Non-intrusive traffic monitoring system

• US 20040249561A1
• Filed: 02/26/2004
• Published: 12/09/2004
• Est. Priority Date: 02/27/2003
• Status: Active Grant

• Current Assignee: Spectra Research, Inc.
• Original Assignee: Spectra Research, Inc.
• Inventors: Johnson, Michael R., Zidek, Paul D., Little, Gordon R., Capozzi, Jerry V.
• Granted Patent: US 7,107,144 B2
• Time in Patent Office: Days
• US Class Current: 701/117
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors

Abstract

A traffic monitoring system including a non-intrusive lane monitor is provided. The lane monitor comprises one or more laser channels, a user interface, and a programmable controller in communication with the laser channels and the user interface. In accordance with one embodiment of the present invention, a pair of laser channels are provided. The first laser axis is substantially parallel to the second laser axis and the first and second laser axes lie substantially in a common horizontal plane. The programmable controller is configured to generate reflected laser pulse count corresponding to reflection of a pulsed laser signal from a target positioned along one of the laser axes and identify the reflected signal as a valid or invalid target by comparing the pulse count to a predetermined valid target count.

Claims

1. A traffic monitoring system comprising a non-intrusive lane monitor, said lane monitor comprising first and second laser channels, a user interface, and a programmable controller in communication with said first and second laser channels and said user interface, wherein:

said first laser channel comprises a first laser source and a first laser receiver;

said first laser source is configured to generate a first pulsed laser signal along a first laser axis;

said first laser receiver is configured to detect individual reflected laser pulses from said first pulsed laser signal;

said second laser channel comprises a second laser source and a second laser receiver;

said second laser source is configured to generate a second pulsed laser signal along a second laser axis;

said second laser receiver is configured to detect individual reflected laser pulses from said second pulsed laser signal;

said first laser axis is substantially parallel to said second laser axis;

said first and second laser axes lie substantially in a common horizontal plane;

said first laser axis is offset from said second laser axis in said common horizontal plane by a laser channel offset distance x; and

said programmable controller is configured to;

generate reflected laser pulse count corresponding to reflection of a pulsed laser signal from a target positioned along one of said laser axes, and

identify said reflected signal as a valid or invalid target by comparing said pulse count to a predetermined valid target count.

2. A traffic monitoring system as claimed in claim 1 wherein said programmable controller is configured to generate said first and second laser signals at a pulse repetition frequency of between about 5 kHz and about 10 kHz.

3. A traffic monitoring system as claimed in claim 1 wherein said programmable controller is configured to generate said first and second laser signals at a pulse repetition frequency of between about 5 kHz and about 10 kHz and a pulse duration of less than about 20 ns.

4. A traffic monitoring system as claimed in claim 1 wherein said programmable controller is configured to generate said first and second laser signals at a pulse repetition frequency PRF that varies as a function of a detected vehicle speed.

5. A traffic monitoring system as claimed in claim 1 wherein said programmable controller is configured to generate said first and second laser signals at a pulse repetition frequency PRF of at least about:

6. A traffic monitoring system as claimed in claim 4 wherein said expected average target speed is at least about 5 mph (40 km/h).

7. A traffic monitoring system as claimed in claim 4 wherein said channel offset distance x is less than about 3 ft (90 cm).

8. A traffic monitoring system as claimed in claim 4 wherein said channel offset distance x is about 1 ft (30 cm).

9. A traffic monitoring system as claimed in claim 4 wherein said channel offset distance x is less than about 3 ft (90 cm) and said expected average target speed v is at least about 25 mph (40 km/h).

10. A traffic monitoring system as claimed in claim 4 wherein said channel offset distance x is about 1 ft (30 cm) and said expected average target speed v is about 55 mph (90 km/h).

11. A traffic monitoring system as claimed in claim 1 wherein said programmable controller is configured to generate said first and second laser signals at a pulse repetition frequency sufficient to generate a plurality of reflected pulses as less than 4 inches (10 cm) of a target moving at a speed v intercepts one of said pulsed laser signals, said speed v being at least about 25 mph (40 km/h).

12. A traffic monitoring system as claimed in claim 11 wherein said pulse repetition frequency is sufficient to generate said plurality of reflected pulses as less than 3 inches (7.5 cm) of a target moving at a speed v intercepts one of said pulsed laser signals.

13. A traffic monitoring system as claimed in claim 11 wherein said pulse repetition frequency is sufficient to generate said plurality of reflected pulses as less than 1 inch (2.5 cm) of a target moving at a speed v intercepts one of said pulsed laser signals.

14. A traffic monitoring system as claimed in claim 11 wherein said speed v is at least about 55 mph (90 km/h).

15. A traffic monitoring system as claimed in claim 11 wherein said pulse repetition frequency is sufficient to generate at least eight reflected pulses as less than 4 inches (10 cm) of a target moving at a speed v intercepts one of said pulsed laser signals, said speed v being at least about 25 mph (40 km/h).

16. A traffic monitoring system as claimed in claim 15 wherein said speed v is at least about 55 mph (90 km/h).

17. A traffic monitoring system as claimed in claim 11 wherein said pulse repetition frequency is sufficient to generate at least sixteen reflected pulses as less than 4 inches (10 cm) of a target moving at a speed v intercepts one of said pulsed laser signals, said speed v being at least about 25 mph (40 km/h).

18. A traffic monitoring system as claimed in claim 17 wherein said speed v is at least about 55 mph (90 km/h).

19. A traffic monitoring system as claimed in claim 11 wherein said pulse repetition frequency is sufficient to generate greater than 8 reflected pulses as less than 1 inch (2.5 cm) of a target moving at a speed v intercepts one of said pulsed laser signals, said speed v being at least about 55 mph (90 km/h).

20. A traffic monitoring system as claimed in claim 1 wherein said programmable controller is configured to:

reject signal reflections of invalid targets; and

re-initiate reflected pulse counting following a number of receiver-disabled counts sufficient in quantity to substantially decrease the likelihood of farther reflections from said invalid target.

21. A traffic monitoring system as claimed in claim 1 wherein said controller is programmed to:

enable generation and detection in one of said first and second laser channels while inhibiting generation and detection in the other of said first and second laser channels; and

alternate said generation of said first and second pulsed laser signals along said respective first and second laser axes.

22. A traffic monitoring system as claimed in claim 1 wherein said programmable controller is configured to determine respective times-of-flight of said reflected laser pulses and correlate said respective times-of-flight with predetermined roadway lanes.

23. A traffic monitoring system as claimed in claim 22 wherein said programmable controller is configured to establish a maximum timing gate width T_G(max) for detection of said reflected laser pulses that corresponds to:

T_G(max)≈

2R_max/c

where R_max corresponds to a maximum detection range for said predetermined roadway lanes and c is the speed of light.

24. A traffic monitoring system as claimed in claim 22 wherein said programmable controller is configured to convert said time-of-flight correlations to a simulated contact switch signal and transmit said simulated contact switch signal to a host traffic counting unit.

25. A traffic monitoring system as claimed in claim 22 wherein said programmable controller is configured to determine said respective times-of-flight by accounting for a laser firing delay T_M and a roadway offset delay T_O of said lane monitor.

26. A traffic monitoring system as claimed in claim 22 wherein said programmable controller is configured to:

identify successive reflected laser pulses correlated with a common roadway lane and received by different ones of said first and second receivers; and

determine vehicle speed from an elapsed time between said successive reflected laser pulses.

27. A traffic monitoring system as claimed in claim 1 wherein said first and second laser sources are configured to generate pulsed laser signals characterized by substantially mono-directional divergence in a horizontal plane.

28. A traffic monitoring system as claimed in claim 1 wherein:

said first and second laser sources are configured to generate pulsed laser signals having cross sectional beam profiles characterized by respective major axes of divergence; and

said first and second laser sources are configured such that said major axes of divergence lie in a substantially horizontal plane.

29. A traffic monitoring system as claimed in claim 1 wherein said first and second laser sources are configured to:

generate pulsed laser signals along a horizontal plane; and

generate pulsed laser signals characterized by cross-sectional profiles defining substantially vertical edges.

30. A traffic monitoring system as claimed in claim 1 wherein:

said first laser source and said first laser receiver define a substantially co-axial configuration; and

said second laser source and said second laser receiver define a substantially co-axial configuration.

31. A traffic monitoring system as claimed in claim 1 wherein:

said first laser source and said first laser receiver define an offset configuration;

said second laser source and said second laser receiver define an offset configuration; and

said offset of said respective sources and receivers is compensated for by configuring respective fields of view of said receivers to account for said offset.

32. A traffic monitoring system as claimed in claim 1 wherein respective fields of view of said receivers are configured to avoid inclusion of reflections originating from points substantially above a horizontal plane of said receivers.

33. A traffic monitoring system as claimed in claim 32 wherein said respective fields of view defined by said first and second laser receivers are configured by truncating said fields of view, tilting said fields of view relative to a horizontal plane, or combinations thereof.

34. A traffic monitoring system as claimed in claim 1 wherein said first and second laser sources are configured such that first and second laser axes are substantially parallel, lie at substantially identical elevations, and define a substantially equal cross-sectional areas.

35. A traffic monitoring system as claimed in claim 1 wherein said laser channel offset distance x is between about 15 cm and about 90 cm.

36. A traffic monitoring system as claimed in claim 1 wherein said first and second laser sources comprise beam expansion optics configured to increase respective beam diameters of said pulsed laser signals to at least about 2.5 cm within a detection range of a set of predetermined roadway lanes.

37. A traffic monitoring system as claimed in claim 1 wherein said first and second laser sources are configured to generate said first and second laser signals at a laser irradiance no greater than about 100 mW/cm² for a wavelength of about 1550 nm.

38. A traffic monitoring system as claimed in claim 1 wherein said first and second laser sources are configured to generate said first and second laser signals at a laser irradiance no greater than about 1 mW/cm² for wavelengths of between about 700 nm and about 1050 nm.

39. A traffic monitoring system as claimed in claim 1 wherein said lane monitor comprises at least one constant fraction discrimination circuit configured to account for differences in respective rise times of laser pulses reflected from surfaces of differing reflectivity at a common range.

40. A traffic monitoring system as claimed in claim 39 wherein said constant fraction discrimination circuit is configured to combine a detected reflected signal pulse with a delayed, inverted replica to obtain a signal that is substantially independent of pulse amplitude.

41. A traffic monitoring system as claimed in claim 1 wherein said lane monitor comprises a spectral filter associated with each laser receiver to block background radiation.

42. A traffic monitoring system as claimed in claim 1 wherein said user interface is configured to permit a user to generate inputs for roadway offset, lane width, number of lanes, and combinations thereof.

43. A traffic monitoring system as claimed in claim 1 wherein said user interface comprises a visual indicator configured to provide an indication of detection of a reflected laser pulse and a lane number corresponding to said detected pulse.

44. A traffic monitoring system as claimed in claim 1 wherein said non-intrusive lane monitor is configured to generate simulated contact switch signals from said reflected laser pulses and transmit said simulated contact switch signals to a host traffic counting unit.

45. A traffic monitoring system as claimed in claim 44 wherein said host is configured to determine vehicle classification and velocity from said simulated contact switch signals.

46. A traffic monitoring system as claimed in claim 1 wherein said lane monitor is configured to permit azimuth and elevation adjustment of each laser source.

47. A traffic monitoring system as claimed in claim 1 wherein said lane monitor comprises adjustable legs and an alignment scope configured to facilitate orientation of said first and second laser sources.

48. A traffic monitoring system as claimed in claim 1 wherein said lane monitor comprises a solar panel mounted thereto, said solar panel configured to generate electrical power for consumption by said lane monitor.

49. A traffic monitoring system comprising a non-intrusive lane monitor, said lane monitor comprising first and second laser channels, a user interface, and a programmable controller in communication with said first and second laser channels and said user interface, wherein:

said first laser channel comprises a first laser source and a first laser receiver;

said first laser source is configured to generate a first pulsed laser signal along a first laser axis;

said first laser receiver is configured to detect individual reflected laser pulses from said first pulsed laser signal;

said second laser channel comprises a second laser source and a second laser receiver;

said second laser source is configured to generate a second pulsed laser signal along a second laser axis;

said second laser receiver is configured to detect individual reflected laser pulses from said second pulsed laser signal;

said first laser axis is substantially parallel to said second laser axis;

said first and second laser axes lie substantially in a common horizontal plane;

said first laser axis is offset from said second laser axis in said common horizontal plane by a laser channel offset distance x; and

said programmable controller is configured to generate said first and second laser signals at a pulse repetition frequency PRF of at least about;

$\mathrm{PRF}\approx <br><br>\left(\frac{v}{\mathrm{px}}\right)$

where v corresponds to an expected average target speed, x corresponds to the channel offset distance and p corresponds to the desired percent precision in the speed determination.

50. A traffic monitoring system comprising a non-intrusive lane monitor, said lane monitor comprising at least one laser channel, a user interface, and a programmable controller in communication with said laser channel and said user interface, wherein:

said laser channel comprises a laser source and a laser receiver;

said laser source is configured to generate a pulsed laser signal along a laser axis;

said laser receiver is configured to detect individual reflected laser pulses from said pulsed laser signal;

said laser source is configured to generate pulsed laser signals having a cross sectional beam profile characterized by a minor axis of divergence and a major axis of divergence; and

said laser source is configured such that said minor axis of divergence lies in a substantially vertical plane said major axis of divergence lies in a substantially horizontal plane.

51. A traffic monitoring system as claimed in claim 50 wherein said first and second laser sources are configured to:

generate pulsed laser signals along a horizontal plane; and

generate pulsed laser signals characterized by cross-sectional profiles defining substantially vertical edges.

52. A traffic monitoring system comprising a non-intrusive lane monitor, said lane monitor comprising at least one laser channel, a user interface, and a programmable controller in communication with said laser channel and said user interface, wherein:

said laser channel comprises a laser source and a laser receiver;

said laser source is configured to generate a pulsed laser signal along a laser axis;

said laser receiver is configured to detect individual reflected laser pulses from said pulsed laser signal; and

said programmable controller is configured to;

generate reflected laser pulse count corresponding to reflection of a pulsed laser signal from a target positioned along one of said laser axes, and

identify said reflected signal as a valid or invalid target by comparing said pulse count to a predetermined valid target count.

53. A traffic monitoring system comprising a non-intrusive lane monitor, said lane monitor comprising at least one laser channel, a user interface, and a programmable controller in communication with said laser channel and said user interface, wherein:

said laser channel comprises a laser source and a laser receiver;

said laser source is configured to generate a pulsed laser signal along a laser axis;

said laser receiver is configured to detect individual reflected laser pulses from said pulsed laser signal; and

said programmable controller is configured to generate said first and second laser signals at a pulse repetition frequency sufficient to generate a plurality of reflected pulses as less than 1 inches (2.5 cm) of a target moving at a speed v intercepts one of said pulsed laser signals, said speed v being at least about 55 mph (90 km/h).

54. A traffic monitoring system comprising a non-intrusive lane monitor, said lane monitor comprising at least one laser channel, at least one constant fraction discrimination circuit, a user interface, and a programmable controller in communication with said laser channel, said constant fraction discrimination circuit, and said user interface, wherein:

said laser channel comprises a laser source and a laser receiver;

said laser source is configured to generate a pulsed laser signal along a laser axis;

said laser receiver is configured to detect individual reflected laser pulses from said pulsed laser signal;

said laser receiver is in communication with said constant fraction discrimination circuit;

said constant fraction discrimination circuit is configured to account for differences in respective rise times of laser pulses reflected from surfaces of differing reflectivity at a common range; and

said constant fraction discrimination circuit is configured to combine a detected reflected signal pulse with a delayed, inverted replica to obtain a signal that is substantially independent of pulse amplitude.