George Novenski, Wisconsin Department of Transportation
Bill McCall, Iowa Department of Transportation
Dick Stehr, Minnesota Department of Transportation
St. Paul, MN
March 1989

The Third National Conference on WIM was attended by representatives from all 50 states and eight foreign countries. Presentations and demonstrations clearly revealed wide spread acceptance and use of WIM for both enforcement of vehicle weight laws, pavement design, and management.

This conference looked forward toward wide deployment of WIM made possible by low cost WIM sensors; toward expanded use of WIM data for enforcement planning, screening, and possibly even prosecution of overweight vehicles; and toward integration of WIM with other technologies as an accepted, powerful tool for states to effectively manage the highways.

The immediate prospects for WIM are exciting, the future outlook is bright, and the applications seem endless! We thank all of the participants, speakers, and equipment suppliers who helped make this an exciting and successful conference. A special thank you to the Federal Highway Administration whose sponsorship and support made it possible.

Following is a list of the papers presented at the conference. Abstracts are included where available.

Applications and Future Directions
Richard Morgan, FHWA, Washington, D.C.

National Uniformity (no paper submitted)
C. Michael Walton, University of Texas

During the summer of 1987 the Maine D.O.T. Technical Services Division conducted an evaluation of those WIM systems that could be made available for testing. The following WIM systems were available and tested: 1) Golden River: Capacitance Pad; 2) CMI/IRD System: Load Cell Scale; 3) Bridge Weighing Systems: Clamp-on Gauges; 4) PAT System: Bending Plate; 5) Streeter Richardson: Bending Plate; and 6) Streeter Richardson: Capacitance Pad.

Comments made in this paper about the operational characteristics of the various systems are the result of observation of their behavior during this study. The manufacturers have since made some changes to several of the systems which may result in improvements in the operation of the currently available units.

Factors that Affect the Accuracy of WIM Systems
Clyde E. Lee, University of Texas at Austin

A number of different systems for weighing highway vehicles in motion have been developed during the past three decades. These systems, called weigh-in-motion (WIM) systems, have generally been used by public agencies for 1) collection statistical traffic data, 2) aiding traffic law enforcement, or 3) actual enforcement. There has always been concern about the accuracy with which a WIM system can estimate the weight of a vehicle as well as about the accuracy with which weight needs to be determined for each of the applications mentioned. The purpose of this paper is to identify the factors that potentially act and interact to cause inaccuracy and to discuss the relative importance and magnitude of some of these factors.

WIM System Accuracy
Wiley D. Cunagin, Texas A & M University

This paper addresses the measurement and expression of the accuracy of WIM systems. The subject of WIM accuracy is very important yet frequently misunderstood by both the vendors and users of WIM systems. As a result, it has often been difficult to compare the specifications published by vendors or to determine which WIM system is most appropriate to a specific application. Consequently, recent studies have addressed the need for better defined measures of accuracy and methods of applying them to WIM systems. These are presented in this paper along with a discussion of the problems associated with measuring the accuracies of WIM systems.

Weigh-In-Motion (WIM) Standardization: Stimulation, Development & More Stimulation
Lawrence E. Hart, Rainhart Company, Austin, TX

GENERAL SESSION -- APPLICATIONS OF WEIGH-IN-MOTION
Colorado's Applications of Weigh-In-Motion Data for Highway Planning
Tom Talmadge, Colorado Department of Highways

Dynamic Forces Versus Static Weights -- Highway Design
Herbert F. Southgate, Kentucky Transportation Center

This paper addresses the evaluation of a Golden River WIM system in Kentucky. Specific issues discussed include calibration factors, WIM versus static weighing, vehicle velocity, pavement design, and fatigue calculations.

Pavement Management and the Pavement Policy
William A. Nostrand, Jr., FHWA, Washington, D.C.

Demonstration Project No. 76: Automated Traffic/Truck Weight Monitoring Equipment (Weigh-In-Motion)
William A. Nostrand, Jr., FHWA, Washington, D.C.

The objective of this project is to provide State Highway Administrators, pavement designers, weight enforcement personnel, and planners with an understanding of the various types of WIM technologies, their accuracies and reliability, installation costs and procedures, the approximate costs of each and their maintenance requirements, the appropriate application of each, limitations to their use, and cost-effective methods of coordinating WIM data collection to support a multitude of users.

Applications of Weigh-In-Motion in SHRP's Long Term Pavement Performance Study
Neil Hawks, Strategic Highway Research Program, Washington, D.C.

The Strategic Highway Research Program (SHRP) is a five year $150 million effort to achieve rapid progress in highway technology. SHRP includes four technical research areas: asphalt, pavement performance, highway operations, and concrete/structures.

The Long Term Pavement Performance (LTPP) program includes two type of studies: 1) General Pavement Studies (GPS) and 2) Specific Pavement Studies (SPS) and is planned as a 20 year effort. The specific objectives of the LTPP study are: 1) evaluate existing design methods; 2) develop improved design methodologies and strategies for the rehabilitation of existing pavements; 3) develop improved design equations for new and reconstructed pavements; 4) determine the effects of loading, environment, material properties and variability, construction quality, and maintenance levels on pavement distress and performance; 5) determine the effects of specific design features on pavement performance; and 6) establish a national long-term pavement data base to support SHRP objectives and future needs.

Pennsylvania's Use of Weigh-In-Motion in its Weight Enforcement Program
Frederick R. Juba, Pennsylvania Department of Transportation

Georgia's Experience with Weigh-In-Motion as a Screening Device
Jack Williams, Georgia D.O.T.

Legal Aspects of Overweight Assessments in Georgia
Jack Williams, Georgia D.O.T.

Use of Civil Procedures as a Tool in Weight Enforcement
Jeff Bilcik, Minnesota Attorney General's Office

PAVEMENT MANAGEMENT WORKSHOPS:

Data Collection Traffic Data Collection Procedures, North Dakota Highway Department
Dennis E. Jacobson

The Bridge Weighing System and the Traffic Monitoring Guide--the North Carolina Experience
E. R. Shuller, NCDOT

The North Carolina Department of Transportation (NCDOT) has operated a truck weighing program to obtain axle and gross weights, axle spacing, loading practice, and related data since the late 1930s. In that time there have been years when data collection was suspended and occasional changes in frequency or length of sample sessions. The most significant change occurred in 1986, when the traditional static wheel scales were discarded in favor of weighing-in-motion (WIM).

The focus of this paper is on the goals NCDOT hoped to achieve with WIM, the selection of equipment, the selection of the sample in compliance with the Traffic Monitoring Guide, and finally, a brief comparison of the data collected with the new technology to that collected with the old.

Wisconsin Revised Truck Weight Study
Paul P. Stein, Wisconsin Department of Transportation

In 1983 the Wisconsin Department of Transportation (WISDOT) implemented a truck weight data collection program utilizing a high speed Bridge Weigh-In-Motion (BWIM) system. This program called for data collection at 21 locations on seven functional highway systems throughout the state. Duration of site operations was to be determined by attainment of predetermined truck type samples. These goals, and the allocation of sites between highway systems, were determined by statistical analysis of Gross Vehicle Weight (GVW) data collected at permanent scales between 1980 and 1981. Additional guidelines were established to collect day, night, and seasonal data at a control station on each highway system.

In 1986 WISDOT began a study of the data collected to determine the adequacy of the program, the validity of the data collected, and to make recommendations for revisions in the program in light of the results of the analysis and the then recently published FHWA Traffic Monitoring Guide. This presentation focuses on results of that study, along with the findings of a companion study on the population of overweight trucks in Wisconsin.

Network and Project Data Collection
William E. Barrows, Illinois Department of Transportation

Network and Project Data Collection
Keith E. Longenecker, Idaho Transportation Department

Remarks on the Feasibility of a National Heavy Vehicle Monitoring System
Lance Grenzeback, Cambridge Systematics Inc. Cambridge, MA

PAVEMENT MANAGEMENT WORKSHOPS: Data Analysis and Use

Pavement Management Workshop, Data Analysis and Use
Dave McElhaney, FHWA, Washington, D.C.

Tennessee Weigh-In-Motion
Bonnie H. Brothers, Tennessee DOT

This paper presents an overview of Tennessee's experience in implementing the Traffic Monitoring Guide. The Tennessee DOT has progressed from the labor-intensive, static loadometer studies, to weigh-in-motion (WIM) equipment, which abundant data on truck weights can be obtained much more cost-effectively. The paper also summarizes how WIM data has been analyzed and used as a planning tool by establishing trends in highway usage in Tennessee.

Importance of Trucks in Pavement Management
Barna Juhasz, James Gruver, Roger Petzold, Richard Backlund, FHWA

With the completion of the Interstate System, attention has shifted from building a highway network to improving, operating, and maintaining the highway system. Thus, we have moved from construction to management of our highways in a cost-effective manner. Pavement management systems are being established to "assist decision makers in finding optimum strategies for providing, evaluating, and maintaining pavements in a serviceable condition." This systematic approach is needed to improve management of this nation's large existing investment in pavements and to help make better use of limited funds.

The purpose of this paper is to discuss: 1) why truck movements on the highway system are important to pavement management; 2) how to determine where trucks are moving on the highway system now and in the future; and 3) how to determine the effect of trucks on pavement performance now, in the future, and in the past.

Use of WIM in South Dakota (no paper submitted)
David Huft, South Dakota Department of Transportation

Use of Weigh-In-Motion Data for Pavement Design--a Preliminary Examination of ESAL Calculation Using WIM Data
Mark E. Hallenbeck and Tu Cheng Kuo, Washington State Transportation Center

This paper examines the use of weigh-in-motion (WIM) data for calculating equivalent standard axle load (ESAL) values which are an important factor in pavement design. More specifically, it examines the differences to be expected between data collected with WIM and static weights. It then describes how these theoretical differences impact the calculation of ESALs. A methodology is presented to adjust the WIM data for the expected differences between WIM and static values. The preliminary findings of a test of this procedure are examined, conclusions are drawn, and future research is suggested.

Theory indicates that ESAL values calculated from WIM data should exceed ESAL values from static weights. The cause of these differences is vehicle motion, which is a function of vehicle load, vehicle suspension and road characteristics. In theory, the greater the vehicle motion, the greater the over-prediction of ESALs by WIM equipment, provided the WIM equipment is correctly calibrated and functioning.

However, when a limited set of actual WIM and static weight data was examined, the phenomenon of ESAL over-prediction was often overshadowed by inaccurate WIM data produced by poorly calibrated equipment and other problems. That is, ESAL calculations were affected by problems with the data to a greater extent than they were affected by random "dynamic" effects.

Insights From Weighing-In-Motion -- Adjustment of Short Term WIM Data to AADT, Dynamic Weights of Tandem Axles, and Overestimation of ESAL Factors
Curtis Dahlin, Minnesota D.O.T.

Minnesota's first continuously operating WIM system was installed in 1981. Since that time MN/DOT has installed them at three other data collection sites. Analysis of the data from those sites has led to several important observations and discoveries which this paper addresses: 1) adjusting short term truck traffic data to Annual Average Daily Traffic (AADT); 2) dynamic weights of tandem axles; and 3) overestimation of ESAL factors.

An Overview of ESAL Estimation and Forecasting for Pavement Design
Bruce Aunet, Wisconsin Department of Transportation

This paper will attempt to provide an overview of some of the issues involved in equivalent single axle loading (ESAL) estimation and forecasting for pavement design. Numerous factors potentially affect the selection of the thickness of a pavement structure and the types of materials and pavement used (shown in Exhibit 1). Much is known about some of these factors, such as material limitations, for example, yet little is known about others, such as weather and climate related environmental stresses. And while the pavement damage caused by increasing truck tire pressures and particularly dynamic forces and uneven tandem axle load distributions may be substantial, the effects have generally not been added into ESAL factors. While it is important to be aware of the larger picture, this paper focuses on the issues involved in estimating and forecasting the number of trucks, the vehicle or truck mix, and the average ESAL factors per truck type that make up total cumulative ESALs (over the design life).

WEIGHT ENFORCEMENT WORKSHOPS: Strategic Planning and Port-of-Entry Weigh Station Design

Summarization of Workshop on Weight Enforcement -- Planning, Operations, and Weigh and Inspection Station Design
John F. Grimm, FHWA, Washington, D.C.

Remarks on WIM as an Enforcement Tool
John R. Bailey, Arkansas Highway Police

Designing Weight and Inspection Station
A. F. Corbin, South Carolina Highway Patrol

New Strategies for Statewide Programs (Virginia's Perspective)
R. M. Ketner, III, Virginia D.O.T.

Planning for Enforcement Operations
Marsha Wiley, Wisconsin State Patrol

Weigh and Inspection Station Design, St. Croix Weigh Scale, Lakeland, MN
Calvin D. Karl, Minnesota State Patrol

The Metamorphosis of Weight Enforcement Strategies in Oregon
Milan Krukar and Ken Evert, Oregon D.O.T.

Over the years, enforcement strategies in Oregon have evolved to meet economic changes, regulations, and accommodate new technology. This paper examines Oregon's weight enforcement strategies in light of past and current requirements, and describes strategies designed to meet future needs and technology.

WEIGHT ENFORCEMENT WORKSHOPS: Operations and Compliance
The Automation of the Woodburn Southbound Port-of-Entry on Interstate 5
Milan Krukar and Ken Evert, Oregon D.O.T.

The Woodburn Port-of-Entry (POE), located on Interstate Highway I-5, is the busiest POE in Oregon. It has one weigh-in-motion sorter system and two electronic static scales, and is operated around the clock, seven days a week. A minimum of 2,000 trucks pass through the facility during a 24-hour period. During peak periods, over 3,300 trucks per day pass through the POE; 150 to 200 trucks may pass during a peak hour. The Woodburn POE was designed to handle an average of 1,700 vehicles per day with peak days of 2,200 to 2,300.

The purpose of this paper is to describe the automation of this POE in order to minimize the Weighmaster and PUC tasks; improve weight, size, and safety enforcement; provide more data for planning and design purposes; and save manpower and time for the State and the trucking industry. This paper describes the hardware and software, system operation, data obtained, benefits, limitations, and future goals.

Remarks on the Feasibility of a National Heavy Vehicle Monitoring System
Joseph R. Stowers

Traffic Impacts of Establishing Permanent Weigh Stations
Curtis Dahlin, Minnesota D.O.T.

Bridge Weigh-In-Motion System as an Enforcement Tool
David A. Bochenek, Maryland State Highway Administration

Minnesota's Relevant Evidence Law
Peter J. Gibson, Minnesota State Patrol

Minnesota's Relevant Evidence Law requires by statute that businesses who weigh goods before or after unloading or a person who loads or unloads goods on the basis of liquid volume measure, shall keep a written record of the origin, weight, and composition of each shipment, the date of the loading, the name and address of the shipper, the total number of axles on the vehicle or combination, and the registration of the power unit. The Relevant Evidence Law enables State Troopers to initiate overweight cases without detecting or witnessing a violation. This paper discusses the history of the program, the procedures involved in case investigation, and its advantages and disadvantages.

CLOSING GENERAL SESSION

Tricks of the Trade
George J. Novenski, Wisconsin Department of Transportation

Site Specific Load Models for Bridge Rating
W. David Liu, C. Allin Cornell, and Roy A. Imbsen, Imbsen & Associates, Inc., Sacramento and Portola Valley, CA

This paper describes briefly the modern reliability-based Load and Resistance Factor Design (LRFD) methodology to account for the uncertainties in load and strength variables. Specifically for site, specific load models, the authors want to identify the sources of the total uncertainty in extreme load effects and the data needs to reduce them. A large database of truck loads has been assembled from FHWA, Wisconsin, Florida, and Illinois WIM studies, including over 220,000 trucks. Results of statistical analysis of these load data and the implication to load model development are discussed. Several different ways to increase the information of local, site-specific loading are suggested. The authors hope that through discussions with other data users and data collection agencies, unbiased WIM truck load data can be directed toward bridge loading applications.

Calibration of Weigh-In-Motion Systems
J. M. Zuieback, J. D. Bailey, and G. D. Wonacott

This paper summarizes the results of an FHWA sponsored combination analytical and experimental project designed to meet the objectives listed above. the project consisted of two sets of field studies to collect the data to meet the objectives: 1) statistical comparisons of WIM and static axle weights, and 2) tire-pavement force measurement experiments using specially instrumented vehicles. A dynamic simulation model was developed and utilized to identify the key influential vehicle, roadway, and operational parameters to guide the experimental design. Chapter 2 summarizes the results of dynamic simulation analysis and Chapter 3 describes the two field study programs performed. Recommendations are found in Chapter 4.

WIM: The California Experience
John Van Berkel, Jr. California Department of Transportation

Evaluation of a Weigh-In-Motion (WIM) Device at the Pavement Testing Facility
D. M. Freund and R. F. Bonaquist, FHWA, McLean, VA

A GK Instruments piezoelectric weight and classification system has been undergoing field testing in Iowa and Minnesota under Demonstration Project 76. The Demonstration Projects Division and the Pavements Division extended the project to include a series of controlled tests at the PTF/ALF located at the Turner-Fairbank Highway Research Center. The system was installed in May of 1988 and tested until October.

The original experimental plan called for a factorial design to determine the accuracy of the system under changing loads, tire pressures, and transverse loading locations. As several modifications had been made to the signal translation unit to permit it to accommodate the ALF's unicycle loading patter, the plan was altered to concentrate on the output voltage signals themselves instead of the translated weight and classification readings.

There was no systematic pattern to calibration factors determined at different temperatures under constant weight. The source of this variation could not be determined, however, three potential sources have been identified.

Voltage data were collected directly from the piezo cable sensors instead of using the translated weight and classification readouts. These direct voltage plots have been quite consistent at constant loads, and have also shown systematic variation with changes in load. A second series of tests at different tire pressures showed variability similar to that observed in the early calibrations. A third series of tests at combinations of loads and tire pressures which provide a constant tire contact footprint appear to indicate that the system may be sensitive to the unit load as well as to the total load. This leads to concern that different combinations of loads and tire pressures may not be properly weighed.

The tests performed have provided a unique picture of the operation of this device. Use of the ALF to apply constant repeated loads and variable loads and tire pressures has been invaluable in assessing the WIM device. The testing was somewhat limited by the need to operate the ALF continuously over the planned time period for the pavement performance experiment.

Future Weigh-In-Motion (WIM) Technologies
Peter Davies and Fraser Sommerville, Castle Rock Consultants, Leesburg, VA

This paper contains an overview of current and upcoming WIM developments in the U.S. and overseas, concentrating primarily on the field of enforcement. The first section of the paper provides a brief outline of piezo-electric technology, which has been incorporated in the piezo WIM sorter system under evaluation in England. Some background information on UK truck weight enforcement practice has also been included. Details of the two-lane piezo WIM system are presented, including the sensor array, site layout, method of operation and system output. Tests carried out with the system are described, for which results will be available next year.

The final part of the paper seeks to take a longer-term look into the WIM crystal ball, including a discussion of two areas currently attracting the attention of the WIM fraternity: output formats and calibrations methods. Self-calibration, now becoming more widely accepted, is also covered.

Last Modified: November 2007

Maintained by: traffic@nmsu.edu

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