Traffic Detection Systems CEE 320 Anne Goodchild

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

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

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.

Why Is Traffic Detection Important?

Why Is Traffic Detection Important? Freeway Monitoring

Why Is Traffic Detection Important? Actuated Signal Control

Why Is Traffic Detection Important? Ramp Meter Control

Why Is Traffic Detection Important? Road Discipline Enforcement

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

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

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

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.

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)

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.

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

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

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

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

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)

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

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

Inductance Loop Detectors

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.

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

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).

Inductance Loop Detectors

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

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

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

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.

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

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

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

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.

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.

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.

A Use Example: Ramp Metering

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

Example: SR 520

What is the Difference?

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. http://www.calccit.org/itsdecision Wang, Y. (2004). CEE 599F, Advanced Traffic Detection Systems Course Pak. Civil and Environmental Engineering, University of Washington.