Office of Operations Freight Management and Operations

4.0 Statistics Collection and Planning

Mainline WIM systems are commonly used to collect traffic characteristics information for analysis of travel and weight trends, pavement and bridge monitoring and management, pavement design, and development of emissions models.  WIM systems used for traffic monitoring may serve “double duty” for preselection as well as statistics collection and planning.  Some states use the WIM information to assign enforcement resources. 

The hardware requirements for the collection of WIM data for planning purposes are similar to those described in the “WIM Technology Overview” section above.  Typically, the primary customer of the data is the State’s Department of Transportation (DOT) or Department of Highways.  The data is processed and displayed to satisfy customer needs.  States may implement specialized tools and applications to provide useful information from WIM data.  Data is collected continuously, which maximizes a State’s ability to conduct pavement monitoring and research and make pavement design decisions.  Oregon has published a report describing the use of WIM in load spectra analysis.  Of the states that were interviewed, contacts from North Dakota voiced their intent to do the same.

Continuous data collection also facilitates assignment of enforcement resources based on occurrences of recorded weight violations, as used in Michigan and North Dakota.  Historical data from WIM systems can be used to focus inspections at locations where non-compliant and overweight trucks are known to travel.  Factors such as levels of truck traffic and frequency of overweight trucks at a site broken down by day and time of day are used to determine the most productive locations, days, and times for scheduling mobile enforcement teams.

One example of software used for enforcement purposes includes the data processing tool called “WIMCAT” (WIM Compliance Assessment Tool).  WIMCAT is used in Indiana and Minnesota to determine violations from raw data, to recommend optimal hours for enforcement, to facilitate estimates of damage from overweight vehicles, and to flag data anomalies.  In Indiana, such reports are issued on a weekly and monthly basis.  Another best practice example, Michigan’s Truck Weight Information System (TWIS), processes and analyzes truck weights collected at the WIM sites for use in targeting areas, days, and times of overweight activity.  TWIS will be enhanced with mapping and other new functionality as funds are available in the future.

Some states have enhanced their data management operations by developing enterprise-level WIM database management systems.  Both Minnesota and California are developing a data warehouse to manage their accumulating WIM data and make data accessible to more users.  Several states indicated that having a plan for managing and utilizing the WIM data is as critical as assuring the proper operation of the equipment.  However, states also reported difficulty in acquiring and maintaining resources for operating and maintaining data processing and management software.

The number of WIM systems used for statistics collection and planning varies considerably from State to State.  California has 190 WIM scales from which data is collected (the State has an additional 88 scales used for enforcement that do not provide data from all lanes).  Many states’ WIM systems originated as part of FHWA’s Strategic Highway Research Program (SHRP) or Long-Term Pavement Performance (LTPP) Program.  These programs, focused on pavement research, placed an emphasis on collecting locally- or segment-specific vehicle loadings.  States also have applied State Planning and Research (SPR) funds to deploy WIM systems used for traffic and pavement monitoring purposes.  Data from all these sites is collected continuously.  In some states, WIM data supplements classification and volume data collected from automatic traffic recorder (ATR) sites for design purposes.

4.1 Informed Placement of WIM Systems

In some states, the DOT will utilize its weigh-in-motion database to identify locations that regularly experience high incidences of overweight trucks.  It can then base its future installation of WIM systems according to this data, to more effectively enforce truck weight regulations.  This activity is generally referred to as informed placement.  Data collected as part of a State's traffic monitoring and pavement monitoring programs can be used to advance informed placement activities.  High incidences of overweight trucks at existing WIM locations are analyzed, and routes with expected increases in truck loadings are generally considered to be leading candidates for additional WIM installations.  New weigh stations are constructed for a variety of reasons, but patterns of weight violations observed or presumed to exist at a site play a role in locating a new facility.

A State can further the benefits of informed placement activities by using data from existing WIM sites to determine the sites’ suitability for preselection and enforcement activities.  Michigan used data from traffic monitoring WIM sites to decide at which of the locations real-time screening would be deployed.  At the outset, the Michigan State Police reviewed TWIS data gathered from traffic monitoring sites and envisioned the utility of using them for screening.  The State Police worked in concert with the Michigan DOT (which purchases and installs WIM systems and manages TWIS) to identify locations for wireless access to the WIM data for enforcement officers.  The two agencies formed a Commercial Vehicle Strategy Team consisting of five members from the DOT and four members from the State Police whose collaborative efforts include identifying locations for new WIM systems and “safe enforcement sites” that can be used by the State Police for weight and/or safety inspections in a safe environment, as well as locations where existing WIM systems can be enhanced for screening.

To date, Michigan has enhanced nine WIM systems for screening purposes by deploying a radio transmitter at the WIM location, a wireless air card in the patrol car, and specialized software on the officer’s laptop computer.  All existing sites that are given screening capabilities in Michigan are also upgraded to quartz piezo WIM technology devices.  After a WIM site in Michigan is upgraded and given screening capabilities, all traffic monitoring and enforcement data is continuously captured by TWIS.

States that reported plans to install new WIM systems intend to locate the new scales for enforcement uses (i.e., locations for screening, virtual weigh station, or weigh station), with concomitant data collection.  One State reported that WIM systems should be placed where they can “provide good information on what happens on the [road] system and for pavement decisions, and good locations for enforcement.”  Another State said, “WIM without enforcement does not make sense."

4.2 Preselection – Mobile Screening at WIM Sites

Preselection, or screening, is a method used to sort traffic to distinguish between legal vehicles and potential violators in order to focus inspection and evaluation on high-risk operators.  Screening is deployed to make more efficient use of enforcement resources.   Mobile screening at WIM sites is an example of preselection.  Virtual weigh stations, described below, are another example of preselection.  In a typical mobile screening environment, 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 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.

WIM sites used for mobile screening operations are not continuously monitored.  Enforcement personnel may conduct screening operations at a site according to a schedule or on a day-to-day basis, often as resources permit.  Mobile screening also can be distinguished from other enforcement-related WIM operations, such as mainline or ramp screening at weigh stations, which were previously described, and virtual weigh stations, which are described later.  States may call mobile screening by different names, including wireless access to WIM readings, “prescreening,” or even “virtual weigh station.”

In many cases, WIM systems chiefly used for data collection can be upgraded to contain mobile screening capabilities at relatively low cost.  Traffic monitoring functions have remained intact, while the addition of preselection capabilities is attractive to the State’s enforcement agency and optimizes the utility of the WIM equipment.  Several states (e.g., Indiana, Michigan, Minnesota) have upgraded one or more of their WIM systems to support preselection.  Two states, Minnesota and Indiana, have expressed their desire to eventually expand all of the State’s WIM systems into preselection sites, either for mobile screening or as virtual weigh stations.  Generally, existing WIM equipment can be utilized for screening when enhanced with wireless connectivity, specialized software, and user-selected data for viewing purposes.

When states upgrade (or retrofit) WIM sites for enforcement purposes, communication capabilities, computer operating systems, and data processing applications are all generally improved.  Other states, like North Dakota, designed all its WIM sites to support data collection and screening.  As a result, the State does not distinguish between WIM sites used for data collection and WIM sites used for screening.  Moreover, none of North Dakota’s 12 WIM systems were funded by SHRP or LTPP; rather, State construction funds supported the deployments.

Typical mobile screening sites require the following pieces of hardware:  a WIM scale or sensors, a roadside processor, wireless connectivity via Wi-Fi (wireless fidelity) or other short-range communication, generally using a transmitter at the WIM location and a receiver in the patrol car, and a laptop capable of handling data.  The laptop must have specialized software that can display the WIM data generated in real-time by trucks passing over nearby scales.  Visual and sound alerts help identify possible violators. 

One-person (vehicle) enforcement units are most commonly deployed at a typical mobile screening site.  The officer monitors the weights of passing trucks via laptop computer, intercepts suspect trucks, and weighs the trucks on portable scales at the roadside to record legally enforceable weights.  When two patrol vehicles are deployed, the first vehicle monitors WIM readings via laptop and communicates visual descriptions of suspect vehicles to a partner downstream.  The second enforcement unit then intercepts the suspect vehicles for roadside weighing with portable scales.  Two-person teams are likely to be deployed at higher volume locations.

Regardless of whether one- or two-person teams are deployed, a mobile screening operation has limitations.  Radio signals, commonly used to transmit the data from the WIM system, are effective for one-half to three-quarters of a mile as long as there is line-of–sight between the officer and the WIM scale or device.  This facilitates the visual matching of a vehicle with its associated WIM data. 

One State reported its enforcement agency was initially apprehensive about using truck traffic counts and WIM data because they felt the data might be skewed.  The concern with data quality was due to its perception that carriers may be avoiding WIM locations being used for enforcement-related screening.  However, the State no longer believes this to be the case.  Another State, which has not yet deployed any enforcement-related activity at a WIM site, believes that the character of traffic changes when enforcement is applied, affecting “typical” truck traffic patterns.

In order to visually verify the offending vehicle, inconspicuous enforcement may not be possible.  Because screening is a visual process, inclement weather and heavy truck volumes adversely impact operations.  Positioning of patrol vehicles also is limited by concerns about the officers’ safety in close proximity to moving traffic, as “good spots” for viewing trucks may not be the safest locations.  Michigan reported the following requirements for mobile screening:

  • Ability to collect and report accurate information;
  • Proximity to a safe place to weigh trucks;
  • Potential for overweight trucks; and
  • Commitment to deployment. 

States with mobile screening operations report considerable satisfaction with the deployments.  Mobile screening provides increased opportunity for enforcement by providing added capacity for resources, allowing for enforcement that is not disruptive to the travel stream, and guaranteeing more efficient delivery of enforcement actions through targeted intervention.  Michigan reported that during the first week of enforcement at the most recently deployed location (Interstate 75 near Vanderbilt), the officer on duty cited 10 overweight vehicles, nine of which he said he would never have been able to identify using visual indicators alone.  A best practice State, Michigan plans to install new WIM systems specifically for screening operations, rather than upgrading existing WIM sites used for traffic monitoring. 

Minnesota’s assessment is similar.  According to the State, mobile screening makes it much easier to identify overweight trucks.  Moreover, screening keeps the industry moving.  Carriers that have many trucks that are legally loaded are happy not to be stopped and weighed.  Minnesota has three elements in its weight enforcement program:  weigh stations, mobile patrols, and Relevant Evidence.  Mobile enforcement includes mobile screening at WIM sites.  Two WIM sites in northwest Minnesota, both on U.S. Highway 2 (mileposts 8 and 91), are used for screening by one mobile State Trooper.  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 from the WIM.  Traffic is light at both locations, which facilitates the visual identification of suspect trucks.  There is strong interest in expanding the use of WIM systems for enforcement purposes.  Concomitantly, Minnesota is “moving away” from fixed sites for weight enforcement because they are expensive to build and maintain.  Seven weigh stations exist in the State; of these, six are operational.

Relevant Evidence, which also is known as the civil weight program, is a uniquely Minnesota form of weight enforcement.   It allows State enforcement officials, under statutory authority, to examine weigh bills and issue civil penalties for overweight loads.  The weigh bill is “relevant evidence” of an overweight violation.   By law, all parties that weigh goods (e.g., receiving sites such as grain elevators, gravel and quarry operations, refineries, milk products plants, paper mills) must retain weight bills, bills of lading, and other freight documents for 14 days, and must allow access to enforcement officers (no search warrant is needed).  Civil penalties for excessive weight may be applied if the enforcement officer has inspected and copied the record within 14 days of the date the shipment was received by the party in possession of the record.  The program was established in 1980, and amended in 2002 to include the 14-day limit on civil penalties and a $10,000 maximum fine.  Currently, approximately 100 Troopers and Commercial Vehicle Inspectors of the Minnesota State Patrol are trained to conduct the civil weight operations.  According to the Minnesota DOT, the program works so well that nearly every year there is a bill before the State Legislature to change the law.

North Dakota’s assessment of mobile screening is that it is “great” and works well, but availability of staff to conduct the operations is an ongoing problem.  As indicated previously, all of North Dakota’s WIM sites were designed to support both data collection and screening.  Troopers position themselves by the WIM sites and screen trucks as they pass by, monitoring the WIM data that has been transmitted by radio communication to their laptop that displays the data and presents color or sound alerts to notify them of potentially overweight vehicles.  In North Dakota, the majority of trucks that are pulled over are weighed on portable scales, although six of the WIM sites are located in the vicinity of a weigh station.  WIM screening is conducted on a week-to-week schedule because of manpower constraints.  In a good example of “double duty” uses, the data collected by the WIM systems is used to assign enforcement resources according to the incidence of recorded weight violations.  North Dakota is interested in enhancing its screening operations by implementing a digital imaging system so photos of potential overweight violators can be sent to officers, relieving the dependence on visual association.  North Dakota, a leader in the advancement of “virtual WIM” systems, is the chair of the Virtual WIM Lead States Team of the Technology Implementation Group (TIG) of AASHTO.

California is very interested in deploying mobile screening to replace weigh stations.  Mobile officers of the California Highway Patrol are members of the Mobile Road Inspection Program, who are spread out on the mainline roadways (not freeways) and typically use visual indicators to select vehicles for weighing and/or inspection.  The Highway Patrol reported that these officers would be interested in conducting screening operations at WIM sites.  According to evidentiary information, states not contacted for this study also are interested in deploying mobile screening.  By adding screening functionality to existing traffic monitoring WIM sites, New Jersey will stop trucks for inspection in a selective rather than random manner.  Once a truck is stopped, the New Jersey State Police will determine if a full safety inspection should be conducted in addition to weighing.  Initially, 11 sites will be upgraded with wireless communications and new computer operating systems to allow them to be used for screening. 

Among the lessons learned from states’ deployments of mobile screening, it was observed that although screening can lead to more efficient use of resources, a full complement of size and weight enforcement officers is essential to support effective screening operations.  This is because personnel must be available to statically weigh suspect trucks on portable or semi-portable scales.  Moreover, systems that require human monitoring such as mobile screening are of limited value during staffing shortages.  In this vein, it was noted that the lack of automatic identification of vehicles suspected of being overweight severely limits the efficiency and effectiveness of roadside enforcement.

Generally, states consider mobile screening to be well worth the costs, especially when existing WIM systems are utilized.  One State reported $160,000 for deployment of four lanes of quartz piezo sensors, WIM controller, roadside cabinet, computer, radio frequency transmitter and receiver, and utilities.  Another State offered that only “limited incremental costs” are needed to upgrade a WIM site used for data collection to one used for enforcement as well.

4.3 Preselection – Virtual Weigh Stations

For purposes of this memorandum, mobile screening is distinguished from a virtual weigh station.  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.  While in use for enforcement purposes, however, both a mobile screening site and a virtual weigh station require human monitoring.

At this time, our definition of a virtual weigh station is as follows:

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.  Typically, one is located where a fixed weigh station would not be feasible for environmental or cost reasons.  For example, virtual sites can be located in urban areas more readily than fixed, staffed weigh stations.  They also may be located where a fixed, staffed site is not needed, but where violators are likely to travel.  Depending on the technologies present, virtual weigh stations provide at least the same information about a vehicle as does a traditional weigh station.

In virtual weigh station 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 this 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.  Instead of an officer located downstream performing monitoring and weighing functions, personnel viewing the WIM data and images at another location such as a central office or weigh station could dispatch nearby enforcement units to intercept and weigh suspect vehicles identified on the monitor.

At bypass route locations where vehicles frequently exit the main highway to avoid weighing at a weigh station, virtual operations can be integrated with the operations of the weigh station, allowing the enforcement agency to more effectively allocate their limited resources.  An officer on duty at the weigh station can monitor the virtual weigh station operations on a computer screen (that will include vehicle images and associated weight information) and dispatch another officer also located at the station to intercept a suspected overweight vehicle bypassing the weigh station facility.  Alternatively, an officer may be located downstream of the virtual weigh station and can be radioed to pull over the suspect vehicle. 

The virtual weigh station at Punta Gorda, Florida was deployed to evaluate the incidence of trucks bypassing the nearby weigh station.  Two WIM systems and four cameras were installed north and south of the weigh station to monitor trucks leaving Interstate 75, using U.S. Highway 41 (a parallel highway west of the weigh station), and re-entering the interstate.  The virtual weigh station elements are as follows:

  • WIM and camera on the northbound interstate exit ramp south of the weigh station;
  • Camera on the northbound interstate entrance ramp north of the weigh station;
  • WIM and camera on the southbound interstate exit ramp north of the weigh station; and
  • Camera on the southbound interstate entrance ramp south of the weigh station.

The virtual weigh station can reveal if trucks that leave the interstate, travel on Highway 41, and re-enter the interstate are bypassing the weigh station.  The camera takes a photograph of a truck leaving the interstate; the co-located WIM is used to determine if the truck is overweight.  On the other side of the weigh station, a camera takes a photograph of the truck entering the interstate (from Highway 41), which is compared to the photograph of the truck exiting the interstate.  The time between photographs is compared to determine if bypassing was likely.  For example, if the time between photographs is one hour, it is assumed that the truck had a legitimate reason (e.g., fuel or food stop) to exit the interstate and was not bypassing the weigh station.  Short durations arguably indicate bypassing.  Monitoring and evaluation are performed at the weigh station scale house.  Beyond its original objective of assessing the incidence of bypassing, the Punta Gorda virtual weigh station is used to identify overweight trucks, which are intercepted, weighed, and if warranted, cited for weight violation.

In Minnesota, line-of-sight limitations of mobile screening led to deployment of a digital camera as part of a demonstration project.  The digital camera allowed an officer to be located at a much greater distance from the site, affording lower visibility of enforcement activities.  Flexibility in the positioning of the patrol vehicle was mentioned by other states as a key benefit of digital imaging deployment at a virtual weigh station.  Furthermore, in areas with high truck volumes, a suspect vehicle can be identified by its photo integrated with its WIM record.

In addition to a WIM scale and a vehicle detection system, hardware requirements of a virtual weigh station include the following:

  • WIM controller that collects weight data and passes it to the computer in the roadside cabinet,, and triggers the camera;
  • Computer loaded with software that interfaces with the controller and camera, e.g., integrates the digital image with the WIM data;
  • Wireless cellular network to a file transfer protocol (FTP) or web server, or to the WIM cabinet through the Internet, to access the data and images;
  • Laptops loaded with specialized software capable of presenting weight information; and
  • Digital camera(s), which may be concealed (e.g., in the roadside cabinet) or visible (e.g., on a mast arm).

Associated software can vary in its degree of complexity depending on the user’s needs.  At minimum, images of the vehicles must be correctly associated with the corresponding weight readings.  A Remotely Operated Compliance Station (ROCS), such as the one at Sneads, FL, collects total vehicle weight, axle weights and spacings, dimensions, USDOT number, container number, speed, and sequential ID, and displays the data along with vehicle photos.  Indiana’s WIMCAT, previously described, estimates exceedances in gross vehicle or axle weight limits from the raw data.  The system also uses historical data to suggest optimal hours for enforcement, and produces data that can be used to estimate pavement wear and bridge damage.  The WIMCAT also features quality assurance and quality control (QA/QC) checks on the data, highlighting anomalous values.

A license plate reader (LPR) or USDOT number reader provides the virtual weigh station with digital image capture and identification through a digital camera or cameras augmented with specialized optical character recognition (OCR) software to isolate and identify specific characters and numbers making up a license plate number and/or USDOT number.  LPRs and USDOT number readers are forms of automatic vehicle identification (AVI).  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 LPR or USDOT reader can interface with a State’s Commercial Vehicle Information Exchange Window (CVIEW) to retrieve safety and credentials information associated with the vehicle identified automatically by its license plate or USDOT number.  Additionally, license plates can be searched in the National Crime Information Center (NCIC) or other database or list, further expanding the screening factors.  AVI deployment allows screening on safety, credentials, and criminal justice information as well as weight by associating WIM readings and can considerably reduce the time required to retrieve additional information about a suspect vehicle. 

Indiana soon will have installed three virtual weigh stations with typical camera systems.   The roadside computer software marries the WIM record with the vehicle image and transmits it via a wireless cellular network to an FTP site, where it can be accessed by authorized parties.  Downstream of the WIM site, an enforcement officer views the real-time WIM data linked with the vehicle photo on a laptop computer in the patrol vehicle.  With this information, the officer can pull the truck over for weighing and inspection.  WIMCAT, which is loaded on a computer in the roadside cabinet and determines violations from the raw WIM data, also can be used to recommend optimal hours for enforcement, facilitate estimates of damage from overweight vehicles, and flag data anomalies.  The State estimates the cost of retrofitting an existing WIM site (no new sensors) as approximately $30,000.  Indiana will also install quartz piezo WIM sensors at all new sites.  Future plans also include OCR deployment for automatic vehicle identification.  As stated previously, Indiana would like to use the entirety of its 50 traffic monitoring WIM sites for enforcement as virtual weigh stations.  None of the 50 WIM sites is located on a weigh station bypass route.  As part of the State’s long-range planning for weigh stations, which includes participation of the Indiana DOT and the Indiana State Police, it is likely that new WIM systems will be installed on “troublesome” routes and these WIM sites will serve as virtual weigh stations.  Weigh stations will be more effective in improving compliance, according to the State Police, when WIM technology is deployed on bypass routes.

Florida has deployed several virtual weigh stations, including a USDOT number reader at JAXPORT which supports a comprehensive vehicle information system for truckers that is capable for enforcement but is not currently used for this purpose.  Punta Gorda, where a camera system is employed, is used for enforcement, as described previously.  A third site, Sneads, was designed to test technologies and is used for demonstration and data gathering purposes.  License plate readers also are deployed at all of Florida’s weigh stations on the station ramps and at some of the State’s agricultural inspection stations at location of the inspection station building.

JAXPORT’s system (also called ROCS, as at Sneads) was designed to show drivers what their trucks weigh as they leave the container port.  This alerts them to the possible need for a permit if they exceed their established weight.  Despite Florida DOT’s concerns about overweight containers, weight violations have not been reported, only speed violations.  Truckers realize that the system is not used for enforcement, and they like it.  The ROCS architecture is the same for both JAXPORT and Sneads, although JAXPORT has more technologies and greater physical infrastructure.  Basically, the system has two components:  capture systems in the field connected to the main computer, and query and display functions provided by the central server and interface that integrate all the data.  ROCS is “self-healing,” so if the central server goes down, all files are saved.  A primary objective has been to ensure that all the technologies and computers work together.  These elements include the following:

  • WIM quartz piezo sensor in the right-hand lane of traffic;
  • Dimensioning sensor that provides height and width, with radar to provide length;
  • Low resolution camera for vehicle images;
  • USDOT number camera and computer;
  • Container number camera and computer;
  • PTZ (pan, tilt, and zoom) camera to remotely view the area;
  • Dynamic message sign that displays the truck’s weight; and
  • Weather station.

Real-time enforcement screening on the vehicle parameters produced by the available sensors and technologies could be accomplished by accessing the data through wireless Internet access. As stated, neither the JAXPORT nor Sneads sites are used for enforcement.  The estimated cost of ROCS at JAXPORT was $250,000 (with an additional $100,000 for the mast arm and pole).

The Sneads virtual weigh station is used to demonstrate technologies and collect data.  ROCS at this location captures speed, overall weight, axle weights, and three photographs of the vehicle, and stores the information in a database.  The Sneads weigh station is nearby.  At the weigh station, static weights of individual trucks can be measured that can be compared with WIM readings.  The Sneads weigh station supports PrePass electronic screening.  The high-speed weigh-in-motion device and roadside digital camera image capture system of the Sneads virtual weigh station are not integrated into the weigh station, or PrePass, operations.

Florida’s agricultural inspection stations support a unique suite of advanced technologies.  Twenty-three inspection stations are operated by the Florida Department of Agriculture and Consumer Services (DACS), through its Office of Agricultural Law Enforcement.  By statute, all trucks must enter an agricultural station and submit for inspection.  The agricultural inspection station at Yulee on Interstate 95 in Nassau County is one of 17 stations equipped with a license plate reader.  The LPR extracts the plate number and transmits it to the Florida Crime Information Center (FCIC)/NCIC to check for stolen equipment, Amber Alerts, warrants, etc.  A container reader utilizing OCR software also has been deployed, which reads the container identification number from the container and passes it to DACS’ central server in Tallahassee.  A container will appear in the Tag Recognition System if there is an alert on the container.  The vehicle and cargo inspection system (VACIS) deployed at the Yulee agricultural inspection station is a gamma ray imaging system that uses radiographic images to help trained inspectors examine the closed contents of trucks, containers, and cargo for hidden compartments containing contraband.  VACIS is deployed at the four Interstate agricultural inspection stations, located in Suwannee, Hamilton, Escambia, and Nassau Counties.

Yulee is also one of six “AgPass” sites in Florida (two at each of the agricultural inspection station locations on Interstates 10, 75, and 95).  PrePass Ag, as it also is called, is a partnership of PrePass and DACS that allows eligible enrolled commercial carriers to bypass the six inspection stations in the same way they bypass PrePass-equipped weigh stations (i.e., through the use of a transponder).  Only carriers that do not haul dedicated agricultural cargo are approved by DACS for the program.  Carriers’ bills of lading are provided to DACS electronically by PrePass Ag.  On Interstate 10 the Florida DOT weigh station and the DACS agricultural inspection station are closely located.  Trucks without transponders must pull in to both stations.  On the other hand, trucks enrolled in both PrePass and PrePass Ag are eligible to bypass the stations.

California deployed a prototype virtual weigh station, including LPR, at Cordelia.  The Cordelia virtual weigh station is located on eastbound Interstate 80, halfway between Sacramento and San Francisco, at a point of congestion that is not easily or cost effectively bypassed by commercial vehicles.  It is located in the same place as the PrePass transponder reader in advance of the Cordelia vehicle inspection station.  PrePass uses the WIM data collected at this location to help determine the eligibility of enrolled vehicles to bypass the inspection station.

The Cordelia virtual weigh station’s in-pavement technical components include a bending plate WIM scale, a vehicle detection system, and a camera triggering system.  Data integration is performed by computer systems located in three roadside cabinets.  The first cabinet contains the control systems for the side fire camera and license plate camera, as well as the OCR computer; in the second cabinet, digital images are converted into picture images, vehicle images are matched with weight measurements, weight limits are checked and weight compliance is determined, data are formatted for transmission and remote viewing, and weight data only is transmitted to a PrePass computer also at roadside; the third cabinet holds the PrePass computer.  The PrePass computer integrates the vehicle identification information obtained from the vehicle’s transponder with the WIM data and sends the results to the PrePass computer at the Cordelia inspection station, which verifies safety and credentials status and subsequently notifies the driver to bypass the inspection station or pull in for inspection.

Considerable discussion has centered on the need for OCR capability, and it is unclear if future enforcement-related WIM sites in California will support OCR.

The first virtual weigh station in Kentucky was installed in 2003 and utilized quartz piezo WIM sensors and a digital camera system.  The digital images of the truck could be used by personnel at a nearby weigh station to read the USDOT number.  The site is no longer in operation.  Kentucky has since deployed virtual weigh station technologies such as license plate and USDOT number readers at operational weigh stations, as part of ongoing research, testing, and development efforts.  The technologies are components of the Integrated Security and Safety Enforcement System (ISSES), which is deployed at three of Kentucky’s weigh stations.  ISSES includes a license plate reader, a USDOT number reader, radiation portal monitors, and an infrared camera for detection of brake deficiencies.  The technologies operate within the weigh station after the truck has been weighed on the ramp WIM and its dimensions scanned by the height, width, and length detector.  The weigh stations also are instrumented to provide electronic screening capabilities, including bypass privileges for eligible NORPASS carriers.  As situated, the ISSES technologies are too close to the scale building to be practical for automated screening, and as a result, human monitoring and data entry (keying in of the license plate and USDOT numbers) are still required.  The LPR and USDOT number reader are not currently being used for enforcement purposes at these locations.  Kentucky reports that the individual ISSES technologies work well, but it has been a challenge to integrate them into one system with one user interface.  

Kentucky plans to incorporate the LPR and USDOT number reader into an automated ramp screening system for a weigh station.  This system will use weight data from the ramp sorter WIM along with the license plate number and/or USDOT number to access the Kentucky CVIEW and make an automated screening decision.  This scenario will be the prototype for Kentucky’s “next generation” virtual weigh station that will include an LPR and USDOT number reader linked with the State’s CVIEW, at an unstaffed site on a non-Interstate route.  The goal is to continuously monitor trucks that do not routinely pass through a weigh station.

Washington State indicated its intention to deploy virtual weigh stations, which would include LPR, at one or more locations in the eastern part of the State.  Mississippi intends to pilot a LPR-equipped virtual weigh station at one or two sites.  Mississippi has numerous WIM sites throughout the State that are used for traffic monitoring and planning purposes.  The CVISN team is examining multiple sites to assess their suitability for screening operations.  In some cases, a WIM site may be used for mobile screening, whereby the enforcement officer at the WIM uses weight data displayed on the laptop computer to screen passing trucks.  The ultimate step is to implement virtual weigh station capabilities in the form of a license plate reader.  One promising location is a heavily traveled route (Highway 82 near the Port of Greenville on the Mississippi River) that does not support a weigh station.  This location originally was considered for a traditional weigh station.  The pilot project may be expanded to include an additional virtual weigh station at a location where trucks routinely bypass the weigh station, specifically on Interstate 10 .  States not contacted for this study, such as Montana and Colorado, evidently also plan to deploy virtual weigh stations.

It was observed by a best practice State that the more technologically complex the project is, the more essential the teamwork becomes among project partners.  In most cases, more than one agency is involved, and close planning is needed to assure that all parties’ objectives and requirements are met by the project.  Different “pieces” of the project (e.g., WIM, LPR, container number reader) may have different affected stakeholders (who may be within the same agency), each of whom has a different reason for being interested in the data that is produced.  Furthermore, each technology may have multiple stakeholders.  Needs of all stakeholders must be taken into consideration when planning and selecting technologies, and working as a team is arguably the most effective way of achieving this.

All states commented on the cooperative relationship that has to be in place, or built, to support the successful deployment of roadside technologies.  In Michigan, cooperative efforts between the DOT and the State Police (meeting as the Commercial Vehicle Strategy Team) determined the best locations for all WIM systems, both for traffic monitoring and screening purposes.  North Dakota reported that collaboration between the DOT and the Highway Patrol in planning and constructing WIM sites for dual purposes was essential for success.  In the late 1990s the State Police and the DOT collaborated on the deployment of Indiana’s first WIM site that was enhanced for real-time screening.  Today, the two agencies participate in a committee for long-range weigh station planning, which develops weight enforcement strategies involving virtual weigh stations as well as weigh stations.

One State said plainly that the State’s enforcement agency must “make partners” with the DOT in order to obtain the tools it needs for enforcement.  Without the DOT’s help and cooperation, the tools will not be made available to enforcement personnel.  Finding the common ground, such as improving commercial vehicle safety, and in so doing, improving overall highway safety, is the first step in developing a partnership.

States also mentioned the importance of support from the motor carrier industry.  To the extent that activities such as mobile screening and virtual weigh stations “take the bad guys off the road,” make the roads safer, and level the playing field between carriers that are safe and legal, and those that are not, State trucking associations can be strong advocates and allies.  Mississippi reported that the trucking association recognizes the value of virtual weigh stations in addressing and correcting problems with overweight trucks on routes with heavy commercial vehicle traffic and thin enforcement resources.  Other states such as Washington and Kentucky commented on the strong support their CVISN program has received from the State trucking association.  Support from the trucking association in these and other states involves participation in planning processes and marketing programs to motor carriers.

4.4 Summarized Information on Usage of Technologies

Information on WIM, DSRC, and camera/OCR technologies that was gathered in the task data collection effort is presented in template format following page 26.  Summaries of functionality, technical requirements, locations, advantages and disadvantages, enhancements, and lessons learned are available for programs and systems that utilize WIM, DSRC, and camera/OCR technologies in the states participating in this study (listed on the next page).  Where a description or entry is unique to a State, the State is identified.  Otherwise, statements are generally applicable to the participating states.  

The “template” was populated almost exclusively with information gathered from the participating states.  Where cells are “empty,” states did not provide information.  Limited information from other sources was included for clarification.  Acronyms used in the report or template are explained in Appendix A.

Participating States


Contact Name

Contact Information


Joe Crabtree



Randy Woolley



Mike Akridge

850- 410-5607


Gene Halverson



Randy Coplin



Tom Melville


North Dakota

Tom Bold



Anne Ford



Nan Tarlton


previous | next
Office of Operations