Inductive loop sensor for traffic detection, and traffic monitoring apparatus and method using such a loop sensor

• US 6,337,640 B2
• Filed: 03/31/1999
• Issued: 01/08/2002
• Est. Priority Date: 03/31/1999
• Status: Expired due to Term

• Current Assignee: Neology Incorporated (OEP Technologie BV)
• Original Assignee: Diamond Consulting Services Limited
• Inventors: Lees, Robert Harper
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Tang, Son M.
• Application Number:
  US09/282,371
• Publication Number:
  US 20010050621A1
• Time in Patent Office: 1,014 Days
• Field of Search: 340/933, 340/931, 340/941, 340/935, 340/919, 200/85.R, 200/86.A, 200/86.R, 324/236, 324/238
• US Class Current: 340/933
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Abstract

An inductive loop sensor for detecting vehicles travelling along a lane of a roadway comprises a figure-of-eight conducting loop. The loop is arranged with its three segments transversely across the roadway to detect the wheels of vehicles travelling along the roadway. The length of the loop in the direction of travel along the roadway is less than 60 cms. Traffic monitoring apparatus energises the loops and detects the passage of vehicle wheels over the loops to provide for the classification of vehicles by axle count.

Claims

1. An inductive loop sensor for detecting vehicles travelling along a lane of a roadway, the sensor comprising a continuous conductive loop, the loop being configured to provide a central conducting segment and outer conducting segments spaced on opposite sides of said central segment, whereby an electric current in the loop flows in a first transverse direction along said central segment and in a second transverse direction opposite to said first transverse direction along each of said outer segments,

wherein said loop is aligned on said roadway lane so that said central and outer segments extend transverse to the traffic flow direction in said lane, the distance between the outer segments of the loop being not greater than 60 cms.

2. An inductive loop sensor as claimed in claim 1, wherein said loop has a width across the traffic flow direction of between about 100 and about 140 cms.

3. An inductive loop sensor as claimed in claim 2, wherein said width of the loop is about 120 cms.

4. An inductive loop sensor as claimed in claim 1, wherein said distance between the outer segments is about 45 cms.

5. An inductive loop sensor as claimed in claim 1, wherein said central segment is symmetrically located between said outer segments.

6. An inductive loop sensor as claimed in claim 1, wherein said loop is configured as a figure-of-eight.

7. An inductive loop sensor as claimed in claim 1, wherein said loop is configured as a pair of multiturn windings of opposite hand connected in series.

8. Traffic monitoring apparatus comprising at least a first inductive loop sensor, a generator to energise said first loop sensor with a detection signal, and a detector responsive to changes in the detection signals in the loop sensor to provide an indication of a vehicle crossing the loop sensor, wherein the loop sensor comprises a continuous conductive loop having a central conducting segment and outer conducting segments spaced on opposite sides of said central segment, whereby an electric current in the loop flows in a first transverse direction along said central segment and in a second transverse direction opposite to said first transverse direction along each of said outer segments,

wherein said loop is aligned on said roadway lane so that said central and outer segments extend transverse to the traffic flow direction in said lane, the distance between the outer segments of the loop being not greater than 60 cms.

9. Traffic monitoring apparatus as claimed in claim 8, further comprising a second said inductive loop sensor having the same form as said first sensor, said first and second sensors being aligned spaced apart one after the other along the roadway lane in the traffic flow direction, said generator adapted to energise both said first and second sensors with respective detection signals, and said detector being responsive to changes in said signals in each of the sensors to provide an indication of the direction of travel of a vehicle crossing the sensors.

10. Traffic monitoring apparatus as claimed in claim 9, wherein said first and second loop sensors have similar dimensions and neighbouring outer segments of the two loop sensors are spaced apart in the traffic flow direction by between about 15 cms and about 25 cms.

11. A method of counting the number of axles of vehicles travelling along a lane of roadway comprising,

installing on or in a surface of the roadway lane at least one inductive loop sensor in the form of a continuous conductive loop having a central conducting segment and outer conducting segments spaced on opposite sides of said central segment, whereby an electric current in the loop flows in a first transverse direction along said central segment and in a second transverse direction opposite to said first transverse direction along each of said outer segments,

wherein said loop is aligned on said roadway lane so that said central and outer segments are transverse to the traffic flow direction in said lane, the distance between the outer segments of the loop being not greater than about 60 cms.

energising said sensor with a detection signal to generate a magnetic field which extends above the surface of the roadway lane by not more than about 30 cms, and detecting changes in said detection signal corresponding to the passage of vehicle wheels over the loop.

12. A method as claimed in claim 11, wherein said distance between outer segments of the loop is about 45 cms, and the magnetic field extends above the surface by about 22 cms.

13. A method as claimed in claim 11, wherein said loop has a width across the traffic flow direction such as to detect the wheel or wheels of a vehicle only at one end of each vehicle axle and the level of change in said detection signal is used to indicate the number of wheels being detected simultaneously.