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

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15 This synthesis included developing a survey 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, the type of staff who use WIM data, and impediments to the use of WIM data. A copy of the survey is found in Appendix A. Consoli- dated survey responses, by agency, are found in Appendix B. Background The survey request was sent to all 50 state DOTs in the United States, 6 Canadian provincial DOTs, and NYCDOT. When the survey response period ended, 45 U.S. state DOTs, NYCDOT, and 6 Canadian provincial DOTs had completed the survey. The U.S. state DOT response rate was 90%, with 45 of the 50 DOTs responding. The response rate from all 57 DOTs that sent the survey was 91.2%. In some cases more than one person responded from a DOT because sometimes responses were a team effort, with various staff members contributing expertise about different compo- nents of the DOT operation and use of WIM data. These responses were consolidated to produce one agency response for use in this study’s analysis. Some questions were designed as “select all that apply,” and consequently totaled responses to a question can add up to more than 100%. In these cases, it may be more meaningful to study the number of responses rather than a percentage. The title of respondents included Engineer (pavement, bridge, design, traffic management, weight enforcement, other), Transportation Planner, Data Collector, Data Monitor, Data Manager, Data Analyst, and Technician. This shows a wide variety of agency personnel either collecting or using WIM data. The U.S. state and Canadian Province DOTs that responded to this survey are shown in Figure 1. Summary of Survey Responses This section provides a summary of the various survey question responses. Current Status Of the 52 agencies that completed the survey, 87% responded that the agency is currently collecting WIM data, as shown in Figure 2. C H A P T E R 3 State of the Practice

Figure 1. U.S. states (orange) and Canada provinces (blue) that responded to the survey.

State of the Practice 17 Five agencies used to collect WIM data, but do not now. These agencies answered all other questions based on what the agency did when they were collecting WIM data. One of these DOTs did indicate that they are planning to redevelop a WIM program for enforcement and planning activities. Two agencies indicated that they have never collected WIM data. Types of WIM Systems As shown in Figure 3, out of the 50 agencies that are collecting or have collected WIM data, 70% have quartz piezo-electric WIM systems, followed by 30% with bending plate WIM systems. Most agencies have more than one type of system, as seen by the percentages adding to more than 100%. A few agencies have three or more types of WIM systems. A detailed list of each agency and the systems they use can be found in Appendix C. WIM Data State DOTs and other agencies mainly use their WIM systems to determine axle and gross vehicle weight and for vehicle classification. Figure 4 shows the data use response by WIM system type. This response could show that a particular sensor type was seen as better for certain data collection. The sensor types have no significant differences of use. 2 (4%) 5 (10%) 45 (87%) 0 10 20 30 40 50 No - the agency has never collected WIM data The agency used to, but not now Yes Number of Agencies n=52 Does your agency collect WIM data? Figure 2. Current WIM data collection status. 10 (20%) 9 (18%) 14 (28%) 15 (30%) 35 (70%) 0 5 10 15 20 25 30 35 40 Other WIM system Load cell WIM system Polymer/Ceramic piezo-electric WIM system Bending plate WIM system Quartz piezo-electric WIM system Number of Agencies n=50 What WIM systems does your agency have? Figure 3. WIM systems used by different agencies.

18 Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications Although some agencies use their WIM systems for purposes “other” than the four offered in the question (i.e., determine axle and gross vehicle weight, vehicle classification, and axle load spectrum), most of them did not indicate what those usages are. Those agencies that did indicate alternative usages specified the following applications of WIM data: • Enforcement: Axle and weight violations • Axle spacing • Vehicle spot speed and traffic volume • Screening at weigh stations or port of entry • Participation in LTPP program • Sorting trucks at weigh stations • Checking for unbalanced loads • Using truck profiles for bridge design Calibration Most agencies calibrate their WIM systems when they are installed and then annually as shown in Figure 5. Sixteen percent of the agencies calibrate WIM systems semiannually or more often. Thirty percent of the agencies recalibrate their systems when validation fails. According to the response of agencies that selected other frequencies of calibration, they calibrate WIM systems according to these schedules: • When needed (some agencies provided information regarding how they determine when a calibration is needed, while some agencies did not) • Every 2 to 5 years, depending on the agency • Autocalibration Appendix B provides more details about how often each agency calibrates their WIM systems. Quality Control of WIM Data The majority of agencies perform quality control on data collected by WIM systems, as shown in Figure 6. 0 5 10 15 20 25 30 35 40 Bending plate Quartz piezo- electric Polymer/Ceramic piezo-electric Load cell Other WIM system N u m b er o f A g en ci es ( n =5 0) How does your agency use the data from WIM systems? Determine axle weights Vehicle Classification Axle Load Spectrum Gross Vehicle Weight Other Figure 4. Usage of the data from WIM systems.

State of the Practice 19 Five state DOTs do not perform quality control. This may be because they have not had issues with quality control of the data, possibly due to their calibration and maintenance procedures eliminating most data issues. All but six state DOTs answered the question about how they address quality control issues. As indicated in Figure 7, 76% of the agencies flag the problematic data and review them for inclusion or exclusion. About 30% of agencies choose to directly remove the problematic data. Some agencies chose more than one answer, resulting in a more than 100% agency response. This indicates they handle quality control in multiple ways. Other methods agencies use to address WIM data quality control issues include the following: • Conducting on-site observations to check for hardware or pavement condition problems. • Investigating for possible recalibration. • Discontinuing use of suspected “bad WIM data” in end-use applications until the reason for bad data is corrected. Problems with WIM Data The significant problems agencies have with WIM data are shown in Figure 8. Many DOTs indicated they have more than one problem. Nearly 80% of agencies reported that they have 1 (2%) 8 (16%) 15 (30%) 16 (32%) 23 (46%) 27 (54%) 0 5 10 15 20 25 30 Didn’t answer Semiannually or more often When Validation Fails Other Annually When Installed Number of Agencies n=50 How often do you calibrate your WIM systems? Figure 5. Calibration frequency. 1 (2%) 5 (10%) 44 (88%) 0 5 10 15 20 25 30 35 40 45 50 Didn’t answer No Yes Number of Agencies n=50 Does your agency perform Quality Control on all incoming data? Figure 6. Number of agencies that perform WIM data quality control.

20 Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications 6 (12%) 5 (10%) 14 (28%) 38 (76%) 0 5 10 15 20 25 30 35 40 Didn’t answer Other (text input) Data are removed Data are flagged and reviewed for inclusion or exclusion Number of Agencies n=50 How are any Quality Control issues addressed? Figure 7. How agencies address quality control issues. 2 (4%) 3 (6%) 9 (18%) 10 (20%) 11 (22%) 14 (28%) 20 (40%) 21 (42%) 31 (62%) 39 (78%) 0 5 10 15 20 25 30 35 40 45 Problems with storing data None Other (text input) Problems with classification of traffic Outliers Problems with transmission of data Problems with loops Missing data WIM goes out of calibration Problems with sensors Number of Agencies n=50 What are any significant problems you have with WIM data? Figure 8. Significant problems with WIM data. some problems with sensors. More than 60% of agencies indicated that they have problems with WIM going out of calibration. Missing data and problem with loops are also identified as major problems with WIM data by about 40% of the agencies. Only three agencies said they do not have any significant problems with WIM data. In the category of “Other,” a significant response was that weather or roadway conditions cause WIM calibration and data problems. Data Sharing The agencies were asked if they report or share WIM data with any in-agency or out-of-agency entities. The results are shown in Figure 9. The purpose of this question is to better understand how WIM data are used within or outside of DOTs. All agencies responding to the survey share data with at least one other entity. Of the 45 U.S. DOTs responding to this survey, 39 indicate they send their WIM data to FHWA.

State of the Practice 21 Supporting pavement design is a major usage of WIM data as 76% of the agencies share WIM data with in-agency pavement designers. WIM data are also often shared with in-agency bridge designers, asset management groups, and freight planning groups. More than half of the agencies share their data with universities. Those agencies who provided a write-in answer in the “Others” box mentioned sharing data with other state agencies, law enforcement, and legislative bodies. WIM data are readily available on request in most agencies. Use of WIM data The survey then asked specific questions about how agencies use WIM data for pavement design, bridge applications, asset management or load ratings, and freight planning or logistics. Pavement Design Figure 10 charts the responses to the question of whether the agency used WIM data for pavement design. It was a multiple-choice question where an agency chose all that applied; con- sequently the percentages add to more than 100%. Many agencies are providing more than one type of information to pavement designers. More than 60% of agencies use WIM to assist in average daily traffic (ADT) counts for pavement design. Half of the agencies use WIM data to calculate ESALs, the average ten heaviest wheel loads daily (ATHWLD), or percentage of tandem axles for use in pavement design or load zone roadway analysis. Nearly 40% of them also use axle load spectrum obtained from WIM data or provide pavement designers with a traffic analysis report to support pavement design. While many states use WIM data in multiple ways to aid in pavement design (as evidenced by total percentage adding to greater than 100%), 19 states use WIM to support an ME pavement design system. “Other” text inputs to this question indicate that some agencies used WIM data to determine averages for pavement design and use this for standard pavement designs. 2 (4%) 5 (10%) 5 (10%) 5 (10%) 6 (12%) 6 (12%) 12 (24%) 16 (32%) 19 (38%) 20 (40%) 21 (42%) 23 (46%) 27 (54%) 38 (76%) 39 (78%) 0 5 10 15 20 25 30 35 40 45 Cities Toll Authorities MPO or COG Counties Post on-line for download by anyone Other DOTs Others (Fill in box) In-Agency asset management group In-Agency bridge designers In-Agency freight planning group Consultants Law enforcement Universities In-Agency pavement designers FHWA Number of Agencies n=50 Do you report/share WIM data with in-agency or out-of-agency entities? Figure 9. WIM data sharing.

22 Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications 3 (6%) 4 (8%) 7 (14%) 19 (38%) 20 (40%) 25 (50%) 33 (66%) 0 5 10 15 20 25 30 35 No Didn’t answer Other (Fill in box) Axle Load Spectrum used in an AASHTO Pavement ME or similar pavement design procedure. Provide pavement designers with a traffic analysis report, for pavement design purposes based on WIM data. Calculate ESALs, or Average of Ten Heaviest Wheel Loads (ATHWLD) or percent tandem axles for use in pavement design or load zone roadway analysis. Use WIM to assist in ADT (vehicle counts, truck splits, and directional distribution) for pavement design. Number of Agencies n=50 Do you use WIM data in pavement design? Figure 10. How agencies use WIM in pavement designs. Bridge Applications While WIM data are often used to support pavement design, not many agencies currently use WIM for bridge applications, as Figure 11 indicates. Some agencies use WIM for more than one bridge application (as seen by the total adding to more than 100%). Seventeen agencies indi- cated they do not use WIM for any bridge design application, and another seven agencies did not respond to the question. The majority of those agencies that did use WIM data in bridge applications mainly provide ADT-related information to support bridge designs. “Other” usages of WIM data to support bridge applications include determining load factors for load rating in research, identifying overweight trucks, developing truck profiles, and evaluating loads on bridges. Asset Management or Load Ratings Nearly half of the agencies do not use WIM data for any asset management or load rating purposes, as indicated in Figure 12. Nearly 40% of the agencies use WIM data for pavement management. Less than 20% use WIM data for pavement load ratings, bridge load ratings, or bridge management. Only one DOT uses WIM data for evaluating bridge remaining life. Freight Planning or Logistics Nineteen agencies responded in the survey that they do not use WIM data in freight planning or logistics, as shown in Figure 13. Twenty-one agencies use WIM data to help evaluate freight movements. Eleven agencies use WIM data for corridor planning and only a few agencies use them for facility design. The text inputs from respondents to this question indicate that WIM data are used mainly to support freight planning related to heavy or overweight commercial vehicles. One agency uses WIM data to support their freight policy development, which regulates truck weight compliance and permitting. Another DOT is not currently collecting WIM data, but they did plan to use WIM data for freight planning in the future implementation of their WIM program.

State of the Practice 23 4 (8%) 4 (8%) 5 (10%) 5 (10%) 6 (12%) 7 (14%) 17 (34%) 19 (38%) 0 2 4 6 8 10 12 14 16 18 20 Bridge load ratings (LRFR or other procedure) Other bridge design procedure (using WIM data) Percent trucks running side by side LRFD design procedure (using WIM for local load factor calibration) Other (Fill in box) Didn’t answer No Use WIM to assist in ADT (vehicle counts, truck splits, and directional distribution) for a bridge design method Number of Agencies n=50 Do you use WIM data in bridge applications? Figure 11. How agencies use WIM data in bridge applications. 1 (2%) 5 (10%) 6 (12%) 7 (14%) 9 (18%) 19 (38%) 22 (44%) 0 5 10 15 20 25 Bridge Remaining Life Didn’t Answer Bridge Load Ratings Bridge Management Pavement Load Ratings Pavement Management None Number of Agencies n=50 Do you use WIM data in asset management or load ratings? Figure 12. How agencies use WIM data in asset management or load ratings. Law Enforcement Law enforcement is another major usage of WIM data. This is consistent with agency responses to a previous question asking how agencies use their WIM data. Quite a few agencies mentioned using WIM data for law enforcement purposes. A majority of the agencies responded that they do not have law enforcement or weight enforcement responsibilities (as shown in Figure 14), but they do use WIM data to support weight enforcement by, for example, sharing data with law enforcement agencies, as Figure 15 indicates.

24 Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications 4 (8%) 4 (8%) 5 (10%) 11 (22%) 19 (38%) 21 (42%) 0 5 10 15 20 25 Didn’t answer Facility design (entrance/exit design, complete streets, border crossings) Other (Fill in box) Corridor planning None Freight movements Number of Agencies n=50 Do you use WIM data in freight planning or logistics? Figure 13. How agencies use WIM data in freight planning or logistics. 1 (2%) 36(72%) 13 (26%) 1 (2%) 27(54%) 22 (44%) 0 5 10 15 20 25 30 35 40 Didn’t answer No Yes Number of Agencies n=50 Does your agency have law or weight enforcement responsibilities? Weight enforcement Law enforcement Figure 14. Number of agencies with or without law or weight enforcement responsibilities. 2 (4%) 17(34%) 31 (62%) 0 5 10 15 20 25 30 35 Didn’t answer No Yes Number of Agencies n=50 Do you use WIM data to support weight enforcement? Figure 15. Number of agencies using WIM data to support weight enforcement.

State of the Practice 25 Reasons for Not Using WIM for Some Applications As indicated in Figures 10 through 13, many agencies do not use WIM data for one or more of the applications (e.g., pavement design, bridge design, asset management, load rating, freight planning) cited in those questions. Their reasons are shown in Figure 16. The top reason given is lack of budget. Other major reasons include an insufficient number of WIM stations to provide effective data, poor data quality, no present need, and lack of knowledgeable and trained personnel. Some agencies provided text input to this question describing their issues with using WIM data for some of those applications. Their reasons include a lack of funding for maintenance and 1 (2%) 1 (2%) 1 (2%) 1 (2%) 2 (4%) 3 (6%) 3 (6%) 4 (8%) 4 (8%) 5 (10%) 6 (12%) 8 (16%) 10 (20%) 11 (22%) 12 (24%) 14 (28%) 15 (30%) 18 (36%) 0 2 4 6 8 10 12 14 16 18 20 Didn't answer Traffic conditions do not require WIM (low traffic, few trucks) Difficulty calculating the initial cost of purchase and installation and the long-term calibration and maintenance costs of WIM equipment Lack of guidance regarding locating WIM systems on the network to maximize value of data Lack of guidance regarding equipment selection for the application Data collected by another agency Difficulty developing an implementation plan for installing and using WIM systems and data on the network – which locations should be instrumented first, second, third….etc Lack of agency authority Need proper installation guidance methods to ensure best data quality Lack of guidance regarding the number of WIM systems needed considering network size, route types, traffic data mix and statewide application of WIM data Do not use design/asset management procedures that require WIM data Lack of knowledgeable and trained personnel (DOT or Law Enforcement) No present need Poor data quality Other (Fill in box) Lack of (a sufficient number of) WIM stations to provide effective data N/A Lack of budget Number of Agencies n=50 Are there reasons that you do not use WIM data for any one or more of the above applications? Figure 16. Reasons for not using WIM data for those applications discussed in the survey.

26 Use of Weigh-in-Motion Data for Pavement, Bridge, Weight Enforcement, and Freight Logistics Applications calibration, issues with the durability of sensors, technical issues with handling the data, insufficient data quality for some applications, and legal challenges. Other WIM Data Uses When asked if the DOT has found different uses of WIM data other than those described in the survey, 82% of them indicate “No” and 16% said “Yes,” as shown in Figure 17. Other usages of WIM data mentioned by different agencies can be summarized as: • Freight taxonomy: Identify the type of commodities carried by truck • Determination of truck load level (full, empty, partially filled, cubed out) • Assistance for law enforcement • Support of university research • Smart infrastructure (“Nanowim,” which uses a concrete additive that makes concrete electrically responsive to loading and can be used as a WIM sensor) • Electronic screening at ports of entry. Survey Summary Taken as a whole, the survey provides a good snapshot of the state of the practice for WIM in the United States and Canada. Below are summary statements about the survey data. • Most (96%) agencies collect or have collected WIM data. • Agencies have a wide range of equipment types and many have periodic problems with equip- ment (sensors and data quality). • WIM systems are costly and some agencies see funding for installing and maintaining these systems as a constraint to using WIM data within the DOT. Funding for installation is easier to justify, but the continued funding for maintenance and calibration was harder to justify in the annual budget. • Many agencies use WIM data to aid in pavement design, although most are not currently using a Pavement ME Design application. • WIM systems for bridge design and asset management purposes are used by a much smaller number of DOTs. • Agencies willingly share their data within their organization and with others that request the data. • One impediment to sharing data is that people who might use the data either do not know the data exist or they do not see a benefit from using the data. 1 (2%) 8 (16%) 41 (82%) 0 10 20 30 40 50 Didn’t answer Yes No Number of Agencies n=50 Have you found different uses for WIM data other than those described in this survey? Figure 17. Agencies’ responses about different uses of WIM data.