ITS Solutions CVO / Truck Enforcement FAQs
FAQs
What WIM technology should I choose for enforcement screening?
Two things are important when using WIM for enforcement screening: the accuracy of the WIM scale and the cost of the WIM technology over its lifetime. The Single Load Cell (SLC) Scale is by far the most popular scale used to provide weight enforcement screening for mainline and ramp applications for exactly these reasons. Eighty to ninety percent of the mainline weight screening systems in the United States have incorporated this scale. The SLC Scale meets and exceeds the highest ASTM E1318-02 accuracy requirements, i.e. Type III or 6 % error on Gross Vehicle Weight (GVW). The high accuracy of the scale translates into a very low chance of incorrectly sorting a truck (five percent or less), compared to other technologies such as bending plate and piezoelectric that have a corresponding figure of approximately twenty-five and forty percent. This is significant at very busy sites where maximum efficiency is required. At lower volume sites, a less efficient technology may be acceptable. The scale is easily maintained, as the one load cell can be replaced in thirty minutes with hand tools without removing the scale from the roadway. The SLC scale also has a long life, with some scales operating for 20 years or more. Due to the long life and low maintenance, the SLC scale is superior to other types of WIM in-road scales and sensors.
There are over 8 million trucks in the United States, yet only approximately 700,000 are enrolled in the Norpass and Prepass preclearance programs. How can I increase the number of trucks I can screen on the mainline given the current low transponder distribution level?
Weight screening can be performed on the main highway. Trucks can be signaled to either bypass the weigh station or report to the weigh station using fiber optic changeable message signs (cms) that incorporate a narrow cone of vision, so the intended truck and only the intended truck sees the message on the sign. Cameras positioned at the WIM in both lanes of travel, and at the entrance to the station, enhance the sorting by allowing the operators to see freeze frame images of trucks reporting, trucks wrongly in the left lane of travel, or those incorrectly bypassing the weigh station. This approach lets you at least perform a size and weight check on all the traffic without the situation arising that requires the station to be closed as a result of the traffic causing a backup in the station.
How do IRD Systems fit into the CVISN initiative?
IRD provides an Integrated Roadside Operating Computer (I-ROC) that collects the AVI and WIM data on a truck, queries the state CVIEW program, and returns a report or bypass to the truck through its in-cab transponder. If the state has not yet established their CVIEW system (the State operated database for commercial vehicle credentials), commercial and public domain versions exist, including Washington State's XVIEW, a public domain database that States can develop. The IRD I-ROC system can integrate with any CVIEW system implemented in a State. IRD can also provide a CVISN check on trucks without transponders at the weigh station by having the station operator enter trucks' license plates into the system.
Why should I choose Mainline over Ramp Sorting?
The major reason is cost. Existing weigh stations do not normally easily incorporate ramp sorting without land purchase and significant additional construction costs. Two factors are responsible for extensive construction with respect to ramp sorter stations: 1) the distance required to line up trucks at the static scale and 2) the distance required from the highway exit to the Weigh-In-Motion scales so the trucks are no longer significantly decelerating when crossing the scales. Both of these distances can be 1000 feet or more and most existing station layouts cannot accommodate these distances.
There are also safety and environmental reasons for choosing a mainline sorter. Every truck that exits and re-enters the freeway results in potential traffic conflicts and extra fuel usage and emissions as the vehicle must slow and then return to freeway speed.
The other major reason for selecting Mainline Sorting over Ramp Sorting is that the Federal CVISN, Norpass and Prepass preclearance programs are all designed for and promote mainline screening.
How can a Single Load Cell Scale weigh a truck wheel the same on the outside of the platform as on the center of the platform when there is only one load cell in the scale weigh pad?
Torsion bars around the outside of the scale platform transfer the load so that the center load cell experiences the same weight no matter where the truck wheel is on the platform, as long as the wheel is fully on the platform. Offscale detectors detect if a wheel is not fully on the scale. If a wheel is detected as not fully on the scale, then the truck is directed to report to the static scale.
How often do you need to calibrate the Single Load Cell scale? Is there an auto calibration feature that involves the static scale?
The IRD Single Load Cell WIM Scale operates in a stable and consistent manner regardless of the environmental conditions, or temperatures. Properly installed, the IRD Single Load Cell WIM Scale does not require continuous calibration as required by some other WIM technologies. IRD WIM systems have an integrated auto-calibration software routine that can automatically and continuously compare the performance of the WIM system to the static weights of the trucks. The system is flexible in that auto-calibration can be automatic if a variation is seen, or can alert the operator that a potential problem with the system has been detected as a result of the difference.
Is it necessary to have a 300' concrete slab in the vicinity of the WIM scale?
The accuracy of the WIM scale is dependent upon the smoothness of the road as specified in ASTM E1318-02. A concrete slab is a good idea at ramp sorters where trucks brake as they leave the highway. However, several states have successfully implemented and operate mainline sorter scales installed in asphalt that is and well maintained.
