1. Advances in Inductive Loop Detectors for Stop Bar Detection and Counting
Scott Evans
VP of Engineering
Eberle Design Inc
Detection Systems ITS America Annual Meeting & Expo June 6, 2007, Palm Springs CA
050807

2. 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.
I intend to make two main points:
State of the Art improvements of Inductive Loop Detectors
Solution for developing traffic counts at the intersection using existing infrastructure
Like Tiger’s Oldsmobile, This is not “your Dad’s detector anymore”

3. 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.
Inductive loop detectors are a mature product.
We are currently in the 3rd Generation of the product cycle
Initial development of analog loop amplifiers and in-road loop design
Development of commodity type products
Advanced product development beyond “just making them work”.
Challenges still exist in maintaining the physical loop sensor in the roadway. Preformed loops provide a very rugged product to address some of the reliability issues.

4. 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
Powerful microprocessor based designs (>5 MIPs)

5. 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.
Major improvements in User Interface – LCD menu driven
Provides tools for ensuring correct installation tailored to field conditions.
Set it up right to avoid problems, not come back and fix them later.
Relatively simple in mechanical / electrical complexity -> high reliability
Much work has been done of late to eliminate typical problems such as lock-up, cross-talk, and noise immunity.

6. 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
The key is to install and configure correctly
Have confidence that the settings are consistent with the installation and not just “it detects”
When problems do occur, provide the technician with tools to diagnose and remedy.
NTCIP, TSS object MIB
Lead in to counting application here….

7. 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.
If the FHWA was the Father of this industry, we would all be grounded.
Deploying advanced systems and then quantifying results is difficult at best without data and measurement capabilities.
Advanced systems need accurate data input.

8. 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.
Need for data is hopefully just “Preaching to the choir”
The infrastructure is already in place in many cases to gather important data.

9. 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)
It performs the basic presence mode operation to provide service to actuated approaches.
Adds a secondary output to count vehicles as they pass through the detection zone, even when more than one vehicle occupies the zone.
Adaptable to most loop configurations.
Trade-off in design related to both loop geometry and placement in the roadway.
Final choice of design may prioritize the main function of the loop to zone size, maintenance, or counting.

10. Loop Detector Stop Bar Counting
Recent INDOT field studies of the EDI Oracle Loop Monitor have demonstrated “truthed” loop detection errors less than 1%.
Field studies demonstrate errors due to the detector itself are extremely small.
Plot shows long term 12 hr results, 2286 vehicles from 2006 Purdue study.
A study from as recently as 2001 by NCDOT showed typical errors from 5-18%. This is now “old” technology!
Lane placement and design were most important factors.
Accuracy required very much depends on the application. Cycle by cycle data the most demanding.
The current technology provides a solution to collect accurate count data from existing infrastructure.

11. Loop Detector Stop Bar Counting
Shorter 15 minute bins reveal +/- 4% errors on raw count data due primarily to lane violations.
Three loop series is a detection zone of 36 ft
One loop series is a detection zone of 6 ft
Because of the smaller sample sizes, the error rate is higher. Video replay “truthing” reveals the error rate results primarily from lane violations and truck / trailer traffic.

12. 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.

13. 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.
To move forward with adaptive and predictive algorithms, accurate and time relevant traffic data will be needed.
Even simple timing changes are difficult without traffic data to analyze. Once implemented, grading the results again needs the traffic data.

14. Still the benchmark to which all others are measured against.
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.
Inductive Loop Detectors are a mature product technology.
State-of-the-art enhancements are providing applications impossible until recently, such as intersection traffic data.
The loop infrastructure across the country is huge, and extracting count data from the “stop bar” detectors presents a golden opportunity at little extra cost.

15. References ITE Traffic Engineering Council
TENC Using Existing Loops at Signalized Intersections for Counts
TRB Paper , 11/1/2005
Evaluation of Flow Based Traffic Signal Control Using Advanced Detection Concepts
ITE Traffic Detector Handbook
2nd Edition, 1997
TENC provides detailed analysis of various considerations for obtaining counts at the stop bar.

16. Thank You
Some examples of advanced loop detectors with counting capability:
Eberle Design Inc.
3819 East LaSalle Street
Phoenix, AZ
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