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

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Thank You Some examples of advanced loop detectors

with counting capability:

www.EDItraffic.com