How in-motion, pre-scan weigh station technology could affect specialized and heavy equipment haulers

Updated Sep 2, 2015

Abrams Weigh ScaleWe all are aware of the “red light cameras” that have been around for some time. The technology works through a sensor embedded in the roadway with companion systems tracking the status of the light. A camera or cameras are positioned to take a picture(s) of the vehicle, license plate, and driver. This photographic evidence is obtained if the sensor detects a vehicle in the intersection while the condition of the light is red. If both are “true,” a ticket is mailed to the registered owner.

Arguments about “fairness” may continue and no one is happy when one of these citations arrives, but what most can agree on is that enforcement officers have higher priorities than trying to catch motorists and truckers “pushing the yellow” or “blowing the red.” Other automatic systems in use to issue speeding tickets are much more common in Europe than they are in North America, but work much the same way—with much the same results.

Vehicle inspectors, weigh scale operations, enforcement officers, and states would like to see the same “targeted enforcement” for vehicle size and weight. The technology is available, but again, is much more widely used in Europe than North America. It’s difficult to argue against this technology; it keeps safe-operating heavy haulers moving while cracking down on the minority that cause problems for the majority.

Selective and targeted enforcement is not new in the United States; programs that allow safe carriers to bypass scales have been around for some time. However, most programs historically have not taken into account the vehicle’s actual movement approaching the scale. What is the gross vehicle weight, what are the bridge distances and weights, what are the dimensions—length, width, and height?

Identifying the vehicle and carrier, and seeing the actual weights and measurements (or at least pre-scale indications) are the most effective tools for complete targeted enforcement.

There have been rumors this summer that states were going to start sharing scale information even if a scale house was closed. The rumors appear to be without basis. Some of the states mentioned in the rumors were not connected and in fact are far enough apart that most traffic would never throughput. This doesn’t mean that local enforcement is not, or cannot be, alerted when technology indicates that there is an overdimension or overweight load in the area.

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What technology do the states use?

The technology to pre-scan for size and weight has been around for some time, but to implement effective solutions is expensive. From a high level, the technology involves weigh-in-motion (WIM) or Virtual Weigh Stations (VWS).

The Federal Highway Administration (FHWA) describes WIM systems as:

  • A scale or set of sensors on the mainline or installed on a ramp that records the impact of the passing vehicle;
  • A roadside cabinet containing a processor that converts the downward force readings of the vehicle on the scale into data estimating the vehicle’s gross weight and axle weights; and
  • A communication system that transmits the weight data to the computers of enforcement personnel or to an enterprise-level WIM database management system. Typically, dial-up communication is used to transmit data from WIM systems to users, but in order to support enforcement functions, high-speed wireless or digital subscriber line (DSL) technology is necessary to transmit real-time data and/or vehicle images.

The accuracy of the gross vehicle weight or axle weight estimate as computed by the roadside processor can be affected by the WIM scale technology in use. When installed on the mainline, more expensive WIM systems have less variance in their readings and may better compensate for filtering external factors that affect vehicle weight calculations. Conversely, less expensive WIM scales or sensors may not be as accurate at highway speed.

Virtual Weigh Stations (VWS) step up the technology requirements. As described by the FHWA, “The hardware requirements of a virtual weigh station are similar to that of a mobile screening site, but a virtual weigh station includes the addition of a digital imaging system, at minimum, and possibly additional technologies. Other technologies present at the site may eliminate the need for digital imaging. A virtual site has no permanent (continuous) on-site staff, therefore, WIM used for mobile screening is a simple version of a virtual weigh station site.”

“A virtual weigh station is a roadside enforcement facility that does not require continuous staffing and is monitored from another location. Typical hardware deployed at a virtual weigh station includes a WIM installation, a camera system, and high-speed communications for use in real-time truck screening operations. Virtual weigh stations are intended to mimic the capabilities of a fixed weigh station.”

It is important to know that currently, unlike “red light cameras,” WIM and VWS technologies are not used for direct enforcement in North America. WIMs are used to keep trucks moving that do not have apparent conditions of being over dimensional or overweight nor have an “inspect” recommendation from other Inspection Selection Systems (ISS). Direct enforcement could come—currently the European nation of the Czech Republic uses a sophisticated system directly.

Understanding that these programs are in place and growing, it is more imperative than ever for heavy and specialized carriers to ensure that the “’i’s are dotted and the t’s are crossed” on any special permits and that drivers are not exceeding the allowances or bridge dimensions and axle weights.