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47 than makes up for any "extra" counts that are taken but not neers and traffic data collectors and (2) combining that com- actually used because expected pavement projects are delayed. munication with strong advance planning. Both pavement Data collection staff have the responsibility of coordinat- design engineers and traffic data collectors obtain consider- ing the needs of different users. A key to this function is able benefits from improving communications. Well-run traf- knowing where flexibility exists in the collection and report- fic counting programs invariably have strong connections to ing of data. In a simple example, if two users request the same their users, and the pavement design section is a very impor- data for the same road but for road segments one-half mile tant user group. apart, the data collection staff need to be able to determine if those two data collection requests can be met by a single 5.2 DETERMINE SITE LOCATION count, halving the number of counts that need to be taken. AND SYSTEM REQUIREMENTS Where flexibility exists is a function of the roadway char- acteristics and the uses of the data. If the road is a rural high- As noted in the example in the previous section, a key way with limited activity, the two requests can likely be met component of the data collection process is understanding with one count. If a major freeway interchange occurs between what, where, and why data are being collected. Understand- the two locations, it is unlikely that the two counts can be ing these factors is necessary for determining exactly what, combined. Still, the same data collection crew will probably when, and how data need to be collected and for selecting the collect both counts, and by collecting both counts in the same equipment to be used. trip at least the travel time and cost associated with the data Traffic data are collected from a given location either collection can be halved. because data from that point are important to a specific design Traditionally, this type of coordination has been difficult to or project, or because data from that location are needed to perform because pavement project selection processes were help develop a default or average value that can be used at not done early enough to fit into traffic data collection sched- many sites where site-specific information cannot be afford- ules. However, most states now operate pavement manage- ably collected. The first of these count efforts is generally ment systems that identify roadway sections in need of repair referred to as "project counts." These generally are data col- or rehabilitation in the near future. These program outputs can lected (1) to describe the current traffic stream crossing the be used to create a short list of projects that are likely to occur design lane for a project and (2) to serve as a baseline upon in the next 2 years. The state's transportation improvement which to forecast the future traffic stream. The second data plan (TIP) may also provide such a list. If the actual pavement collection effort is often thought of as planning counts, which design list is not available when the traffic data collection pro- are performed as part of general agency data collection efforts. gram needs to be developed, this slightly larger list can be used While also meeting general agency needs, these data are as a surrogate for the actual list. It may require a minor increase used to compute the Level 2 and Level 3 load-spectra in the number of pavement design counts that need to be col- defaults1 used by the pavement design software. These counts lected, but the slight increase in counts is more than offset by include WIM efforts used to compute truck weight road group the decrease in cost per count due not only to the coordination (TWRG2) axle-load distributions, and continuous classifica- tion counts are used to determine seasonal truck volume and efforts, but also to the more timely manner in which data can other truck traffic patterns. Some flexibility exists in the col- be made available to the pavement design team. lection of both of these types of data. Implementation of the recommendation to enhance the Ideally, project-specific counts are taken at the project site, communication and coordination of pavement design engi- as this provides the most reliable estimate of current traffic neers and traffic data collectors is more of an administrative crossing the design pavement. However, the actual data col- and institutional problem than a technical problem. If an lection effort can be moved upstream or downstream from agency succeeds, four positive changes should take place: the project location if the project location is not conducive to accurate traffic data collection or if other circumstances war- · The availability of traffic load data for pavement design rant such a move. One good reason to move a project-specific purposes should improve. count is that the pavement at the project site is in such poor · The cost of collecting traffic load data for pavement condition that the available traffic sensors will not work accu- design should decline. rately. In general, having accurate, representative data is more · Data quality should improve as more staff review and important than having data from the exact site of the pave- use the data collected. ment project. · Internal support for traffic data collection activities should improve as the users of the data improve their 1 Level 2 load-spectra defaults are those axle weight distributions used when site- understanding of the value and limitations of the traffic specific data for a project site are not available, but when the site can be identified with a regional average. (Level 2 is the regional average.) Level 3 represents the statewide data they are receiving. average and is used only when no better information is available for a pavement design. 2 TWRGs are groups of roads that have trucks with similar loading conditions. A sample of vehicle weights is collected and used to represent the axle load distribution The keys to all of these improvements are (1) achieving a for all roads that belong to that group when site-specific load information is not high level of communication between pavement design engi- available.