Minnesota Department of Transportation

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MnROAD | NRRA | Structure & Teams | ICT Team

Effective Use of Traffic Speed Deflectometer for Network-based and Project-based Applications

Status: In development


To fully characterize the overall condition of pavements in the highway network and assess their maintenance and rehabilitation (M&R) needs, State Highway Agencies (SHAs) must employ practical data collection methods to evaluate the pavement surface condition as well as the pavement structural condition. The consensus is that incorporating the structural condition along with the surface condition into the pavement management decision-making processes can lead to better-informed and more cost-effective decisions. The limitations of the existing devices such as the Falling Weight Deflectometer (FWD), the device of choice for the backcalculation of layer properties and mechanical evaluation, and the desire to characterize the network-level structural condition have led to research efforts to investigate, validate, and demonstrate the effectiveness of Traffic Speed Deflectometer Devices (TSDs) in recent years. TSDs offer the advantage of improved operation safety, circumventing the need for temporary traffic control and lane closures, and increased spatial coverage over the stationary FWD.

This project focuses on developing analysis methodologies and guidelines for the classification of pavement sections using Traffic Speed Deflectometer (TSD) technology based on structural soundness categories and structural-based indices, and to evaluate the feasibility of TSD for project-based applications including backcalculation of modulus and calculation of the structural number (SN). The study aims to identify those indices meaningful for network and project-level applications and develop guidelines to identify those best suited based on the type of pavement. Several algorithms exist to provide the network-level and project-level information mentioned. However, none of them have considered the uncertainty of the data collected measurements related to the type and stiffness of the pavement type, and related to the TSD hardware and software.

The results of this study will be of particular value to SHAs to maximize their benefit-cost-ratio of using TSD by avoiding data collection on sections that are outside the useful range of operation of TSD and use the best algorithm to analyze the data collected that balances the uncertainties in the measurements and analysis.

The objective of this study is to provide solid guidelines and processes to SHAs on the best use of TSD to maximize the information extracted for their network- and project-level uses and minimize the cost of data collection.

Project Tasks

Task 1: Technical Advisory Panel (TAP) management

This task will form and manage the TAP that will advise NRRA and the project team on the conduct of this study. Coordinate and conduct a virtual kick-off meeting with the TAP within 30 days of contract execution to discuss project scope and tasks. Additional virtual meetings with the TAP and the research team will be held at the project mid-point and near the end of the project to report progress and request feedback.

  • Deliverables: One kick-off meeting minutes. Oral reports and presentations on the progress and results of this project will be provided to NRRA.

Task 2: Document state of knowledge and initial memorandum of expected research benefits and potential implementation steps

This task will document the state of knowledge and the state of practice and the latest advancement in the area of TSD for network-level and project-level applications. Alternative analysis approaches advocated by different institutions will be reported with their preliminary strengths and weaknesses. Case studies will be documented along with an initial assessment of research benefits.

  • Deliverables: Technical memorandum documenting the state of knowledge, historical case studies, initial estimates of expected research benefits, and documentation of the methodologies

Task 3: Gap analysis of TSD adoption and preliminary evaluation of existing data

To delineate strengths, application opportunities, and existing gaps regarding TSD integration to network-level operations, the research team will carry out a comprehensive gap and SWOT (strengths, weaknesses, opportunities, and threats) analyses considering data components that complement TSD data to carry out a complete structural evaluation, parameters needed in decision trees for treatment selection, and data quality control during TSD data collection and post-processing.

In addition, a preliminary assessment of TSD application toward network-level operations will be conducted using data collected under NCHRP Project 10-105 in 2021, and existing data obtained from Transportation Pooled Fund TPF-5(385) after coordination with MnDOT to procure this data. The research team with the assistance of NRRA DOTs will also compile the respective pavement surface condition information in the form of condition scores, and distress ratings, along with other pavement type descriptors and FWD data. The furnished data will undergo preliminary data analysis to assess data reduction and data processing, deflection indices, and deterioration trends using descriptive statistics. Existing thresholds of deflection indices (as provided in the literature) will be evaluated for the categorization of structural soundness and propose a framework to categorize pavement structural soundness using TSD data while considering the pavement type and deterioration level.

Concurrently, the research team will also evaluate existing TSD data to assess the potential of TSD technology to be utilized for project-level applications. The analysis will consist of a preliminary assessment of how TSD measurements—i.e., TSD deflections and/or deflection-based indices along with existing models—can be used considering the different pavement structural categories to characterize the pavement structure, establish thresholds, and estimate the in-situ layer moduli via backcalculation. Correlations and trend analyses will be conducted to identify those pavement structures or conditions that may lend themselves as being more suitable for project-level applications with TSD, as well as to identify possible causes or sources of deviation

  • Deliverables: A memorandum containing a gap analysis of available data and current procedures to incorporate TSD information in the classification of pavement structural soundness, as well as the necessary components to perform project-level analysis for design and forensic purposes. Field case studies describing sites condition and reduced measurements from TSD and preliminary results including descriptive statistics of case studies with TSD collected data and other relevant test devices supplementing the experimental tests such as FWD deflection bowls, TSD speed, GPR-identified layer thicknesses, delamination, or distress.

Task 4: Develop a plan for field studies and draft initial guidelines for TSD adoption

After evaluating the limitations on the use of the technology, reliability of the measurements, equipment and processing requirements, and data processing and interpretation requirements based on case studies previously documented, the research team will develop a plan that will include data collection protocols that will support the field studies. This plan will be prepared and shared with the TAP to obtain feedback and accommodate modifications that best suit NRRA’s operations and testing plans. The data collection recommendations will serve the purpose of obtaining TSD data and supplementary test data for validating the network-level and project-level methodologies in Task 4. The proposed data collection plan will be based on the gap analysis and the preliminary analysis results obtained from Task 1. Considering that MnDOT and other NRAA members may have collected TSD data in FY 2023 before the start of this project, this data collection plan may be implemented as part of a coordinated effort for routine TSD testing to be carried out as a part of TPF-5(385) pooled fund study for FY 2024. The plan will inform NRRA members of the data necessary from field test cases that will serve as supporting data for TSD calibration and validation of the products of the following tasks. Data may include condition and distress ratings, functional information, material properties, and pavement structure, among other information collected from additional testing such as the FWD. The research team considers that distinct pavement structures (both flexible and rigid) with different geomaterials should be considered to assess the effectiveness of TSD toward network and project-level applications. If the TAP deems it beneficial, the research team may instrument a test section to evaluate the accuracy of the TSD measurements. Using the preliminary analysis of data obtained from previous case studies, draft guidelines for instituting TSD for PMS operations will be proposed. The guidelines will address the following items:

  • A detailed methodology and step-by-step guidance on how to incorporate TSD to identify/classify structural soundness categories at a network level.
  • Proposed analysis methods of TSD information and selection of candidate deflection indices, recalibrated SN, and identification of “soft spots.”

  • Deliverable: A memorandum containing a plan with recommendations for data collection protocols that will support MnDOT data collection procedures and draft guidelines for instituting TSD for PMS operations

Task 5: Analyze Field-Collected Data to Develop Guidelines to Integrate TSD into Network-Level Operations and Project-Level Applications

Analyze collected data to develop guidelines and recommendations toward establishing deflection basin indices thresholds, identify functional conditions, and soft spot identification for network-level procedures. This task will also verify how TSD measurements correlate with the FWD and evaluate existing models to predict the structural condition (SN), backcalculated moduli, and structural and functional performance of the pavement sections. To ensure the appropriateness and practicality of the proposed guidelines for use for both networkand project-level applications, the research team will proceed with the analysis of TSD data collected by MnDOT as part of the TPF-5(385) pool fund study. If deemed necessary, in consultation with TAP, data collected by other SHAs as part of the pooled fund can be incorporated to supplement the collected information, providing additional material corresponding to roads with structural and functional conditions different from those at Minnesota test sites. The research team will make use of FWD, GPR, and other relevant testing collected by MnDOT to verify that the TSD measurements correlate with the FWD, the suitability of TSD measurements given their uncertainty and variability for the type of pavement and condition, and that the developed models and/or procedures predict the structural condition (SN), backcalculated moduli, the structural and functional performance of the pavement sections. Using the data collected, the research team will aim to refine the proposed methods and analysis procedures. This process will be carried out through rigorous statistical and reliability approaches for defining the risks and benefits of the different methods proposed, as well as their limitations. The research team considers the focus of this project should be on the development of the methodologies and fine-tuning of the proposed relationships, as well as recommendations for the integration of the TSD data into the PMS. As such, a list of recommendations will be developed to implement and/or supplement the proposed methodologies. An assessment of the feasibility of using TSD for project-level applications will also be documented.

  • Deliverable: Memorandum with preliminary draft guidelines for adoption of network-level operations and project-level applications. Analysis results of the field studies including validation of models, evaluation of deflection-based indices, evaluation of thresholds, and any additional correlation with other relevant test devices supplementing the experimental tests such as FWD deflection bowls, will be documented.

Task 6: Refine proposed TSD guidelines

Following the analysis and findings of the data collected in the field case studies and the amendment and/or refinement of the methods proposed, the research team will draft revised guidelines for the use of TSD. Guidelines will be developed for using TSD for network-level applications, which will include:

  • Detailed methodology and step-by-step guidance on how to incorporate TSD to identify structural conditions using representative indices and to classify pavement into an appropriate structural soundness category at a network level, e.g. using deflection basin indices thresholds. This method shall also include the integration of pavement surface conditions and functional performance parameters.
  • Methodology to extract TSD information (e.g., structural adequacy, moduli) for PMS integration.

Guidelines will be developed for using TSD for project-level applications for types of pavements identified as promising for implementation. The drafted guidelines will provide:

  • Detailed step-by-step method to backcalculate in situ layer modulus using deflection-basin indices.
  • Methodologies for calculating structural condition index and effective structural number.

Feedback on the practicality of the proposed guidelines for TSD integration to network-level operations, their integration into the PMS for M&R decisions, and project-level applications, will be vital to the success of this project. For this purpose, a roundtable will be facilitated for the research team to obtain feedback from the TAP about the developed guidelines. The research team considers Office of Maintenance staff and District personnel would benefit from the discussion and may be invited to attend upon TAPs consideration. The roundtable will be made through a webinar to accommodate more personnel and encourage more contributions. The research team will open the discussion with a brief overview of the scope of the project and will continue with an overview of the guidelines with the proposed framework to use TSD data useful for network-level applications.

Feedback obtained from attendees will be documented to ensure that the guidelines will be of benefit to the end-users. At this stage, the guidelines will also be modified to address as many of the concerns as possible. A technical memorandum will be developed documenting the issues to refine the guidelines and processes.

  • Deliverable: A technical memorandum with the refined proposed guidelines for TSD integration for network-level operations, and project-level applications, as well as recommendations for integration to PMS.

Task 7: Final Report

A draft project report summarizing the results, findings, conclusions, and recommendations of the research will be delivered. The report will comply with MnDOT’s Editorial guidelines. The report will include an implementation plan for improving and deploying the products of the research and a draft specification in AASHTO format. Upon the feedback of the TAP, the final report will be finalized for delivery.

  • Deliverable: A final report that is finalized based on the TAP review, and a revised report that is technically complete and approved by the TL for publication.

Project team

Email the Project Team
Principal Investigator: Soheil Nazarian, UTEP, nazarian@utep.edu
Technical Liaison: Eyoab Zegeye, MnDOT, eyoab.zegeye@state.mn.us
Project Technical Advisory Panel (TAP): Contact us to join this TAP

  • Tim Anderson, MnDOT
  • Emil Bautista, MnDOT
  • Tom Burnham, MnDOT
  • Shongtao Dai, MnDOT
  • Steve Henrichs, MnDOT
  • Micah Holzbauer, MnDOT
  • Mike Lanotte, Michigan State University
  • Joseph Podolsky, MnDOT
  • Marcos Sanchez-Pliego, MnDOT
  • Nicholas Schaefer, Surface Systems and Instruments
  • Nadarajah "Siva" Sivaneswaren, FHWA
  • Dave Van Deusen, MnDOT
  • Eyoab Zegeye, MnDOT (TL)

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