1. Traffic Detection Systems
CEE 320 Anne Goodchild

2. Outline What are traffic detectors? Traffic detector importance
Detector types
Use Example

3. What Are Traffic Detectors?
Traffic detectors are the devices that are used for detecting vehicles, bicycles, and pedestrians.
Experience at signalized intersections.

4. Traffic Detection Systems Structure
Detector
Processor/Controller
Storage
Different types of traffic detectors have different components. In general, it is comprised of detector, processor/controller, and storage media.

5. Why Is Traffic Detection Important?

6. Why Is Traffic Detection Important?
Freeway Monitoring

7. Why Is Traffic Detection Important?
Actuated Signal Control

8. Why Is Traffic Detection Important?
Ramp Meter Control

9. Why Is Traffic Detection Important?
Road Discipline Enforcement

10. Why Is Traffic Detection Important?
This map shows the Houston Transtar real-time traffic management system. Dynamic traffic assignment to emergency vehicles can significantly shorten travel times for emergency responses.
Dynamic Traffic Assignment

11. Why Is Traffic Detection Important?! !
ATIS
E-Message Sign
In summary, quality real-time data are fundamental to modern traffic control and management. A major source for such real-time traffic data is traffic detection systems.
Control Center
Quality Data

12. Traffic Detector Types
Inductive loops
Video
Microwave
Infrared
Acoustic
Radar
Magnetic
Radio frequency
Global positioning system (GPS)

13. Share of Detector Types at new ATMS Sites
Loop detectors still dominate the installations. This is probably because loops have been commodity-priced while the alternative detectors have not due to the short history of these detectors. As growing demand stimulates production, the per-unit cost of the most promising alternative detectors will begin to fall.

14. Popular Traffic Detector Types
Inductive Loop Detection System
Video Image Processing (VIP) System
Microwave Radar Based Traffic Detection System
GPS-Based Vehicle Tracking System
Acoustic Traffic Detection System
Infrared Traffic Detection System
Magnetic Traffic Detection System
Inductive loops
Video Image Processors (VIPs)

15. Popular Traffic Detector Types
(text from EIS also)
The RTMS requires no maintenance and was proven to be the only multi-zone traffic detector unaffected by any type of weather. The RTMS design has been proven to maintain accurate detection on any road surface type - even gravel roads, in tunnels and on steel bridges, in heavy snow, driving rain, strong winds and scorching desert sunlight. Its installation does not require road closures and its world-wide proven MTBF of 15 years cast it by far as the detector with lowest cost of ownership.
The RTMS is a miniature radar operating in either of two microwave bands, employing the FMCW (Frequency Modulated Continuous Wave) principle. It transmits a low-power microwave signal of constantly varying frequency in a fixed fan-shaped beam. The beam "paints" a long elliptical footprint on the road surface. Any non-background targets will reflect the signal back to the RTMS where the targets are detected and their range measured.
The RTMS range measurement resolution of 2 metres (7 ft.) allows the "slicing" of the footprint ellipse into 32 range-slices. The user can define a number (1 - 8) of detection zones, each consisting of one or more range slices.
The RTMS internal microcomputer controls in realtime 8 opto-isolator relays corresponding to the detection zones. Relay contacts are closed when a target is present within the respective detection zone. The contact-pairs can be connected directly to traffic controllers. In addition, short-term statistical data on each zone are accumulated and transmitted by the RTMS via its serial port. Typically, every 30 to 300 seconds a message containing the Volume, Occupancy, Average Speed and Classification by length data in each detection zone is transmitted.
The long microwave wavelength and the range-measurement capability make the RTMS immune to all weather effects and to most occlusion situations allowing vehicles hidden behind other vehicles to be detected, as shown in the diagram
Some acoustic detectors cover five lanes. There are both active and passive acoustic detectors available on the market.
Remote Traffic Microwave Sensor (RTMS)
Photos and picture from Electronic Integrated Systems, Inc.

16. Popular Traffic Detector Types
IR sensors detect the changes of temperature due to vehicle presence. Magnetic sensors transform changes in magnetic field intensity into inductance changes that can be sensed by vehicle detectors such as the 3M™ Canoga™ Vehicle Detector.
Magnetic Sensors
Infrared Sensors

17. Popular Traffic Detector Types
Radio Frequency Tag (RF Tag) can be used for Transit Signal Priority (TSP) and Signal Preemption systems.
Radio Frequency Tag

18. Popular Traffic Detector Types
ASIM TT 298: Doppler RADAR, ultrasonic, passive infrared.
Demo avi for this sensor is available.
Volume, classification, speed, occupancy, queue detection, wrong-way

19. Popular Traffic Detector Types
ASIM TT 298: Doppler RADAR, ultrasonic, passive infrared.
Demo avi for this sensor is available.

20. Popular Traffic Detector Types
Intersection Control
Traffic Data Acquisition
Demo avi for this sensor is available.
= infrared (counting)
= ultrasonic (vehicle height)
= microwave doppler radar (speed)

21. Popular Traffic Detector Types
A GPS data logger can be used to collect a vehicle’s position data periodically. Typically, a GPS data logger comprises of three parts: data storage media, GPS receivers, and power supply devices. It is small and affordable (about $300 in 2004).
GPS-Based Tracking Systems

22. Inductance Loop Detectors
Most popular
Photos from Never
Fail Loop Systems, Inc.

23. Inductance Loop Detectors

24. Inductance Loop Detectors
A Schematic Diagram
The inductance seen at the loop terminals is modified by the capacitance and results in an inductance which increases with increased operating frequency.

25. Loop Detector Signatures
Bigger bump is engine and front axle, smaller bump is rear axle

26. Inductance Loop Detectors
Traffic Control Cabinet
Lead-In Cable
DEUs
Field Component
Loop wires
Pull Box
Components:
One or more turns of insulated loop wire wound in a shallow slot sawed in the pavement.
A lead-in cable from the curbside pull box to the controller cabinet.
A detector electronic unit housed in the controller cabinet (can control upwards of 40 loops, but usually less in practice).

27. Inductance Loop Detectors

28. Inductance Loop Detectors
Loop inductance decreases when a car is on top of it.
Inductance
T = ton
ton
T = toff
toff
Time

29. Inductance Loop Detectors
Time
Inductance
High
low Tn
Tn+1
tn1
tn2
tn3
Single loop measurements?
Single loops can measure:
Occupancy (O): % of time loop is occupied per interval
Volume (N): vehicles per interval

30. Dual Loop Detector
Formed by two consecutive single loop detectors placed a short distance apart
lloop
ldist

31. Dual Loop Detectors Dual loop measurements T = t2 T = t1 ldist lloop
oti = on-time for loop detector i
Measured vehicle lengths are used to classify vehicles into different categories, such as long and short.

32. Inductance Loop Detectors
Loops
Station
cabinet
TSMC
measured data
per 20 sec.
real time
measurements
queried
20 sec data
(e.g. 0:00:00 3, 0.98
0:00:20 2, 0.65)
User
Only 20 sec aggregated data are available from TSMC

33. Can We Get Speed from a Single Loop?
Perhaps… s =
speed (ft/sec)
EVL
effective vehicle length (ft) to
occupancy time (s)
EVL ~ vehicle length + detector length

34. Can We Get Speed from a Single Loop?
Using typical traffic data s =
speed (miles/hr) N
number of vehicles in the observation interval T
observation interval (s) O
percentage of time the loop is occupied by vehicles during the observation interval (occupancy) g
speed estimation parameter
100 converts percent to decimal

35. Inductance Loop Detectors
Using single loop detector measurements, traffic speed can be estimated using the speed calculation algorithms. This slide shows a snap shot of a real-time traffic information system developed by the STAR Lab.

36. Video Image Processors
A snapshot of video detector set up. Currently, most new detector types, including VIP and RTMS, are compatible with loop detector output.

37. Video Image Processors
Since VIPs provide more information than just high or low voltage, they can be used for more advanced applications. For example, the STAR Lab developed an algorithm for detecting signal control cycle failures using VIP image sequences. Red-signal enforcement systems based on video images have been available since 1990s.

38. A Use Example: Ramp Metering

39. Diagram from ITS Decision website
Ramp Meter Schematic
Diagram from ITS Decision website

40. Example: SR 520

41. What is the Difference?

42. Primary References
Cosgrove, C. and Cutchin, C. (2003). ITS Decision. Website hosted by the California Center for Innovative Transportation at the University of California and Berkeley and Caltrans.
Wang, Y. (2004). CEE 599F, Advanced Traffic Detection Systems Course Pak. Civil and Environmental Engineering, University of Washington.