BACKGROUND ][ TESTING ][ CARE AND MAINTENANCE ][ APPENDIX A
APPENDIX B ][ APPENDIX C ][ APPENDIX D

Background

The National Visitor Use Monitoring (NVUM) study began in 1999, a project to collect and analyze information about the numbers of people (visitors) using National Forest System lands. The study, using a statistical-based sampling method, requires Forest Service employees to conduct random onsite samples of forest visitors (figure 1).

Electronic traffic counters installed at each sampling site collect counts throughout the sample day (24-hour period). Each sampling day includes collecting 6-hours of voluntary exit interviews (filling out questionnaires) of forest visitors as they leave the sample site. The resulting information generates total visitor count and visitor profile (or description) of visitors exiting the sample site.

Because sample days are randomly selected throughout the yearlong sample period, bias is minimized. The randomness of sample days result in non-discriminating samples which may include operating electronic traffic counters during adverse weather conditions (specifically, temperature extremes and adverse weather conditions).

Extreme cold and hot temperatures are known to affect the operation of electronic counters; resulting in questionable accuracy of the collected data or counts.

Because data obtained from electronic counters is one of two main components vital to the accuracy of the overall National Visitor Use Monitoring (NVUM) study, there is a need to verify the assumption that the data from counters is the true count for each sample site. For quality data that is defensible, we must know how the various counter types compare and document potential bias and variance in data obtained by each counter type.
Counters must be evaluated under a variety of conditions to determine the effects of environmental conditions (temperature, precipitation, paved and unpaved road surfaces) and activity type (pedestrian/vehicular traffic) measured. By identifying the specific field conditions for each type of counter and developing trouble shooting tips, the quality (or accuracy) of the collected (counter) data will be improved. The desired end product is to provide future NVUM personnel with a user’s key on how and when to use different types of traffic counters and under what field conditions. Knowledge of test results will aid in explaining the data already gathered and can be used to make adjustments (corrective factors) in the analysis of data.


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Figure 1— Conducting winter-use exit
interviews for theNVUM study

INTRODUCTION

This report documents the evaluation of electronic traffic counters used in the National Visitor Use Monitoring study. Electronic traffic counters are evaluated for their accuracy under adverse temperature conditions. Ability to accurately detect vehicles and pedestrians is part of this evaluation. Three types of electronic counters are evaluated: pneumatic, active-infrared, and inductive loop. These counters are described in APPENDIX A. The evaluation was conducted during the winter and summer of 2003.

TESTING

Before evaluating the different types of counters, it is necessary to first isolate the potential errors that may be caused by the equipment (limitations or malfunction) and those factors that can be attributed to human error (installation and operation).

Knowing how the counter works and the environmental conditions that it will be used in can significantly reduce the human caused error. Much of this information can be gained from the manufacturer’s operating manual.
To validate or clarify some of the operating specifications of the counters, static (controlled or bench tests) and dynamic (field demonstration tests) tests were conducted. The tests require mimicking, for the most part, practical field installations.

Static Tests
Extreme Temperatures Errors attributed to extreme temperatures affect the counter’s internal electronic components or the mechanical-physical operation of sensors (pneumatic hoses). Extremely cold and hot temperatures are known to temporarily affect the operation of liquid crystal displays (LCDs) and storage/discharge capacity of (battery) power sources. Cold temperature decreases the flexibility or responsiveness of pneumatic hose material, when used in detecting passing vehicles.

Road and Trail Surfaces Errors attributed to road and trail surfaces mainly affect pneumatic counters. The hardness of the ground surface affects the compressibility of pneumatic hoses.

Dynamic Tests
Errors attributed to activity types affect pneumatic hose and infrared counters. The counters response to speed variations (or movement) made by different activities (pedestrian compared to vehicular) introduces error.

The tests and evaluations conducted during winter verify environmental factors (cold temperature affects all types of counters and snow fall affects on infrared counters). Evaluating road and trail surfaces effects on (pneumatic) counters during winter presents minimal problems as the hardness of frozen unpaved roads are similar to paved conditions. However, as the snow pack accumulates over the hose such conditions will affect performance. An evaluation on activity types (effect of fast moving snowmobiles) on accuracy of infrared and inductive loop counters was conducted.

Extreme Cold Temperatures and Pneumatic Sensors
A test procedure (or field validation method) was developed for measuring the effects of cold temperature on pneumatic hoses and the ability of the hose to generate sufficient trigger pressure (figure 2 ) (see Appendix b). The test evaluated the effects of two hose materials (synthetic rubber and all natural rubber) and two lengths (25 foot and 50 foot). Based on manufacturer’s information and pre-calculated data, a minimum trigger pressure (for the counter) could only be estimated, due to variation in factors, such as ambient temperatures and amplification characteristics of the counter.






Figure 2— Test setup for evaluating pneumatic counter.

Observed response to counter operations (accuracy)
The subzero temperatures did not appear to affect the operation of the counter and its ability to store collected data, provided sufficient trigger pressures are generated by the hose (see explanation below). Though the display is not readily available to the operator, the display was self-restoring as ambient temperatures approached room temperature.

Observed responses to hose material
The data supports comments from northern latitude forests’ that temperature becomes a significant factor when using synthetic rubber hoses at sub-freezing temperatures. This (measured) finding validates current recommendations to use natural rubber material (hose) as the temperatures lower to below 15 degrees F.

Observed responses to hose length
Shortening the length of the hose (especially, natural rubber) validated increasing trigger pressure. The amount of increased pressure is proportional to the speed of the passing vehicle. The information displayed on the monitoring equipment (oscilloscope) illustrates a profile of the passing vehicle’s axle (figure 3). The time duration (width of each pulse wave) of the pulses are inversely proportional to the time (in milliseconds) each tire imprints or makes contact with the hose. A slower moving vehicle will have a longer contact over the hose, and the corresponding amplitude of the pressure generated is less.






Figure 3— View of a two axle-vehicle
passing over the pneumatic hose.










Precipitation
In the form of heavy snow shower activity, such events can affect operation of infrared counters. Field attempts to mimic a “whiteout” snow condition failed to conclusively determine this effect on infrared counters. However, it was observed that counters installed under trees would respond accordingly to clumps of snow falling from above.

CARE AND MAINTENANCE

All counters evaluated are developed for outdoor use.

Batteries are a common problem among all electronic counters and therefore a major maintenance issue. All counters have indicators that give some warning when batteries become weak. However, the effectiveness of such indicators is limited by the operator’s failure to monitor and take action on the battery condition before the batteries fully discharge (go dead). Counters used in humid environments can often develop corrosion if not periodically checked and terminals cleaned. This was especially true of the TrailMaster, and Questa counters. Batteries left in counters during long periods of storage, resulted in corrosion of terminals.

The K-Hill pneumatic counters have lithium batteries lasting about 3 to 5 years. The battery is not replaceable in the field and can create unsuspected problems for the operator. RECOMMEND working with manufacturers to resolve battery issues and express importance in future NVUM trainings.

Transport of counters was identified as another issue. Many counters returned to the cache show signs of excessive wear. The K-Hill pneumatic counters have a clear protective plastic to protect the LCD. These shields were often torn or removed by operators. RECOMMEND providing a practical carrier (padded case) to resolve transport issues and express importance in future NVUM trainings.

APPENDIX A

Types of Counters Evaluated
Active Infrared This type of counter is used for detecting any object large enough to break the (invisible) light beam, such as animals, humans, and vehicles. Active infrared counters are further divided into subtypes: retro-reflective and through-beam (figure A- 3).

Figure A-3—Active infrared counters: Cuesta’s retro-reflective (left) and TrailMaster’s through-beam (right).




Pneumatic This type of counter is used for detecting any wheeled-object, of sufficient weight to depress a rubber hose, such as a passing vehicle (figure A-4).





Figure A-4— K-Hill’s pneumatic road tube counter











Magnetic Field or Inductive Loop This type of counter is used for detecting any object with adequate mass of metallic material, such as transport vehicles (including all-terrain vehicles, motorcycles, snow mobiles, and bicycles) (figure A-5).

Figure A-5— Diamond Traffic’s inductive loop counter.













APPENDIX B

Measuring the Effects of Temperature on Pneumatic Traffic Counter Hose — Field Evaluation.

Purpose
As reported by field technicians, the accuracy (or operation) of the K-Hill, model KBA-II, pneumatic traffic counter has been questioned, specifically when using the traffic counter under extreme environmental temperatures. There is a need to validate if (and what) such extreme temperatures have on the accuracy of the K-Hill Counter’s operation. This field test is intended to evaluate the operation of the counter (under extreme temperatures) and to help isolate (identify) any problem that may exist in relationship to the counter’s external trigger setup (pressure hose). This test focuses on temperature’s effects on the hose (as a sensor to trigger the counter’s air switch).

Test Procedure
Synthetic rubber hose material:

1. Using the prescribed test set up (figure 1) determine (or validate) the minimum pressure required to trigger the counter. Record counter’s display change (on traffic counter).
   
2. Install the test set up on a paved surface. Record the ambient ground temperature for the test period.
   
3. Run a vehicle over the hose at a prescribed speed of 25-30 mph and record counter’s display change and hose pressure generated (from transducer). Repeat ten times at each temperature to measure consistency in counter’s response and generated hose pressure.
   
4. Repeat Step 3 at different temperatures. Record test information on tables provided.*

Natural rubber hose material:

1. Using the prescribed test set up (figure 1) determine (or validate) the minimum pressure required to trigger the counter. Record counter’s display change (on traffic counter).
   
2. Install the test set up on a paved surface. Record the ambient ground temperature for the test period.
   
3. Run a vehicle over the hose at a prescribed speed of 25-30 mph and record counter’s display change and hose pressure generated (from transducer). Repeat ten times at each temperature to measure consistency in counter’s response and generated hose pressure.
   
4. Repeat Step 3 at different temperatures. Record test information on tables provided.*

* The KBA-II detects vehicle axles, each axle is a half count. Therefore, two generated pulses of air pressure is required to Record counter’s display a count of one vehicle.




Figure 1- Sketch of test apparatus.


EQUIPMENT:

Counter used and model: K-Hill Signal Co., KBA-II
Counter Serial Number: 2-163 (synthetic hose) & 2-355 (natural rubber hose)
Pressure Transducer Model: Z/0761-02ZG (15 psi)
Other Equipment: (specify model and serial number)
Oscilloscope (Tektronix, model TDS224)

Minimum pressure required to trigger a change in counter Record counter’s display:
Output to monitor/scope
________not determined_______ p.s.i.


Type of Hose (specify synthetic or natural rubber): synthetic
Ambient air temperature: minus 1.5°F     Hose length: 50 ft.

* display information not clearly visible.

Type of Hose (specify synthetic or natural rubber): synthetic
Ambient air temperature: 6.5°F Hose length: 25 ft.

Type of Hose (specify synthetic or natural rubber): natural rubber
Ambient air temperature: 12°F Hose length: 50 ft.

Type of Hose (specify synthetic or natural rubber): natural rubber
Ambient air temperature: 13.6°F Hose length: 25 ft.

APPENDIX C

Temperature Test

Purpose
To determine effect of extreme ambient temperature on Liquid Crystal Display operation.

Test Procedure
Place counters in environmental chamber and position counters so display is visible through chamber viewing window.
Set chamber temperature to desired temperature and hold for ½ hour to allow counter to assimilate to each temperature setting.
At each setting, trigger the display (by swiping with a magnet extended into the portal at the side of the chamber.
Record observed changes (or response) in counter LCD window.

APENDIX D

Measuring the Effects (or Relationship) of vehicle speed on Pneumatic Traffic Counter

Purpose
As reported by field technicians, the accuracy (or operation) of the K-Hill, model KBA-II, pneumatic traffic counter has been questioned, specifically when installing the traffic counter in developed campground where vehicle speeds are relatively slower than highway speeds. There is a need to validate if (and what) problems vehicle speeds have on the accuracy of the K-Hill Counter’s operation. This field test is intended to evaluate the operation of the counter (under varying vehicle speeds) and to help isolate (identify) any problem that may contribute to inaccuracies. This test focuses on relationship of vehicle speed and the generated triggers pressure at the output of the pneumatic (synthetic or rubber) hose.

Test Procedure

1. 1. Install the prescribed test set up (figure 1) on a paved (solid asphalt) surface. Record and monitor the ambient temperature during the test period.
   
2. 2. Determine the minimum pressure required to trigger the traffic counter by slowly driving the vehicle’s tires over the hose until the traffic counter displays a count.
   
3. 3. Drive a vehicle (mini van) over the hose at prescribed speeds of ≤ 5, ≥ 5, 10, 15, 20, and 25-30 mph. Record counter’s display change and hose pressure generated (as measured by transducer and oscilloscope). Make five vehicle passes at each speed to verify consistency in counter’s response.
   
4. 4. Repeat Step 3 at different vehicle speeds. Record test information on tables provided.*

* The KBA-II detects vehicle axles, each axle is a half count. Therefore, two generated pulses of air pressure is required to record counter’s display or a count of one event.



Figure 1- Sketch of test apparatus.


EQUIPMENT:
Counter used and model: K-Hill Signal Co., KBA-II
Counter Serial Number: 2-163 (synthetic hose) & 2-355 (natural rubber hose)
Pressure Transducer Model: Z/0761-02ZG (15 psi)
Other Equipment: (specify model and serial number)
Oscilloscope (Tektronix, model TDS224)

Minimum pressure required to trigger a change in counter Record counter’s display:
Output to monitor/scope
_______N/A________ p.s.i.

Type of Hose (specify synthetic or natural rubber): synthetic
Ambient air temperature: 72.2°F Hose length: 50 ft.

Ambient air temperature: 72°F     Hose length: 50 ft.

Ambient air temperature: 72°F     Hose length: 50 ft.

Ambient air temperature: 72°F     Hose length: 50 ft.

Ambient air temperature: 72°F     Hose length: 50 ft.

Ambient air temperature: 72°F     Hose length: 50 ft.

ACKNOWLEDGEMENT

The author wishes to thank Ted Etter for providing electronic support and technical review, Ken Hughes, Bill Kilroy, and Cassandra Weiss for their participation in test trials.