Road traffic monitoring system

• US 20040080432A1
• Filed: 08/05/2003
• Published: 04/29/2004
• Est. Priority Date: 02/15/2001
• Status: Active Grant

• Current Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Nash, Philip J, Hill, David J
• Granted Patent: US 7,042,369 B2
• Time in Patent Office: Days
• US Class Current: 340/942
• CPC Class Codes: E01F 11/00 Road engineering aspects of Embedding pads or other sensitive devices in paving or other road surfaces , e.g. traffic detectors, vehicle-operated pressure-sensitive actuators, devices for monitoring atmospheric or road conditionspressure-sensitive elements G01L; traffic control systems G08G
• CPC Class Codes: G08G 1/01 Detecting movement of traffic to be counted or controlled G08G1/07 - G08G1/14 take precedence
• CPC Class Codes: G08G 1/02 using treadles built into the road pads or other sensitive devices responsive to passage of vehicles E01F11/00

Abstract

A traffic monitoring system comprises at least one sensor station (2) and an interferometric interrogation system (9); wherein the at least one sensor station (2) comprises at least one optical fibre sensor (5) deployed in a highway (1); and wherein the interferometric interrogation system (9) is adapted to respond to optical phase shift produced in the respond to an optical phase shift produced in the at least one optical fibre sensor.

Claims

1. A traffic monitoring system, the system comprising at least one sensor station (2) and an interferometric interrogation system (9);

wherein the at least one sensor station comprises at least one optical fibre sensor (5) deployed in a highway (10); and

wherein the interferometric interrogation system is adapted to respond to an optical phase shift produced in the at least one optical fibre sensor due to a force applied by a vehicle passing the at least one sensor station characterised in that the interferometric interrogation system comprises a Rayleigh backscatter Interferometric interrogation system.

2. A system according to claim 1, wherein the interferometric interrogation system comprises a reflectometric interferometric interrogation system.

3. A system according to claim 2, wherein the interferometric interrogation system comprises a pulsed reflectometric interferometric interrogation system.

4. A system according to claim 1, wherein the interferometric, interrogation system comprises a pulsed Rayleigh backscatter interferometric interrogation system.

5. A system according to any preceding claim, comprising a plurality of sensor stations, wherein adjacent stations are connected together by a length (3) of optical fibre.

6. A system according to claim 5, the length of optical fibre connecting adjacent sensor stations is between 100 m and 5000 m.

7. A system according to any preceding claim, wherein each sensor station comprises a plurality of optical fibre sensors.

8. A system according to claim 7, wherein each sensor station comprises at least one optical fibre, sensor per lane of the highway.

9. A system according to claim 7 or claim 8, wherein each sensor station comprises at least two optical fibre sensors, separated from each other by a known distance, per lane of the highway.

10. A system according to claim 9, wherein the known distance is between 0.5 and 5 m.

11. A system according to any preceding claim, wherein each sensor is deployed so that its longest dimension is substantially in the plane of the highway and substantially perpendicular to the direction of traffic flow on the highway.

12. A system according to any preceding claim, wherein the longest dimension of each sensor is substantially equal to the lane width of the highway.

13. A system according to any preceding claim, wherein each sensor is deployed beneath the surface of the highway.

14. A system according to any preceding claim, wherein the optical fibre sensor comprises a sensing fibre coupled to a dummy fibre;

wherein the optical path length of the sensing fibre is such that the sensitivity of the sensor is low; and

wherein the optical path length of the dummy fibre is greater than that of the sensing fibre such that the combined optical path length of the sensing fibre and the dummy fibre is sufficient to allow thee sensor to be interrogated by an interferometric interrogation system.

15. A system according to claim 14, wherein the optical path length of the dummy fibre is at least 2 times greater than that of the sensing fibre.

16. A system according to claim 14 or claim 15, wherein the sensing fibre is substantially straight.

17. A system according to any of claims 14 to 16, wherein the sensing fibre and the dummy fibre comprise sections of a single optical fibre.

18. A system according to any of claims 14 to 17, wherein the optical fibre sensor further comprises at least one semi-reflective element coupled to the optical fibre.

19. A system according to claim 18, wherein the semi-reflective element is located on the dummy fibre of the optical fibre sensor.

20. A system according to claim 18 or claim 19, wherein the semi-reflective element is either a fibre optic X-coupler with one port mirrored or a Bragg grating.

21. A system according to any of claims 14 to 20, further comprising a casing substantially surrounding at least one of the sensing fibre and the dummy fibre.

22. A system according to any of claims 1 to 13, wherein the optical fibre sensor comprises a former and an optical fibre wound on the former, wherein the former is substantially planar;

and wherein the sensor is sufficiently flexible such that it is able to substantially adopt the shape of the camber of a highway.

23. A system according to claim 22, wherein the former comprises an elongate strip provided with two spindles;

wherein the spindles are fixedly attached to the same face of the strip and disposed at a distance from each other;

wherein each spindle protrudes substantially perpendicularly from the surface of the strip; and

wherein the optical fibre is wound longitudinally between the spindles.

24. A system according to claim 22, wherein the former comprises an elongate strip and the optical fibre is wound longitudinally around the long axis of the strip.

25. A system according to claim 22, wherein the former comprises an elongate strip and the optical fibre is wound helically around the short axis of the strip.

26. A system according to any of claims 23 to 25, wherein the elongate strip comprises a metal strip.

27. A system according to any of claims 23 to 25, wherein the elongate strip comprises a non-metal.

28. A system according to any of claims 23 to 27, wherein the optical fibre sensor further comprises at least one semi-reflective element coupled to the optical fibre.

29. A system according to claim 28, wherein the semi-reflective element is either a fibre optic X-coupler with one port mirrored or a Bragg grating.

30. A method for monitoring traffic, the method comprising providing a plurality of sensor stations on a highway;

deploying a plurality of optical fibre sensors at each sensor station;

interfacing each optical fibre sensor to an interferometric interrogation system, employing time division multiplexing such that the interrogation system is adapted to monitor an output of each optical fibre sensor substantially simultaneously; and

using the output of each optical fibre sensor to derive data relating to the traffic passing each sensor station, characterised in that the interferometric interrogation system is a Rayleigh backscatter interferometric interrogation system.

31. A method according to claim 30, further employing wavelength division multiplexing such that the number of optical fibre sensors which the interrogation system is adapted to monitor is increased.

32. A method according to claim 30 or claim 31, further employing spatial division multiplexing such that the number of optical fibre sensors which the interrogation system is adapted to monitor is increased.

33. A method according to any of claims 30 to 33, wherein the data derived relates to vehicle speed.

34. A method according to any of claims 30 to 33, wherein the data derived relates to vehicle weight.

35. A method according to any of claims 30 to 33, wherein the data derived relates to traffic volume.

36. A method according to any of claims 30 to 33, wherein the data derived relates to axle separation.

37. A method according to any of claims 30 to 33, wherein the data derived relates to vehicle classification.