Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications (2020)

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4 Characterization of vehicle loads is a critical input for the design and management of trans- portation structures and systems. The advent of automated means to collect WIM data has provided for site-specific, per-vehicle data in lieu of estimation. Although DOTs are required to submit WIM data to the Federal Highway Administration (FHWA) as part of their traffic moni- toring programs, some agencies are using actual load data as a tool for various applications and decision making. Uses of WIM data, beyond federal reporting requirements, include pavement design, bridge design, asset management, load rating, commercial vehicle weight enforcement support, and freight planning and logistics. Objective The objective of this synthesis is to document how DOTs use WIM data for asset design and management, weight enforcement support, and freight logistics. This synthesis investigated the use of WIM data by DOTs in support of weight enforcement, but did not directly engage weight enforcement agencies. The synthesis identifies the use of WIM data as a tool to support decision making, including how WIM data are incorporated into these areas of application: • Pavement design • Pavement management • Bridge load ratings • Bridge management • Weight enforcement support • Freight planning and logistics The synthesis also documents impediments to using WIM data as a tool, knowledge gaps, and research areas that can potentially address those gaps. Method Information was gathered through a literature review, a survey of DOTs, and interviews with selected agencies for case examples. Literature Review A review was conducted of uses of WIM in these areas: • Pavement design, bridge design, and asset management and load rating • Commercial vehicle weight enforcement support • Freight planning and logistics C H A P T E R 1 Introduction

Introduction 5 DOT Survey A survey was developed to determine the state of the practice of WIM at transportation agencies. The survey asked about equipment, calibration, quality control, both standard and innovative uses of WIM data, identification of WIM data users, and impediments to the use of WIM data. The survey request was sent to all 50 state transportation agencies in the United States, 6 Canadian provincial transportation agencies, and NYCDOT. In this synthesis, we refer to all such agencies as departments of transportation. The U.S. state DOT response rate was 90%, with 45 of the 50 DOTs responding. The total response rate from all DOTs requested to complete the survey was 91.2%. In some cases, more than one person responded from an agency, according to their area of expertise. These responses were consolidated to produce one agency response for use in this study’s analysis. As weight enforcement was out of the scope of this study, the focus was on getting responses from DOTs and not commercial vehicle enforcement agencies. No commercial vehicle enforcement agency or law enforcement agency participated in the survey. Case Examples Using the survey responses and identified criteria to obtain a diversity of states, five DOTs were selected for follow-up with phone interviews to gain a greater depth of understanding of that DOT’s WIM data collection and use. Questions were developed for each individual DOT to augment information obtained from the survey. Definition of Terms Following are definitions of the terms this synthesis uses. Weigh-in-Motion System or Station A WIM system encompasses the sensors and other components that estimate the gross vehicle weight of a moving vehicle as well as the portion of this weight that is carried by the tires of each wheel assembly, axle, and axle group on the vehicle. The system allows other traffic data to be collected or calculated, such as speed, lane of operation, date and time of passage, number and spacing of axles, and classification (according to axle arrangement) of each vehicle. The data can be stored or transmitted to a remote location for aggregation and data analysis. A WIM system at a specific location can be called a WIM station. WIM Network A WIM network is the set of WIM stations a DOT maintains in order to gain weight and other traffic information about vehicles using their transportation infrastructure. WIM Program A WIM program is an initiative to use WIM network data to support various infrastructure design, management, and planning goals.

6 Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications Virtual Weigh Station (VWS) VWS is a WIM system augmented with additional sensors and cameras that may include over-height detection and image capture of license plates or DOT numbers for identification. The definition is flexible to allow for inclusion of various sensors, cameras, and lighting. VWS is unattended and allows for remote real-time monitoring. Bridge Weigh-in-Motion (B-WIM) B-WIM is instrumenting a bridge with sensors, usually strain gauges, to monitor bridge member deflections in order to estimate the weight of the vehicle producing the deflections. B-WIM is out of scope of this synthesis, although it is mentioned in the literature review. Background WIM systems arose from the need to know axle weights. This knowledge was essential to the development of the interstate system and remains a crucial component of infrastructure maintenance, even as technology and data needs have evolved. The Need for WIM To understand the evolution of WIM, it is helpful to understand why DOTs need to know the weights of vehicles using a roadway. Historically, vehicle weight regulations in various states were enforced via weight measurements taken on static scales; the need for a more advanced measurement system (i.e., WIM) can be traced to the U.S. government’s plan to build a system of interstate highways with public money. The origin of the Interstate Highway System (IHS) can be traced back to Lt. Col. Dwight D. Eisenhower volunteering to participate in the U.S. Army’s first transcontinental motor convoy from Washington, D.C., to San Francisco in 1919. During this trip Eisenhower realized the value of good highways. The convoy took 62 days to cross the country and encountered mechanical problems, vehicles stuck in mud and sand, equipment breaking through wooden bridges, and slippery roads (Weingroff, 1996). That same soldier became a five-star general and Supreme Commander of the Allied Expedi- tionary Forces in Europe in World War II and saw the value of the high-speed, well-developed road system in Germany. Then, as President of the United States (1953 to 1961), Eisenhower sought to bring those ideas to reality. After much wrangling in Congress, he signed the Federal-Aid Highway Act of 1956 into law, heralding the beginning of the IHS. The Act also instituted size and weight limits for vehicles using federally funded highways and instituted a matching funds system (90% federal to 10% state) for interstate construction. Recognizing that vehicle weights impacted road per- formance, size and weight limits were incorporated to safeguard the federal government’s share of those funds (Al-Qadi et al., 2016). The Bureau of Public Roads worked with the American Association of State Highway Officials (AASHO) to develop minimum standards for construction that would ensure uni- formity of design, full control of access, and elimination of highway and railroad-highway grade crossings. Those minimum standards were largely developed from the AASHO Road Test (FHWA, 2017). The AASHO Road Test was a full-scale experiment that studied flexible pavement, rigid pavement, short-span bridges with steel beams, and short-span bridges with concrete beams

Introduction 7 trafficked with trucks carrying known loads at established weights. The experiment consisted of 7 miles of two-lane pavements constructed in six two-lane loops with 836 test sections. The cost was $27 million in 1960 dollars, which is approximately $250 million in 2019 dollars. Construction began in August 1956. Test traffic started on October 15, 1958, and terminated on November 30, 1960. The goals included monitoring change in performance versus axle loads and developing design relationships to use for pavement design. Variables studied included materials, thicknesses, surfaces, bases, subbases, and soils, all to the extent available in Ottawa, Illinois (Highway Research Board, 1962). This experiment on full-scale test roads with known-weight trucks made the connections among axle loads, axle load accumulation, and performance. It also originated the concept of the 18,000 lb. ESAL, which became the standard measure of vehicle axle weight by which to gauge performance and damage to pavement and bridge structures. The AASHO Road Test resulted in design standards based on the performance of pavements and bridges according to known accumulations of axle weights. In the experiment, researchers knew the weight of trucks and the number of passes on the test sections. The problem was that any vehicle could use a public road, and its weight was unknown to the roadway owner. Hence, there was a need to know the weight of vehicles using the road system in order to design the pavement for the traffic that would use the road. Early WIM An early effort to collect truck weights in motion actually pre-dated the AASHO Road Test. In 1951, Norman and Hopkins at the Bureau of Public Roads used a concrete plat- form embedded in the roadway and supported by strain-gauge load cells to measure vehicle weights. As a vehicle passed over the platform, they captured data by photographing oscilloscope traces (Al-Qadi et al., 2016). In 1956, Clyde Lee, a master’s student at Mississippi State College, wrote his master’s thesis, entitled “A Portable Electronic Scale for Weighing Vehicles in Motion,” where he described a portable device that could weigh vehicles in motion. He built a weighing plate consisting of strain-gauge load cells sandwiched between steel plates, an amplifier system, and a recording device. He first used an oscilloscope for displaying the sensor output, and then for a permanent record used a strip chart recorder. Calibrating the system with vehicles of known weight, he developed a scale on the strip chart recorder paper to display vehicle weight as a vehicle traveled across the sensor. The thesis recognized that the scale system needed many improvements, but it provided a proof of concept for WIM (Lee, 1956). Dr. Lee’s pioneering work continued as he joined the University of Texas as an assistant professor in 1959 and in 1966 received Patent Number 3,266,584 for “Vehicle Weighing Scale with Overlapped Load Bearing Plates” (Lee, 1966). Dr. Lee contributed more to the advance- ment of WIM throughout the years with additional research. In a 1985 paper documenting WIM research for the Texas State Department of Highways and Public Transportation (now the Texas Department of Transportation), Dr. Lee and his research team tested a WIM system developed by the Radian Corporation and compared the results to static weights for 800 trucks. One notable conclusion was that WIM systems required on-site calibration to give reliable data (Lee et al., 1985). Modern WIM To expand the use of WIM systems, certain problems had to be addressed, including sensor durability, accuracy and calibration, and data collection and evaluation.

8 Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications Standardization Standardization was key to the future development of WIM. Dr. Lee led the effort to develop the first ASTM standard for WIM, ASTM E-1318, “Standard Specification for Highway Weigh- in-Motion (WIM) Systems with User Requirements and Test Methods” in 1990 (International Society for Weigh in Motion, 2012). Technology Technological improvements since the 1950s and particularly since the 2000s have addressed many of the identified needs. Improvements in electronics provided better sensors and elec- tronic data collection, electronic data storage devices, computers to analyze data, and high- speed Internet and wireless communications to transmit data to remote locations. These improvements across time have helped to facilitate the evolution of WIM to its current state of the art. In addition, advancements in technology to measure pavement smoothness helped to determine the level of smoothness needed in the pavement upstream and downstream of installed WIM sensors. LTPP and Its Effect on WIM The Long-Term Pavement Performance (LTPP) program began as part of the 5-year national Strategic Highway Research Program (SHRP) in 1987. The goal was to follow the performance of test sections to the end of their design life in order to add to the knowl- edge of pavement performance. LTPP activities began in 1989 and identified 2,509 test sections for performance monitoring. More sections were added as new materials, tech- nologies, and work methods were developed subsequent to the selection of the original test sections. When the SHRP program ended, FHWA took over management and continues the project today. Part of the LTPP program involved using WIM to monitor traffic on test sections. LTPP research managers originally wanted WIM sites for every test section, but soon realized that the cost was prohibitive. However, LTPP staff selected a subset of test sections for WIM moni- toring. In most cases, state DOTs were responsible for installing the systems and collecting the WIM data. In 1996, an LTPP program assessment revealed major problems with WIM data, noting issues with accuracy, calibration, and missing data. Because monitoring performance relies on knowing how traffic degrades performance, WIM data were a key component in the success of the program. This assessment triggered an action plan to improve WIM data collection. LTPP performed studies to address equipment, calibration, installation, and smoothness of pavements to obtain what LTPP defined as “research-quality data.” LTPP developed and implemented protocols to bring the quality of WIM data up to the level needed to monitor pavement performance. By 2003, the program had sufficient protocols and equipment in place to collect reliable research-quality data, leading to verification of the ASTM E-1318 standard, development of the new AASHTO M 331-17, “Standard Specification for Smoothness of Pavement in Weigh-in-Motion (WIM) Systems,” and a field protocol for WIM system calibration and validation. LTPP-led studies also resulted in an LTPP vehicle classification table and default inputs for the AASHTO Mechanistic-Empirical Pavement Design Guide and AASHTOWare Pavement ME Design software (discussed later) (FHWA, 2015; Transportation Research Board, 2017). These protocols formed the basis for the modern WIM industry to grow.

Introduction 9 Report Organization This remainder of this report is organized as follows: Chapter 2. Literature Review. This chapter summarizes the literature review conducted to identify uses of WIM in pavement design, bridge design, and asset management and load rating; commercial vehicle weight enforcement support; and freight planning and logistics. Chapter 3. State of the Practice. This chapter describes the state-of-the-practice agency survey, the agencies that responded, and the information that was developed from the surveys. A copy of the survey is found in Appendix A, consolidated survey responses are found in Appendix B, and data on WIM system types, by agency, are found in Appendix C. Chapter 4. Case Examples. This chapter documents the case examples, relaying informa- tion obtained from interviews of five selected survey respondents representing their DOT. These examples provide more detail than survey results can, describing the five DOTs’ use of WIM, the problems these DOTs face in this area, and experiences or thoughts for the future of WIM. Representatives from the California, Minnesota, Florida, Maryland, and Tennessee DOTs were interviewed for these case examples. A summary of each inter- view and findings from interviews as a whole are presented. Chapter 5. Conclusions and Further Research. This chapter summarizes the synthesis, documents impediments to using WIM, and describes knowledge gaps as well as research that could address those gaps.