Advances in Inductive Loop Detectors for Stop Bar
Detection and Counting
Scott EvansVP of EngineeringEberle Design Inc
Detection SystemsITS America Annual Meeting & Expo
June 6, 2007, Palm Springs CA
050807
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Evolution
Invented in Mid 50’s… yes the “1950’s”.
Engineering Standards beginning in the early 80’s until present.
80’s & 90’s saw major developments in electronics, geometrics, and installation standards.
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Evolution
Mid 90’s to present day, loop detection is reliable, accurate, simple to engineer and install, and conforms to standards.
Many new capabilities over generally understood simple detection have become available.
Loops are an invasive technique and do require maintenance.
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What is new?
New enhanced digital electronic designs leading to very high reliability and near faultless performance
Robust – less reliance on loop quality
Diagnostics for simple field installation & troubleshooting
Advanced Count Algorithms
Loop detection works in poor weather and poor lighting conditions
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Sophisticated Capabilities
Advanced capabilities LCD Graphical Menu Driven User
Interface Built in tools to aid in correct setup Advanced uP based algorithms with
higher operating and sampling speeds Automatic environmental tracking Fewer components for reliability
Properly configured modern loop detectors can provide exceptional operation even when presented with adverse conditions or poorly maintained loop systems.
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Sophisticated Capabilities Built-in tools for simple installation & trouble shooting
Call Strength meter Frequency meter Frequency stability meter
Fault Monitoring Detect and report loop issues such as open, shorted, and
large change in inductance Communications
NTCIP TSS Object MIB Vehicle classification and identification via Signature
analysis Built-in Applications
Speed Trap Directional Logic 3rd Car Logic
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The Need For Traffic Data The NTOC recently published National Traffic
Signal Report Card gave an overall grade of D- with detection getting an F.
Cycle by cycle data has been shown to be an effective method of analyzing a signalized intersection with Measures of Effectiveness such as volume to capacity ratios, arrival type, and average vehicular delay.
Traffic counts form the basis of almost all work performed by transportation engineers and planners.
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Vehicle Counting at the Stop Bar Good traffic data is used in allocation of federal
transportation funds, used in planning and design of the transportation system, used in financial and tax assessment, and used in environmental assessment.
Traffic data at signalized intersections are used in a variety of planning and traffic operational analyses: site impact studies, level of service analysis, intersection design studies, signal retiming, etc.
The potential to extract traffic counts from existing signalized intersection loop detection provides a golden opportunity.
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Loop Detector Count Capabilities
What is a Counting Detector? A primary output provides the traditional
presence output indicating the detection zone is occupied.
A secondary output of the detector provides a pulse for each vehicle entering the detection zone.
Many loop configurations are supported, for example:
Single small loop (6 ft length) Single long loop (12 to 50 ft length) Multiple small loops in series (two to eight 6 ft)
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Loop Detector Stop Bar Counting Recent INDOT field studies of the EDI Oracle Loop Monitor
have demonstrated “truthed” loop detection errors less than 1%.
97.00%
98.00%
99.00%
100.00%
101.00%
102.00%
103.00%
12 Hour Sample
3 Loops
1 Loop
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Loop Detector Stop Bar Counting Shorter 15 minute bins reveal +/- 4% errors on raw count data
due primarily to lane violations.
90.00%
92.00%
94.00%
96.00%
98.00%
100.00%
102.00%
104.00%
106.00%
7:30 AM 7:45 AM 7:59 AM 8:15 AM 8:29 AM 8:44 AM 9:00 AM 9:15 AM 9:29 AM 9:44 AM 10:01 AM
0
50
100
150
200
250
300
Volume
3 Loops
1 Loop
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Stop Bar Counting Analysis
Poor lane discipline by drivers contributed far more overall error than actual detector issues.
Thus, lane design and loop placement become the primary factors when using modern counting style loop detectors, but very high accuracies can be obtained 24 hours a day, in good or bad weather.
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Loop Detector Stop Bar Counting
New Adaptive control algorithms depend on accurate and real-time vehicle data input.
365 days per year of data collection.
Many agencies develop and deploy advanced techniques to improve traffic flow…But suffer from a reliable method to gauge their effectiveness.
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In Summary
Sixty years of development has led to long term reliability, low cost, and precise results.
Developing traffic data from existing loop infrastructure is a golden opportunity.
Inductive Loops…Still the benchmark to which all others are
measured against.
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References
ITE Traffic Engineering Council TENC 103-02 Using Existing Loops at
Signalized Intersections for Counts TRB Paper 06-1143, 11/1/2005
Evaluation of Flow Based Traffic Signal Control Using Advanced Detection Concepts
ITE Traffic Detector Handbook 2nd Edition, 1997