The National Academies Press

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From page 1... ... data collection equipment collects both truck volume and load spectra, but the equipment is more expensive to obtain and more difficult to install and operate than equipment that can only count and classify vehicles. Therefore, highway agencies routinely use a combination of WIM and simpler vehicle classification equipment to collect the data they require for pavement design. Read the entire page →
From page 2... ... Understanding those strengths and weaknesses allows a highway agency to select equipment that is more likely to work in a specific situation. While different vendors are often capable of designing around a given technology's weaknesses, the odds of obtaining accurate data are certainly increased by taking advantage of specific technology strengths and avoiding known technology weaknesses. Read the entire page →
From page 3... ... S.2.1 Intrusive or Non-Intrusive Sensors Perhaps the first question that should be asked when deciding between intrusive and non-intrusive equipment is "Can the portable equipment be safely installed in the roadway section in question? " In most cases, intrusive sensors provide more descriptive vehicle classification data than non-intrusive sensors, especially where the sensors provide axle count and spacing information. Read the entire page →
From page 4... ... TABLE S.1 Short-duration classification technology comparisons Read the entire page →
From page 5... ... Ideally, the classification procedure used by a portable counter should match that used by WIM devices in the state. The highway agency can accomplish this by supplying the vendor of a selected device with the classification algorithm used to convert axle count and spacing information into an estimate of vehicle classification. Read the entire page →
From page 6... ... S.3 PERMANENT VEHICLE CLASSIFICATION EQUIPMENT For purposes of this report, "permanent" equipment is differentiated from "shortduration" equipment both because permanent equipment requires more resources to initially place and because its counting session can (but does not necessarily have to) last longer. Read the entire page →
From page 7... ... TABLE S.2 Permanent classification technology comparisons (continued on next page) Read the entire page →
From page 8... ... TABLE S.2 (Continued) Read the entire page →
From page 9... ... This is partly because poor pavement conditions increase vehicle dynamics, which in turn increase the impact loads applied to intrusive sensors. But poor pavement condition also commonly leads to premature failure of the pavement/sensor bond, and the Read the entire page →
From page 10... ... Consequently, pavement life should be considered when the life expectancy of a permanent site is computed, and the cost/performance decision should be adjusted accordingly. S.3.3 Vehicle Classes Collected As with short-duration counts, the preferred vehicle classification scheme for permanent classifiers is axle based, which means that, all things being equal, intrusive, axle sensor-based classifiers are the preferred technology for meeting the pavement design guide requirements for traffic load data. Read the entire page →
From page 11... ... Where the pavement cannot support accurate WIM data collection, the highway agency should consider moving the data collection site to a location at which the WIM can function accurately. Finally, as with permanent vehicle classifiers, the highway agency should consider expected pavement life when determining the life expectancy of a WIM site, as well as the implications of that life span for the WIM technology for that site. Read the entire page →
From page 12... ... TABLE S.3 Weigh-in-motion technology comparisons Read the entire page →
From page 13... ... When these calibration costs are accounted for, many highway agencies find that portable WIM becomes cost prohibitive relative to the use of "short-term permanent" WIM (placing WIM sensors permanently in the ground, but only collecting data from the sensors periodically for moderately short periods) Read the entire page →
From page 14... ... that decrease the smoothness of the transition from the pavement surface to the WIM sensor surface cause impact loads and increased vehicle dynamics, both of which contribute to loss of WIM system accuracy. S.5 ADDITIONAL GENERAL GUIDANCE While it is important to select technologies that can operate in the conditions in which they are installed, a successful data collection program will also incorporate all of the attributes presented below. Read the entire page →
From page 15... ... 15 • Make sure that the staff installing the equipment are fully trained in the installation of that equipment and that they understand the factors that affect its performance. • Maintain a preventive and corrective maintenance program to ensure that data collection equipment reaches its expected life and that the data provided are accurate. Read the entire page →

From page 1...

... data collection equipment collects both truck volume and load spectra, but the equipment is more expensive to obtain and more difficult to install and operate than equipment that can only count and classify vehicles. Therefore, highway agencies routinely use a combination of WIM and simpler vehicle classification equipment to collect the data they require for pavement design.

Summary Pages 1-15

Summary
Pages 1-15