Office of Operations Freight Management and Operations

2.0 Current Situation

2.1 Background

Unstaffed and remotely monitored roadside enforcement facilities – commonly called virtual weigh stations – are deployed to address some of the deficiencies in states’ traditional roadside enforcement programs.  These facilities can expand the geographic scope and effectiveness of a State’s truck size and weight enforcement program by monitoring and screening commercial vehicles on routes that bypass fixed inspection stations and on secondary roadways, as well as in heavily populated urban or geographically remote locations where it may be difficult to deploy traditional enforcement operations.  Data from virtual weigh station sites also can effectively target enforcement resources on roadways where overweight trucks are known or are suspected to operate.

2.2 Overview of Fixed Roadside Enforcement Operations

Fixed weigh or inspection stations are the backbone of most states’ truck size and weight enforcement programs.  In many states, the majority of weight inspections are conducted at weigh stations.  These facilities intercept commercial vehicles entering or passing through a State on major highways.  Currently, approximately 680 weigh stations are in operation in the United States. (2009 Rand McNally Motor Carriers’ Road Atlas, 2009.  Massachusetts and New York are the only states that indicate there are no permanent weigh stations used in the State.) Customarily, signs on the highway direct commercial vehicles to pull into the stations where they are weighed by static scales to ensure that they are within Federal and State regulations.  Both total gross weight and individual axle weights are measured and displayed to station operators.  The primary purpose of these stations is to enforce truck weight regulations, in order to protect the infrastructure from excessive wear and tear caused by overweight trucks.  

It is efficient to screen trucks for safety, credentials, and logbook violations at the same time they are weighed.  At the static scale, the truck is checked for obvious safety problems and for proper credentials, including the driver’s medical examination certificate and commercial driver license.  In case of a problem, the truck is directed to an inspection area within the station for a closer examination.  Some trucks may be selected for closer inspection in a random manner or because of the officer’s experience with the carrier, in addition to visual clues seen by the officer.  In many cases, officers will use identifying information on the truck to query safety and credentialing data repositories (e.g., State Commercial Vehicle Information Exchange Window [CVIEW], national Safety and Fitness Electronic Records [SAFER]) to determine if the carrier has a history of poor safety performance and/or to verify the current status of motor carrier and commercial vehicle credentials.  For example, the USDOT or license plate number can be used in a manual or automated check of a carrier or vehicle database (e.g., CVIEW), yielding an Inspection Selection System (ISS) inspection value and recommendation or registration or tax payment status.  The ISS is a decision-aid for commercial vehicle/driver inspections, which guides inspectors in selecting vehicles for inspection; the ISS value or score is based on a motor carrier’s safety performance data.

The effectiveness of fixed weigh stations is affected by:

  • Limited physical and processing capacity that can be regularly overwhelmed, resulting in commercial vehicles backing up onto the highway and requiring closure of the station so that public safety is not impacted by the lengthening queue;
  • Limited geographic coverage (i.e., each facility supports enforcement monitoring over a limited portion of a roadway);
  • Limited hours of operation, which largely are driven by availability of staffing and financial resources;
  • Inability to deploy fixed sites in some areas (e.g., remote, urban) that are in need of commercial vehicle enforcement; and
  • Expenses associated with the acquisition, development, operation, and maintenance of the sites.

These stations also can cause motor carrier delays that range from a few minutes to extended queue times for trucks waiting to be weighed.  Unnecessary delays and prolonged transit times adversely impact a carrier’s ability to bid competitively on delivery contracts.

In order to address some of these limitations, the vast majority of states currently support electronic screening at many of their fixed facilities.  Electronic screening is the automated screening of vehicles that pass a roadside check station, determining whether further inspection or verification of credentials is required, and taking appropriate actions.  Electronic screening requires a change in the traditional concept of pulling in every truck for weighing and inspection.  In electronic screening, commercial vehicle traffic is sorted to distinguish between known or likely safe and legal vehicles and potential violators before they stop at an inspection facility.  The intent of electronic screening is to allow safe and legal trucks to pass the station while enforcement resources are focused on high-risk carriers and vehicles.  Mainline weigh-in-motion (WIM) is frequently used as part of an electronic screening system, providing real-time weight verification concurrent with automated safety and credentials verification for bypass eligibility.  Vehicles cleared for bypass are not generally directed to pull into the weigh station.

States with electronic screening have reported a reduction of 15 to 20 percent in the volume of truck traffic passing through weigh stations that are instrumented with the capability.  The reduction is directly related to the level of participation in electronic screening by motor carriers.  Clearly, the greater the participation of carriers in electronic screening programs, the less likely it is for queuing to close weigh stations and legal trucks to need to pull into weigh stations.  The benefit to the carrier is the ability to travel past the weigh station without stopping.  For the State, electronic screening allows enforcement resources to be focused on high-risk carriers and vehicles.

Electronic screening cannot address all of the limitations associated with fixed weigh stations.  Even with electronic screening, noncompliant vehicles can attempt to bypass the enforcement station by using a route that goes around the site.  Weigh stations also may have restricted and often predictable hours of operations.  As a result, overweight trucks may travel when weigh stations are closed, at night, and on weekends.  Electronic screening also does not address the costs and the physical space that are required to deploy a weigh station.

Because weigh stations often are bypassed or otherwise avoided by overweight trucks, significant effort is expended on compliant carriers, providing incentive for states to implement tools and methods to better target high-risk carriers and vehicles.

2.3 Overview of Mobile Roadside Enforcement Operations

Mobile enforcement consists of enforcement activities that do not take place at fixed weigh or inspection stations.  States’ mobile enforcement programs usually encompass temporary roadside locations (e.g., rest areas, modified shoulders, abandoned weigh stations), roving patrols, or both.  These activities typically are conducted on routes without fixed weigh stations, on secondary roadways, and in remote areas.  Mobile enforcement allows states to expand their enforcement efforts away from the Interstate and major highways and onto secondary and smaller roads that are known bypass routes around fixed stations.

During mobile enforcement details, commercial vehicles are stopped and weighed on portable scales.  States also may opt to conduct a safety inspection, and/or credentials verification based on random selection, visual clues, or experience (or inexperience) with a particular carrier.  At the roadside, common visual clues are an appearance of being overweight and observed safety problems. Enforcement officers may stop a vehicle after an automated (using a laptop computer capable of accessing a database or the Internet) or radio check of the driver’s license number, vehicle license plate number and/or vehicle identification number (VIN), or USDOT number.  If a temporary roadside location is being used, officers may attempt to stop all approaching trucks, depending on traffic conditions. Note that in some states, probable cause is required to stop a vehicle. 

Compared to weigh stations, mobile weight enforcement operations process a smaller volume of trucks, although the percentage of violators is arguably higher.  Similarly, most safety inspections are conducted at weigh stations (where it is a safe place to put a truck out-of-service), but indications are that the number of inspections is growing at mobile locations.

Incorporating WIM systems into mobile operations provides the State with the potential to weigh a greater number of trucks.  WIM equipment can be installed in the pavement or it can be portable.  Mobile teams can set up in vans and move equipment around as needed, or they can set up in the area of a permanently installed WIM system.  Real-time WIM data can be viewed by roadside enforcement personnel on laptop computers, who visually identify the potential violators.  Automatic identification of violators (relieving the need for manual visual recognition of suspect vehicles) is possible with the incorporation of advanced roadside-based technologies (e.g., license plate readers).

The importance of mobile operations in states’ overall commercial vehicle enforcement programs is increasing as many states “deemphasize” weigh stations that are expensive to build and maintain.  However, the effectiveness of mobile units is limited by the number of roadside personnel that can be deployed by a State.  Furthermore, with dwindling resources, it is difficult for states to expand mobile enforcement coverage.  Under such conditions, just as weigh stations equipped with electronic screening attempt to focus on high-risk operators, states are pursuing new ways to effectively target their resources on high-risk carriers, drivers, and vehicles during mobile operations.

2.4 Overview of Existing Virtual Weigh Station Deployments

At least 10 states across the United States have deployed a virtual weigh station to date.  States deploy virtual weigh stations in order to enforce legal truck weights and to protect the State’s investment in the infrastructure.   These states’ deployments vary in terms of their operational focus (e.g., screening commercial vehicles, supporting planning for the deployment of enforcement resources) and technologies used (e.g., WIM, license plate reader, USDOT number reader).  These deployments are documented in a FHWA study of the state of the practice regarding virtual weigh station deployments. (State of the Practice of Roadside Technologies, submitted by Cambridge Systematics to the Federal Highway Administration, May 2009, as part of the Truck Size and Weight Enforcement Technology Project.) What all of these deployments have in common is a WIM system that supports real-time screening activities at locations that are unstaffed and away from weigh stations. 

In Fiscal Years 2006 – 2008 a total of 14 jurisdictions received Federal CVISN Deployment Grants for virtual weigh station deployments (a few of these states have completed their deployments and are counted in the 10 states mentioned above).  These states’ virtual weigh station deployments may include – in addition to WIM scales or sensors – cameras, optical character recognition (OCR) technology, system electronics, screening software, system integration, and/or expanded communication networks to support the timely and secure transmission of data to users, as well as integration of safety data/screening algorithms into roadside operations.

Some states have deployed VWS technology as part of a mobile screening system in which an officer at the roadside with a laptop computer receives individual axle weights and gross vehicle weights that are wirelessly transmitted from the WIM device on the mainline that is being monitored to the mobile officer’s laptop.  The officer physically monitors the real-time WIM data on the laptop and visually identifies the trucks that are overweight according to the data received.  The potentially overweight trucks are then intercepted for inspection after traveling past the WIM site.  Having quantifiable performance measurements avoids stopping vehicles that are legal according to weight thresholds established by the State.

A few states have added a roadside digital camera system to the mobile screening system to facilitate the identification of suspect commercial vehicles.  In these operations, an enforcement officer views the real-time WIM data linked with a vehicle photo on a laptop computer in the patrol vehicle located downstream of the WIM site.  Multiple photos also may be displayed in thumbnail form so the officer can easily select from different views of the vehicle of interest.  Suspect vehicles are identified on the laptop, facilitated by visual and/or sound alerts.  In one scenario, the officer monitors the data and images and intercepts the violators.  The same data and images may be viewed by enforcement personnel in a fixed facility.  In a different scenario that is deployed by states, instead of an officer located downstream performing monitoring and weighing functions, personnel viewing the WIM data and images at a nearby weigh station will dispatch nearby enforcement units to intercept and weigh suspect vehicles identified on the monitor. 

As part of the “2006 Commercial Motor Vehicle Size and Weight Enforcement in Europe” scan sponsored by FHWA in cooperation with the American Association of State Highway and Transportation Officials (AASHTO) and the National Cooperative Highway Research Program (NCHRP), the scan team observed the use of high-speed weigh-in-motion (HSWIM) and vehicle image capture using digital cameras as a common enforcement site layout.  The COST (Cooperation in Science and Technology) 323 truck weight enforcement protocol used throughout Europe since the late 1990s, entitled WIM/VID, calls for WIM/visual identification capability for screening at the roadside.  The simultaneously captured picture of the motor vehicle and its associated axle and gross vehicle weight values are used immediately by enforcement officials who are preselecting certain trucks for more extensive inspections, or the data are processed and stored for further analysis and use at a later time.

This system configuration (i.e., “bundled” WIM and digital imaging functions) is not currently deployed in the United States; however, it is now readily available in North America.  “Off-the-shelf” virtual weigh station technology packages including digital image capture coupled with HSWIM telemetry are offered by several vendors at this time. 

Several states have deployed a license plate reader (LPR) or USDOT number reader to provide automatic vehicle identification (AVI).  These technologies use a digital camera or cameras augmented with specialized OCR software to isolate and identify specific characters and numbers making up a license plate number and/or USDOT number.  AVI relieves the need for any kind of manual visual recognition, whether it is based on direct observation of the vehicle itself or examining a photo of the vehicle. 

The concepts of operations for basic and expanded virtual weigh stations are provided in Section 4.0.

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