Road traffic monitoring system

• US 20040067004A1
• Filed: 07/29/2003
• Published: 04/08/2004
• 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: Hill, David John, Nash, Philip J
• Granted Patent: US 7,024,064 B2
• Time in Patent Office: Days
• US Class Current: 385/13
• CPC Class Codes: G08G 1/02 using treadles built into the road pads or other sensitive devices responsive to passage of vehicles E01F11/00
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors

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); wherein the at least one optical fibre sensor (5) comprises a former (14), an optical fibre (13) wound on the former, a casing (15) and a compliant material (16) provided between the casing and the former; such that the compliant material reduces the sensitivity of the sensor (5); and wherein the interferometric interrogation system (9) 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 (2).

Claims

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

wherein the at least one sensor station comprises at least one optical fibre sensor deployed in a highway;

wherein the at least one optical fibre sensor comprises a former, an optical fibre wound on the former, a casing and a compliant material provided between the casing and the former;

such that the compliant material reduces the sensitivity of the sensor; 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.

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 any preceding claim, wherein the optical fibre sensor further comprises at least one semi-reflective element coupled to the optical fibre.

5. A system according to claim 4, wherein the semi-reflective element is either a fibre optic X-coupler with one port mirrored or a Bragg grating.

6. A system according to any preceding claim, wherein the former comprises a cylindrical bar incorporating a helical groove.

7. A system according to claim 6, wherein the optical fibre is wound in cooperation with the helical groove.

8. A system according to any preceding claim, wherein the compliant material is one of a grease, a resin or a plastic.

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

10. A system according to claim 9, wherein the length of optical fibre connecting adjacent sensor stations is between 100 m and 5000 m.

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

12. A system according to claim 11, wherein each sensor station comprises at least one optical fibre sensor per lane of the highway.

13. A system according to claim 11 or claim 12, wherein each sensor station comprises at least two optical fibre sensors, separated from each other by a known distance, per lane of the highway.

14. A system according to claim 13, wherein the known distance is between 0.5 and 5 m.

15. 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.

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

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

18. 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;

wherein each optical fibre sensor comprises a former, an optical fibre wound on the former, a casing and a compliant material provided between the casing and the former;

such that the compliant material reduces the sensitivity of the sensor;

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.

19. A method according to claim 18, further employing wavelength division multiplexing such that the number of optical fibre sensors which the interrogation system is adapted to monitor is increased.

20. A method according to claim 18 or claim 19, further employing spatial division multiplexing such that the number of optical fibre sensors which the interrogation system is adapted to monitor is increased.

21. A method according to any of claims 18 to 20, wherein the data derived relates to vehicle speed.

22. A method according to any of claims 18 to 20, wherein the data derived relates to vehicle weight.

23. A method according to any of claims 18 to 20, wherein the data derived relates to traffic volume.

24. A method according to any of claims 18 to 20, wherein the data derived relates to axle separation.

25. A method according to any of claims 18 to 20, wherein the data derived relates to vehicle classification.