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46 CHAPTER 5 BEST PRACTICES FOR EQUIPMENT USE The collection of traffic load data required by the pave- 5.1 IDENTIFY USER REQUIREMENTS ment design software is just one of a variety of traffic data collection tasks that highway agencies must perform. The The pavement design process requires an accurate estimate traffic load data collection effort cannot be done as an inde- of the number of heavy vehicles projected to use the roadway pendent activity. It must be performed within the context of lane being designed and the number, type, and weight distri- the entire traffic data collection effort undertaken by a high- bution of the axles on those trucks. These data will come way agency. from a combination of project-specific counts and the sum- Determination of what equipment to purchase and how to mary tables developed from the general truck counting and install, calibrate, and maintain it, as well as what data to col- weighing program performed by the state highway agency. lect, how equipment and staffing resources are efficiently The level of reliability desired by pavement design engi- used to collect it, and how the collected data are manipulated, neers (and the budget available to them for data collection) stored, and reported once they are available, must be done will result in their selection of the level of data collection per- formed for pavement design projects. The level will define within the context of the entire agency's traffic data needs. the amount of truck volume and weight data collected specif- Separation of the pavement design needs from the other traf- ically to meet the needs of pavement design efforts. These fic data needs leads to considerable inefficiency in traffic data needs will become requests to collect specific data that are collection. Therefore, a need for good data practices applies sent to the traffic data collection section of an agency. throughout the agency's traffic data collection program. Traffic data collection units will need to develop mecha- In general, good data collection practice can be summa- nisms that allow them to efficiently respond to both these spe- rized as nine basic steps: cific requests (which will vary from request to request) and the need to collect the more general data that are used to create the 1. Identify user requirements and develop an implemen- summary statistics and tables used when project-specific data tation plan. are not required or cannot be affordably collected. 2. Determine location and system requirements. To create a cost-effective data collection program, both 3. Determine site design life and accuracy necessary to of the above needs must be efficiently coordinated with the support the end user. other truck volume and weight data needs of the highway 4. Budget the resources necessary to support the selected agency. Collecting the data needed for general summary site design life and accuracy requirements. tables is part of routine data collection programs, and direc- 5. Develop and maintain a thorough quality assurance and tions for this are included in the FHWA's Traffic Monitor- performance measurement program. ing Guide, Sections 4 and 5. Responding efficiently to the 6. Purchase the WIM or classification equipment with a need for project-specific counts is a more difficult under- warranty. taking. Often it can most effectively be accomplished by set- 7. Manage the equipment installation. ting up one or more meetings during each year between traf- 8. Calibrate and maintain calibration of equipment. fic data collection staff and pavement design staff to discuss 9. Conduct preventive and corrective maintenance at the roadway sections that will most likely be the subject of new data collection sites. pavement designs in the next year or two. These sections will require truck traffic data collection, and a 1- to 2-year time- frame should allow efficient scheduling of the data collec- It is important to remember that good traffic data collec- tion effort. tion practice requires the agency to also consider the impact Scheduling this meeting (or meetings) to take place prior to on data collection of other traffic data needs. This section the development of each year's traffic data collection program expands on the traffic data collection and equipment needs allows data collection staff to efficiently schedule their data discussed elsewhere in the report by explaining how pave- collection resources. This significantly decreases the cost of ment design data needs fit together with other agency needs. data collection efforts, and this scheduling efficiency more