Prototype Weigh-In-Motion Performance
- ORNL
Oak Ridge National Laboratory (ORNL) has developed and patented methods to weigh slowly moving vehicles. We have used this technology to produce a portable weigh-in-motion system that is robust and accurate. This report documents the performance of the second-generation portable weigh-in-motion prototype (WIM Gen II). The results of three modes of weight determination are compared in this report: WIM Gen II dynamic mode, WIM Gen II stop-and-go mode, and static (parked) mode on in-ground, static scales. The WIM dynamic mode measures axle weights as the vehicle passes over the system at speeds of 3 to 7 miles per hour (1.3 to 3.1 meters/second). The WIM stop-and-go mode measures the weight of each axle of the vehicle as the axles are successively positioned on a side-by-side pair of WIM measurement pads. In both measurement modes the center of balance (CB) and the total weight are obtained by a straight-forward calculation from axle weights and axle spacings. The performance metric is measurement error (in percent), which is defined as 100 x (sample standard deviation)/(average); see Appendix A for details. We have insufficient data to show that this metric is predictive. This report details the results of weight measurements performed in May 2005 at two sites using different types of vehicles at each site. In addition to the weight measurements, the testing enabled refinements to the test methodology and facilitated an assessment of the influence of vehicle speed on the dynamic-mode measurements. The initial test at the National Transportation Research Center in Knoxville, TN, involved measurements of passenger and light-duty commercial vehicles. A subsequent test at the Arrival/Departure Airfield Control Group (A/DACG) facility in Ft. Bragg, NC, involved military vehicles with gross weights between 3,000 and 75,000 pounds (1,356 to 33,900 kilograms) with a 20,000-pound (9,040 kilograms) limit per axle. For each vehicle, four or more separate measurements were done using each weighing mode. WIM dynamic, WIM stop-and-go, and static-mode scale measurements were compared for total vehicle weight and the weight of the individual axles. We made WIM dynamic mode measurements with three assemblages of weight-transducer pads to assess the performance with varying numbers (2, 4, and 6) of weigh pads. Percent error in the WIM dynamic mode was 0.51%, 0.37%, and 0.37% for total vehicle weight and 0.77%, 0.50%, and 0.47% for single-axle weight for the two-, four-, and six-pad systems, respectively. Errors in the WIM stop-and-go mode were 0.55% for total vehicle weight and 0.62% for single-axle weights. In-ground scales weighed these vehicles with an error of 0.04% (within Army specifications) for total vehicle weight, and an error of 0.86% for single-axle weight. These results show that (1) the WIM error in single-axle weight was less than that obtained from in-ground static scales; (2) the WIM system eliminates time-consuming manual procedures, human errors, and safety concerns; and (3) measurement error for the WIM prototype was less than 1% (within Army requirements for this project). All the tests were performed on smooth, dry, level, concrete surfaces. Tests under non-ideal surface conditions are needed (e.g., rough but level, sun-baked asphalt, wet pavement), and future work will test WIM performance under these conditions. However, we expect the performance will be as good as, if not better than, the present WIM performance. We recommend the WIM stop-and-go mode under non-ideal surface conditions. We anticipate no performance degradation, assuming no subsurface deformation occurs.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). National Transportation Research Center (NTRC)
- Sponsoring Organization:
- Work for Others (WFO)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 931526
- Report Number(s):
- ORNL/TM-2007/039; 400403209; ORNL/TM-2005-164; TRN: US200813%%304
- Country of Publication:
- United States
- Language:
- English
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