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"State-of-the-Art" Report on Non-Traditional Traffic Counting Methods
Final Report 503
Prepared by: Sherry L. Skszek 505 N. Tanque Verde Loop Rd. Tucson, AZ 85748
October 2001
Prepared for: Arizona Department of Transportation 206 South 17th Avenue Phoenix, Arizona 85007 in cooperation with U.S. Department of Transportation Federal Highway Administration
The contents of the report reflect the views of the authors
Technical Report Documentation Page
TABLE OF CONTENTS
APPENDIX A: SURVEY INSTRUMENT APPENDIX B: TRAFFIC COUNTING SURVEY RESULTS APPENDIX C: BIBLIOGRAPHY APPENDIX D: WEBSITE BIBLIOGRAPHY APPENDIX E: MANUFACTURER LIST APPENDIX F: MNDOT REPORT CONCLUSIONS
LIST OF FIGURES Figure 1. Product Classification
LIST OF TABLES Table 1. Manufacturer List Table 2. Product List Table 3. Freeway Detector Annualized Per-Lane Cost Comparison Table 4. Limitations of the Technology Table 5. Application Guide for Detector Selection on Freeways Table 6. State Departments of Transportation Table 7. Level of Satisfaction by State Table 8. Usage and Average Level of Satisfaction Table 9. Disadvantages Reported by Technology Table 10. Method of Data Collection Table 11. Frequency of Method Use Table 12. Device Manufacturers Table 13. Qualitative Assessment of Best Performing Technologies for Gathering Specific Data Table 14. Devices Evaluated in MnDOT Study Table B1. Level of Satisfaction Table B2. Disadvantages Reported Using Manual Observation Table B3. Disadvantages Reported Using Bending Plates Table B4. Disadvantages Reported Using Pneumatic Road Tubes Table B5. Disadvantages Reported Using Piezo-Electric Sensors Table B6. Disadvantages Reported Using Inductive Loops Table B7. Disadvantages Reported Using Passive Magnetic Devices Table B8. Disadvantages Reported Using Radar Table B9. Disadvantages Reported Using Passive Acoustic Devices Table B10. Disadvantages Reported Using Video Image Detection Table B11. Frequency of Method Use to Collect Count Data Table B12. Frequency of Method Use to Collect Speed Data Table B13. Frequency of Method Use to Collect Weight Data Table B14. Frequency of Method Use to Collect Classification Data Table B15. Traffic Data Reported Using Manual Observation Table B16. Traffic Data Reported Using Bending Plates Table B17. Traffic Data Reported Using Pneumatic Road Tubes Table B18. Traffic Data Reported Using Piezo-Electric Sensors Table B19. Traffic Data Reported Using Inductive Loops Table B20. Traffic Data Reported Using Passive Magnetic Devices Table B21. Traffic Data Reported Using Radar Table B22. Traffic Data Reported Using Passive Acoustic Devices Table B23. Traffic Data Reported Using Video Image Detection Table B24. Manufacturers Utilized by Each State
Any State using traffic data for the apportionment or allocation of Federal funds must have a traffic monitoring system that meets Federal Highway Administration requirements. As part of a traffic monitoring program, States are required to gather vehicle count, classification, and weight data. Since participation in federally funded programs is essential to the integrity of a State’s highway systems, the accurate, efficient collection of traffic data becomes a critical component of transportation infrastructure management. This report looks at the state-of-the-art of non-traditional traffic counting methods to facilitate informed decision making regarding changes to existing practices. The report is comprised of three sections—an evaluation of current technology, a survey of State Departments of Transportation (DOT) traffic counting practices, and a literature review. The evaluation of current technology was conducted through interviews with over fifty manufacturers of traffic counting devices as well as a review of the literature on existing technology. The survey of State DOTs involved sending a two-page survey to each of the fifty agencies requesting information on level of satisfaction with devices currently in use, disadvantages of the technology, manufacturer information, and data gathered using each device. Lastly, a literature review of new technology was conducted to uncover new trends in traffic counting practices. Two main categories were identified—intrusive and non-intrusive data collection devices. Intrusive devices are those that involve placement of the sensor technology on top of or into the lane of traffic being monitored. Conversely, non-intrusive devices do not interfere with traffic flow either during installation or operation. The information gathered was differentiated into one of these two categories. The type of traffic data collection devices available on the market has changed little in the past decade. The same thirteen technologies are still being utilized by State, county, city, and metropolitan organizations responsible for traffic monitoring operations. However, the devices have evolved as their use has come under greater scrutiny with the recent focus on "intelligent transportation systems." Such non-traditional technology as video image detection, Doppler microwave, passive magnetic, passive acoustic, active and passive ultrasonic, and active and passive infrared technology now are being used with increased frequency for data collection and traffic management. The second section of the report deals with the Arizona Department of Transportation Traffic Counting Survey. All fifty States submitted responses to the survey. The results showed that less than half of all States are using non-intrusive (non-traditional) methods for gathering traffic data. Although the level of satisfaction with intrusive devices is relatively high, there is pressure to find methods of data collection that will keep traffic counting professionals out of the lanes of traffic. A few manufacturers were identified as leaders in the industry with current technology. It is yet to be seen if they will continue to lead as the move toward non-intrusive technologies begins to dominate the marketplace. The last section of the report contains a review of the literature on emerging technology. There is little in the way of new devices; however, the information uncovered relates to improvements in existing technology. Manufacturers are looking toward "signatures" to improve on the accuracy of vehicle classification. This pattern matching technology is being used with inductive loops and passive acoustic devices to improve on current technology. Neural network software is able to use the unique characteristics of a vehicle designated as a "signature" to more accurately classify a vehicle even beyond the Federal Highway Administration’s thirteen classes. Piezo-electric sensors also have evolved with advances in the material used as the force transducer. Quartz materials, being highly insulated, are being employed to improve on the collection of weight-in-motion data. New technology is followed by a review of recent research on evaluations of non-intrusive traffic data collection devices. Studies have been conducted by organizations involved the transportation industry including the Federal Highway Administration, State DOTs, universities, and private industry in an effort to determine if the newer non-intrusive technologies are capable of more cost-effectively collecting reliable traffic data. The studies show promising results from the non-intrusive technologies but continued research and development is needed to provide appropriate documentation to convince traffic counting professional that a transition to new technology is in their best interest. In summary, the collection of accurate traffic data in a cost-effective manner is essential to the allocation of scarce resources needed to support an aging infrastructure. The pressure to move the industry forward will provide the impetus for manufacturers to continue to develop the newer non-intrusive technologies and show they can meet the stringent requirements set forth by today’s traffic counting professionals.
The purpose of this research project is to examine current state-of-the-art non-traditional traffic counting practices throughout the transportation industry. This information was gathered through interviews with manufacturers of existing technology and review of the literature. In addition, traffic counting professionals from state departments of transportation were surveyed to obtain information on their current practices and level of satisfaction with the systems they have in place. This report summarizes the information gathered and will be used during the decision making process involving the feasibility and cost effectiveness of improvements in Arizona Department of Transportation’s current traffic counting practices. The Federal-Aid Policy Guide established by the Federal Highway Administration mandates "requirements for development, establishment, implementation, and continued operation of a traffic monitoring system for highways and public transportation facilities and equipment in each State." Subchapter F of the Federal-Aid Policy Guide outlines general requirements for compliance with this policy. States must comply with these requirements when traffic data generated by the state are used for the following purposes:
A State’s traffic monitoring procedures also apply to the "activities of local governments and other public or private non-State government entities collecting highway traffic data within the State" if the data are used for any of the purposes described above. Since participation in federally-funded programs is essential to the integrity of a State’s highway systems, the accurate, efficient collection of traffic data becomes a critical component of transportation infrastructure management. As part of a traffic monitoring system, States are required to record traffic volumes, vehicle classification, and vehicle weight data. This information is collected at short-term counting stations and at long-term, continuous counting stations. Short-term counts are then adjusted for seasonal, day-of-the-week, and other factors as assessed at continuous count stations to provide estimates of traffic patterns throughout the State’s highway infrastructure. This information provides documentation to ensure the State receives appropriate levels of federal funding to maintain or expand its highway system. It also aids in the design of highway improvement projects. Decisions made regarding upgrades to traffic counting practices should be based on accurate, up-to-date information. This report summarizes the current state-of-the-art in traffic enumeration devices to facilitate this decision making process. This report is comprised of three components—an evaluation of current technology, a literature review, and a survey of State Department of Transportation (DOT) practices. The first section summarizes information supplied by manufacturers of devices used to collect count, speed, classification, and/or weight-in-motion data. Each manufacturer was asked to provide information regarding sensor technology, applications, classification algorithm, lane-monitoring capability, price, installation requirements, telemetry, calibration, power requirements, temperature requirements, and limitations of the system for each product. The second section contains the results of the Traffic Counting Survey circulated to the fifty State DOTs. Results were compiled in an Access database and summarized into tables for display in this report. The survey is included as Appendix A. Individual results from each state are included in Appendix B. The last section contains information gathered through a review of books, journals, Internet websites, and interviews with traffic counting professionals. Due to rapid advances in the area of traffic management, the review was limited to information from the past five years. A bibliography of relevant journal articles and websites dealing with traffic counting devices and transportation technology is included as Appendices C and D. 2.0 CURRENT TRAFFIC DATA COLLECTION TECHNOLOGY There are two main categories into which equipment for collecting traffic data can be placed—intrusive and non-intrusive devices. Intrusive (traditional) counting devices are those that involve placement of the sensor technology on top of or into the lane of traffic being monitored. They represent the most common devices used today including inductive loops, piezo-electric sensors and pneumatic rubber road tubes. Conversely, non-intrusive (non-traditional) counting devices such as passive acoustic and video image detection do not interfere with traffic flow either during installation or operation. Within these two broad categories, thirteen different technologies were identified for classifying devices used for recording traffic data. The collection of count, speed, class, and weight-in-motion (WIM) data are the focus for this report.
Figure 1. Product Classification A definition of each category, as used for purposes of this report, is listed below INTRUSIVE DEVICES Bending plate technology is most frequently used for collecting weight-in-motion data. The device typically consists of a weigh pad attached to a metal frame installed into the travel lane. A vehicle passes over the metal frame causing it to slightly "bend." Strain gauge weighing elements measure the strain on the metal plate induced by the vehicle passing over it. This yields a weight based on wheel/axle loads on each of two scales installed in a lane. The devices also is used to obtain classification and speed data. A pneumatic road tube is a hollow rubber tube placed across the roadway that is used to detect vehicles by the change in air pressure generated when a vehicle tire passes over the tube. A device attached to the road tubes is placed at the roadside to record the change in pressure as a vehicle axle. Axle counts can be converted to count, speed, and/or classification depending on how the road tube configuration is structured. Piezo-electric sensors are mounted in a groove that is cut into the roadway surface within the traffic lane. The sensors gather data by converting mechanical energy into electrical energy. Mechanical deformation of the piezo-electric material causes a change in the surface charge density of the material so that a change in voltage appears between the electrodes. The amplitude and frequency of the signal is directly proportional to the degree of deformation. When the force of the vehicle axle is removed, the output voltage is of opposite polarity. The change in polarity results in an alternating output voltage. This change in voltage can be used to detect and record vehicle count and classification, weight-in-motion and speed. [1] An inductive loop is a wire embedded into or under the roadway in roughly a square configuration. The loop utilizes the principle that a magnetic field introduced near an electrical conductor causes an electrical current to be induced. In the case of traffic monitoring, a large metal vehicle acts as the magnetic field and the inductive loop as the electrical conductor. A device at the roadside records the signals generated. [2] NON-INTRUSIVE DEVICES Manual observation involves detection of vehicles with the human eye and hand recording count and/or classification information. Hand-held devices are available for on-site recording of information gathered by one or more individuals observing traffic. 2.1.6 Passive and Active Infrared Passive infrared devices detect the presence of vehicles by measuring the infrared energy radiating from the detection zone. A vehicle will always have a temperature contrast to the background environment. The infrared energy naturally emanating from the road surface is compared to the energy radiating when a vehicle is present. Since the roadway may generate either more or less radiation than a vehicle, the contrast in heat energy is detected. The possibility of interference with other devices is minimized because the technology is completely passive. Passive infrared detectors are typically mounted directly over the lane of traffic on a gantry, overpass or bridge or alternatively on a pole at the roadside. Active infrared devices emit a laser beam at the road surface and measure the time for the reflected signal to return to the device. When a vehicle moves into the path of the laser beam the time it takes for the signal to return is reduced. The reduction in time indicates the presence of a vehicle. The mounting position for active infrared detectors is more variable. The Autosense devices from Schwartz Electro-Optics, Inc. are mounted over the lane(s) of traffic to be monitored or in a side-fire mount perpendicular to the lane of traffic. There also are portable, devices that are placed roadside so the laser beams are directed parallel to the road surface across the lane of traffic. Both active and passive infrared devices can be used to record count, speed, and classification data. Passive magnetic devices detect the disruption in the earth’s natural magnetic field caused by the movement of a vehicle through the detection area. In order to detect this change the device must be relatively close to the vehicles. This limits most applications to installation under or on top of the pavement, although some testing has been done with side fire devices in locations where they can be mounted within a few feet of the roadway. Magnetic sensors can be used to collect count, speed, and classification data. 2.1.8 Microwave - Doppler/Radar Doppler microwave detection devices transmit a continuous signal of low-energy microwave radiation at a target area on the pavement and then analyze the signal reflected back. The detector registers a change in the frequency of waves occurring when the microwave source and the vehicle are in motion relative to one another. According to the Doppler principle, when a moving object reflects the radar beam emitted from the detector, the frequency of the reflected wave is changed proportionally to the speed of the reflecting object. This allows the device to detect moving vehicles and determine their speed. The only sensors identified using Doppler microwave are produced by Microwave Sensors, Inc. and are used primarily as a detection device designed to trigger operation of a traffic controller. In this capacity, they are placed in an overhead mounting position. Radar (radio detecting and ranging) is capable of detecting distant objects and determining their position and speed of movement. With vehicle detection, a device directs high frequency radio waves, either a pulsed, frequency-modulated or phase-modulated signal, at the roadway to determine the time delay of the return signal, thereby calculating the distance to the detected vehicle. Radar devices are capable of sensing the presence of stationary vehicles. They are insensitive to weather and provide day and night operation. The device is placed in a side-fire mount off the shoulder of the roadway. This technology is capable of recording count, speed, and classification data. 2.1.9 Ultrasonic and Passive Acoustic Ultrasonic devices emit pulses of ultrasonic sound energy and measure the time for the signal to return to the device. The sound energy hits a passing vehicle and is reflected back to the detection device. The return of the sound energy in less time than the normal road surface background is used to indicate the presence of a vehicle. Ultrasonic sensors are generally placed over the lane of traffic to be monitored. Passive acoustic devices utilize sound waves in a somewhat different manner. These systems consist of a series of microphones aimed at the traffic stream. The device detects the sound from a vehicle passing through the detection zone. It then compares the sound to a set of sonic signatures preprogrammed to identify various classes of vehicles. The primary source of sound is the noise generated by the contact between the tire and road surface. These devices are best used in a side fire position, pointed at the tire track in a lane of traffic to collect count, speed, and classification data. Video image detection devices use a microprocessor to analyze the video image input from a camera. Two techniques, trip line and tracking, are used to record traffic data. Trip line techniques monitor specific zones on the roadway to detect the presence of a vehicle. Video tracking techniques employ algorithms to identify and track vehicles as they pass through the field of view. Different manufacturers technology may employ one or both of these techniques. Optimal mounting position for video image detectors is directly over the lane(s) to be monitored with an unobstructed view of traffic. Side mounting is feasible but large vehicles may obstruct detection zones. The mounting height is related to the desired lane coverage, usually 35 to 60 feet above the roadway. Video detection devices are capable of recording count, speed, and classification data. 2.2 MANUFACTURERS OF TRAFFIC COUNTING DEVICES A list of manufacturers was compiled through an Internet search and by conversations with traffic counting professionals. Any manufacturer producing one or more devices for collection of count, speed, classification, and/or WIM data was considered. Many systems are "open systems" in that the sensors and data collection devices may be from different manufacturers. This is the case with most pneumatic rubber tube and inductive loop systems. In addition, the data collection devices employed by these systems may utilize more than one sensor type. For the most part, the more sophisticated the technology, the more likely the system will be a "closed" system. Table 1 contains manufacturers identified by this researcher who were cooperative in supplying detailed product information and were responsive to questions regarding their products. The devices are categorized by their sensor technology; however, the product listing is limited to the devices used to interpret data output from the sensors. Manufacturers producing only sensors and not data recording devices were excluded from Table 1. A more detailed listing that includes contact name, address, telephone number, e-mail address, and website information for each manufacturer is included as Appendix E.
Each manufacturer was contacted for product information for any device they distribute that is used to collect traffic count, speed, classification, and/or WIM data. The focus was on devices designed specifically for use in high speed, freeway applications. Devices used primarily for presence detection at intersections for traffic signal applications or on freeway entrance ramps for traffic management were not considered. Table 2 summarizes devices currently on the market including manufacturer name, sensor type, and data collected. Although the devices are listed by sensor type, the emphasis was on acquiring information about the data recording and interpretation equipment that is attached to the various sensors. The sensor type used with a particular piece of equipment may or may not be made by the manufacturer listed. As previously stated, there is a wide range of open and closed systems available. Devices used for recording information obtained by manual observation were not included. Some issues that should be considered when selecting a particular product include traffic conditions at the site to be monitored, type of data to be collected, installation requirements, weather conditions, lane coverage, cost, and maintenance requirements. These requirements can determine whether a particular traffic counting device can or will work acceptably. It also is highly desirable for a new system to be field tested at the site in question prior to purchase of the device. Detailed information including technical specifications and installation requirements for each product in Table 2 are summarized in a Microsoft Access database.
Key to Sensor Types:
General considerations addressed in the product database are reviewed below. The installation requirements for each device are based on the type of sensor technology with a few exceptions. Looking first at traditional "intrusive devices," all pneumatic road tube products identified require the sensor to be placed across the roadway and attached to a counting device that is placed along the roadside. Installation generally takes less than an hour but requires some intrusion into the flow of traffic. Placement of road tubes is easy, quick and requires minimal technical expertise. Bending plates are much more labor-intensive to install. They require fixing the device to the roadway so intrusion in the flow of traffic is necessary. Piezo-electric sensors can be placed across the road surface or imbedded in the roadway. Imbedding the sensor requires cutting into the asphalt or concrete surface. The counting device is placed at the roadside. Installation can take less than an hour if the sensors are on top of the road surface or can take up to two days if placed into the roadway. Similar to some piezo-applications, inductive loop devices require the sensor to be imbedded in the roadway with the counting device placed at the roadside or in a nearby traffic cabinet. Again, inductive loop installation can take up to two days and will require lane closures. The non-invasive, non-traditional technologies identified could be divided into three groups based on installation requirements. The video detection, passive infrared, and ultrasonic devices require mounting directly over the traffic lane(s) with an unobstructed view of the traffic being monitored. The optimal height is typically 35-45 feet. Two manufacturers indicated roadside mounting is permissible in the absence of an overhead structure; however, accuracy diminishes the further the device is from the most distant lane being monitored. Installation time was consistently given as two hours for system set-up with additional time dependent on the availability of a suitable mounting structure. In addition, the presence of a bucket truck and flag support maybe required dependent on the installation site. Two manufacturers were identified who produced passive magnetic devices for freeway data collection—3M and Nu-Metrics. This technology requires that it be installed close to the road surface. The 3M Canoga micro-loop system is placed under the lane of traffic in PVC tubing without disrupting the road surface. A conduit is installed using horizontal directional drilling, without digging a trench. Nu-Metrics offers three passive magnetic devices that are installed by placing the small portable devices on or in the roadway. This technology is typically categorized as non-intrusive; however, placement of the sensors in the line of traffic seems to contradict this premise. Another manufacturer of passive magnetic devices, Safetran Traffic Systems, produces the IVHS sensor. However, the manufacturer recommends the device for detecting vehicle presence rather than highway traffic counting and classification. The last group—radar, passive acoustic, and active infrared devices—are typically mounted roadside on an existing structure such as a street light or sign post. Sensor placement will impact how many lanes of traffic can be successfully monitored. The time required for installation is similar to the video detection devices. Set-up of the device takes about two hours if there is an existing roadside structure for mounting the sensor. The only exceptions identified were the Multi-Lane Monitoring System (MLMS) by Spectra-Research and the SafeCount by Peek Traffic. These devices are portable, active infrared systems placed on the ground 10 to 15 feet from the lanes of traffic to be monitored. Installation time is less than one hour. 2.4.2 Power and Temperature Requirements Power and temperature requirements for each of these devices did not seem to present limiting factors with respect to product selection. The majority of the devices that were placed free standing along the roadside were battery operated and offered several options related to battery size, solar power, and rechargeable varieties. It is likely that power requirements would be of most concern in remote areas where power sources are unavailable. In this case, short-term portable counting devices could be utilized. Most single channel permanent installations offered battery options but multi-channel devices require 120 VAC. The operating temperature ranges for all devices were on the average from –30° to +65° C (-22° to +149°F). The Nestor Traffic Vision was a rare exception with an operating range of only +10° to +35° C (+50° to +95° F). Temperatures would be problematic only in regions of the country where weather extremes are frequent occurrences. However, it is important to keep in mind that the manufacturer's reported operating ranges may not take into account "real world" factors. Although the device may perform well in a test environment, there are "real world" conditions that can cause a device to fail. For example, the high summer temperatures in Arizona can cause the asphalt to shove leading to failure of inductive loops. Manufacturers may be unaware of these issues or reluctant to share them with potential buyers. Consequently, it is prudent to contact actual users for their experience prior to purchasing a new device. Table B24 in Appendix B lists the manufacturers of traffic counting devices used by each state to assist in this process. Data retrieval techniques ranged in complexity from reading traffic counts from a visual display on the recording device to having the ability to remotely configure, perform diagnostics and extract data via modem, landlines or wireless connection. Most systems offer more than one option for data retrieval with the degree of flexibility dependent more on the data collection device rather than the sensor type. The number of data retrieval options available increases with the level of sophistication and complexity of the equipment. The pneumatic road tube, inductive loop, and piezo-electric sensor systems consistently offer roadside data retrieval using data cards or a laptop. A few low cost models that record strictly traffic counts offer visual displays so that a computer is not necessary. With non-intrusive technology, remote data retrieval is more typically available. The minimum requirement is a receiving computer, either laptop or PC, with an RS-232 serial communication port being the most common standard for data retrieval. The purchase of additional software or data modules will increase the available options but also increases the price of the system. In general, most manufacturers are willing to work with the end user to configure a system that fits their data collection and retrieval needs as well as budget. Price information was requested from all manufacturers. The prices quoted were very dependent on site parameters that would be unique to a particular installation. There also were many issues that varied between manufacturers as to what was or was not included with the product. Some variables included data analysis software, types of sensors, rack or shelf mount format, data storage capacity and optional modules for data retrieval or WIM. Consequently, it was difficult to obtain information that was comparable across product lines. In considering equipment cost, on the surface the prices for non-intrusive devices appear to be higher. But, this may not actually be the case. The Texas Transportation Institute (TTI) study addressed the issue of life-cycle cost in its report Evaluation of Some Existing Technologies for Vehicle Detection. In this study, inductive loops were compared to other non-intrusive detection systems in several districts throughout Texas representing different sized urban applications. The elements that were considered in the life-cycle cost of each device were installation cost, maintenance costs, traffic control, motorist delay and related excess fuel consumption, additional pavement maintenance costs, and costs related to increased crash rates during installation and maintenance of some detectors. Table 3, reproduced from the TTI study, shows the per-lane cost comparison. It must be kept in mind that the TTI project summary covers the period from September 1996 to August 1999 so the price information is not current. However, it is possible to garner a relative cost comparison between the four different technologies. Readers should refer to the study for more information on specific details of how the figures were obtained. Table 3. Freeway Detector Annualized Per-Lane Cost Comparison
[Source: 5] One issue not addressed in the cost comparison is the level of expertise required for installation and operation. This may be a concern for some agencies. Although the non-intrusive technologies are more sophisticated, they are actually quite user-friendly. Set-up of most devices is with the use of intuitive, Windows-based software programs. Many vendors include in the price installation costs or the onsite presence of an individual during installation. There also are various end user training options available. As would be expected, each of the products listed in Table 2 has its limitations. Most manufacturers were reluctant to discuss limitations of their particular traffic data collection equipment but rather focused on general limitations of the technology. Familiarity with the limitations of each sensor type will help facilitate successful equipment selection. This information is listed in Table 4 on the following page.
Table 4. Limitations of the Technology
Comparatively assessing the performance of traffic counting devices is difficult. The differences in the technology necessitate very different installations. Selecting one particular section of highway to test all devices would seem to be optimal for comparison purposes but may not be the best assessment of a particular device’s capabilities. As has been stated previously, selection of a counting/classifying device should be based on several considerations, one of which is where the device will be installed. A site that may work well for video detection may not be optimal for passive infrared. The Texas Transportation Institute took a comparative look at the use of detectors in a freeway application in its study Evaluation of Some Existing Technologies for Vehicle Detection. The selection guide that was developed is reproduced as Table 5. TTI points out in its report that the reader should keep in mind the subjective nature of the evaluations when reviewing the data. In addition, one should remember this assessment is "only a snapshot, and it will surely change" as the technology continues to evolve. [5] Table 5. Application Guide for Detector Selection on Freeways
[Source: 5] Code: A = Excellent; B = Fair; C = Poor; D = Nonexistent; U = Unknown * A: Overhead mounting; B: Side-fire mounting
The type of traffic data collection devices available on the market has changed little in the past decade. The same thirteen technologies are still being utilized by State, county, city, and metropolitan organizations responsible for traffic monitoring operations. Some products have come and gone off the market and companies have been bought and sold, but the science remains pretty much the same. This is not to say the industry has been at a stand still. The devices have evolved as their use has come under greater scrutiny with increased usage. But, the increased usage has been more likely due to the recent focus on "intelligent transportation systems" (ITS) and the use of these devices in support of this movement. This is particularly true in the area of advanced traffic management systems (ATMS) where video image detection, Doppler microwave, passive magnetic, and passive acoustic technology are being used for signalized intersection control, incident detection and management, speed traps, and freeway metering control. As the need for collection of accurate, reliable traffic data is realized as essential for allocating scarce resources to support an aging infrastructure, greater pressure will be placed on manufacturers to make the existing technology used for traffic data collection more efficient and cost-effective.
The AZDOT Traffic Counting Survey was conducted to ascertain the current practices of State Departments of Transportation. In addition, each agency was asked their level of satisfaction with the technology in use, disadvantages identified, frequency of use and manufacturer name. The information will be used to assist in decision-making regarding changes to AZDOT’s current traffic counting practices. A two-page survey was sent to the fifty state DOTs on January 29, 2001. Prior to distribution of the survey each agency was contacted to obtain the name and address of an individual capable of providing the required information. Participants were given four weeks to respond to the survey. A list of each agency and the individual(s) completing the survey follows: Table 6. State Departments of Transportation
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