traffic data to calculate a current traffic state and the rate of change in the traffic state;

(ii) formulate at least one action and the duration of said action in response to the calculations obtained in step (i), wherein each action comprises switching at least one traffic signal;

(iii) resolve one or more policies based on the calculations obtained in step (i) and the action formulated in step (ii);

(iv) apply a continuous decision making process to evaluate a reward for the policies resolved in step (iii); and

(v) select a policy that maximizes the reward.

20. The traffic control system of claim 19 wherein the current traffic state comprises one or more of traffic queue length, vehicle speed, vehicle position, vehicle type, and arrival rate.

21. The traffic control system of claim 19 wherein the current traffic state comprises a traffic queue length and the rate of change is the rate of growth of the traffic queue.

22. The traffic control system of claim 19 wherein the continuous decision making process comprises a semi-Markov Decision Process.

23. The traffic control system of claim 22 wherein the continuous decision making process comprises an optimisation for the semi-Markov Decision Process.

24. The traffic control system of claim 23 wherein the optimisation includes:

(i) generating a policy pathway comprising a plurality of different paths, each path having a one or more nodes, which represent at least one policy; and

(ii) evaluating a reward for each path in the policy pathway by evaluating and totaling the reward of the policies located at each node along each one of the different paths.

25. The traffic control system of claim 24 wherein the optimisation is adapted to terminate when a termination condition is reached within the policy pathway.

26. The traffic control system of claim 25 wherein the termination condition is selected from one or more of the node count limit, the time count limit or the storage count limit.

27. The traffic control system of claim 24 wherein the evaluated reward is a value of a function for optimising at least one traffic condition.

28. The traffic control system of claim 27 wherein the traffic condition is any one or more of vehicle fuel consumption, pollution, the number of vehicle stops, vehicle waiting time and time delay.

29. The traffic control system of claim 20, wherein the continuous decision-making process comprises a set of states and a set of actions for transitioning between states and a policy comprises mapping states to actions, wherein a state comprises at least one signal group state and one traffic state.

30. The traffic control system of claim 29, wherein the signal group state comprises a plurality of signals and a counter for each signal.

31. The traffic control system of claim 30, wherein the signals comprise red and green.

32. The traffic control system of claim 30, wherein the counter stores an amount of time remaining before the signal can be switched.

33. The traffic control system of claim 19, wherein the traffic data is collected by the use of sensors.

34. The traffic control system of claim 33, wherein the sensor comprises any one or more of loop detector, video camera, radar device, infrared sensor, RFID tag or GPS device.

35. The traffic control system of claim 19, wherein the step of calculating the traffic state comprises the step of determining the end-of-queue of the incoming traffic.

36. The traffic control system of claim 35 wherein the end-of-queue is determined using total space-time and number of spaces.