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43 the data collection electronics to a new road in a different · Does central system software provided by the vendor part of the state. allow for the conversion of formats? With this type of scenario, the highest quality (and most · What levels of data aggregation are available when col- expensive) WIM systems are not good investments. Instead, lecting data from the field (individual vehicle records, a more modestly priced sensor should be installed, with the 5-minute summaries, or hourly summaries)? intent of abandoning the site after 2 years. However, if data · How much data processing takes place at the site, and on the proposed site will be gathered for many years in order how much takes place at the central office? Can this dis- to track trends on key routes, it is often cost-effective to tribution of data processing be changed when setting up spend additional resources up front in order to reduce the cost the data collection system? of future maintenance and increase the life span of sensors · Are the data available by individual lane or for all lanes placed at a given location. at a site? A similar type of situation can also affect the selection of · What error detection and reporting mechanisms are built classification technology. If the proposed data collection site into the vendor's data collection equipment and soft- is due to be repaved in 2 years, it may not be appropriate to ware? Are error flags included in the data stream sent place sensors in the pavement. Or it may be less expensive to back from the field equipment? install non-intrusive sensors that can be used even after the pavement replacement takes place. Another area of concern for a highway agency is the staffing resources needed to install, operate, and maintain the data 4.2 DATA HANDLING AND OTHER AGENCY CONSIDERATIONS collection equipment. Staffing issues relate to the number of staff needed to place, operate, and maintain data collection The next series of basic considerations when selecting equipment, as well as the skill sets those staff need. Do the equipment pertain to how effectively new equipment can be equipment maintenance staff need specific tool sets (oscillo- integrated into the existing (or planned) data handling system scopes, video monitors, specialized circuit boards or tools, of the state highway agency. etc.) in order to maintain the equipment (i.e., diagnose and Perhaps the most important issues are what vehicle classi- repair problems)? fication categories can be collected (see Section 4.1) and how In many data collection locations, an even bigger issue is those classifications relate to the classes currently collected. the inability to gain physical access to the roadway when However, there are a number of equally important factors to desired. (Many high-volume roadways allow sensor installa- examine that relate to what other data are collected and how tion only for a limited time during the night when traffic vol- those data are handled within the highway agency's data col- umes are low and/or when other construction or maintenance lection, storage, and reporting system: activities are being performed. Can the technology selected be installed under these time constraints?) · How are the data retrieved from the data collection How long does it take to install the sensors, and what impact site? (Can the equipment be polled automatically using does that installation process have on the use of the existing telecommunications? Does a staff person need to visit roadway? Are those timeframes politically acceptable? the site? Are the data extracted directly to a computer or must they be transferred to a data storage unit and then downloaded to a computer in a second step?) · How large are the files being transferred? (How much 4.3 UNDERSTANDING EQUIPMENT communications bandwidth is needed for the site?) CHARACTERISTICS · If remote communications capabilities exist, what com- munications options are supported? (For example, what Chapter 2 presented an introduction to the technologies telephone baud rates can be used? Does the system sup- available for collecting the classification and weight data port direct Internet connections? Are digital, wireless required to meet the user needs determined from the effort modems supported? Are other communications mecha- described in Section 4.1. Additional information on equip- nisms supported that are already used by the highway ment accuracy, reliability, and cost is available through the agency?) following: · What computer formats are used as part of this data transfer, and are they proprietary to the vendor or can · References provided as part of this report, as well as the state highway agency communicate to these devices those published in a variety of technical sources; using an existing standard (e.g., the National Transporta- · Experience gained by the highway agency as it uses spe- tion Communications for ITS [intelligent transportation cific equipment; systems] Protocol, or NTCIP)? (Are these formats com- · Communication with other highway agencies about their patible with existing central database software used by experiences with specific types and models of data col- the state?) lection equipment;
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44 · Specific tests done to measure the performance of equip- It is important to obtain information about the perfor- ment; and mance of specific models offered by vendors. Similarly, it · Vendor responses to requests for proposals or requests is important to determine what warranties and/or guaranties for information published by the highway agency. vendors supply with the equipment as these provide both assurances that equipment will perform as claimed and reme- It is important to collect device-specific information from dies if the equipment does not. Lastly, it is important to test these sources. Because a specific technology appears to be the equipment when it is first placed in order to determine if a good fit for a specific application does not mean that all the equipment meets the standards warranted by the vendor. devices using that technology will work equally well. Specific Table 4.1 presents a summary sheet that can be used to high- implementations of a given technology from two different light the specific data collection issues important to selecting vendors can result in data of very different quality. Similarly, the appropriate equipment for a specific project or set of data the cost for specific technologies can vary considerably from collection efforts. (Additional factors can also be added to vendor to vendor, along with the features supplied with the reflect needs not discussed in this document.) It is up to each proposed equipment. Only by looking at the specifics of ven- highway agency to weigh the relative importance of each of dors' proposals can these details be determined and compared. these issues.
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45 TABLE 4.1 Sample equipment selection analysis summary sheet Technology/Vendor/Model: Technology/Vendor Subject Area Issues/Concerns Review Comments Equipment Capability Type of Data Collected · WIM · Classification Types of Vehicle Classes Measured · 13 FHWA axle-based classes · Vehicle lengths only · Other (total number allowed) Desired/Required Sensor Location Can sensor be placed? · In pavement · Condition of pavement, planned pavement · On pavement maintenance and repair? · Non-intrusive · Traffic volumes · Availability of overhead structures or poles Count Duration · Seasonal changes? (in traffic generators?) · Portable (several days) · Correlation with permanent sites, reliability · Permanent of measurements? Output from Device · Can be polled from central source, or only · Level of aggregation from the site? · Specific · Flexibility of output formats · Quality-control metrics available for · Availability of standardized formats analysis of device output (NTCIP? Other?) Site Conditions Operating Environment · Temperature range and daily variation · Visibility constraints (fog, mist, dust) · Snow (loss of lane lines) · Free-flow or congested traffic (including other acceleration/ deceleration conditions) Number of Lanes · Number of sensors required · Are all lanes next to a shoulder? · Number of sets of electronics required Is Power Available? Can device run off of solar panels? Are Communications Available? Bandwidth required from device · Telephone, DSL, wireless · Frequency of communications · Other General Technology Price Total Cost = Sensor Cost x Number of Sensors + Cost of Electronics Staff Training to Install, Operate, and Maintain the Devices Equipment Needed to Install, Operate, and Maintain the Device Published Accuracy Achieved with the Has the technology been used previously? Technology Previous Experience with this Vendor support offered/available Technology/Vendor