In recent decades, significant progress has been made in the development of Traffic Speed Deflection Devices (TSDDs), with more than 20 TSDDs currently in use worldwide. However, there are no commonly accepted rules and procedures for calibration and approval of these systems. Established approaches for stationary bearing capacity measuring devices, such as the falling weight deflectometer (FWD), cannot be directly used for TSDD applications, but form a good basis to start from. NCHRP Project 10-105 investigated using FWD data to verify TSDD measurements and demonstrated that many factors in the field could significantly impact the confidence of the proposed FWD-based verification approach. As more and more state agencies collect TSDD data, they plan on incorporating it into their pavement management process at network and project levels. However, unexplained TSDD measurement variations could misguide the decision-making process, leading to inappropriate maintenance and rehabilitation decisions. Pavement managers need a good verification tool to perform quality assurance of the TSDD systems and develop confidence in the quality of TSDD data for pavement management and design decision-making.
Due to the dynamic measurement nature of the TSDD, checking the calibration and thus the approval of the measuring systems is only possible in moving operation. Setting up stationary calibration facilities, as is the case in FWD calibration centers, is therefore not possible. Innovative approaches must be found that make it possible to produce reproducible and comparable calibration sections. In addition, suitable section lengths must be determined, and the scope and documentation of self-monitoring by the operator must be defined. All approaches are to be derived independently of the device and applicable to all TSDDs.
The objective of the proposed research is to develop a reliable procedure to ensure the quality of pavement structural assessments with TSDD devices. The procedure should be adapted to the special requirements and challenges of TSDD measurement technology and be reproducible at different locations. The desired research is expected to improve asset performance; strengthen resiliency; assist in evaluating emerging trends in technologies, policies, and practices; and innovate and modernize products and services. To achieve this objective, the research will review literature, develop a catalogue of requirements, make material investigations on laboratory scale and small scale (e.g., stiffnesses, durability, temperature sensitivity), perform conceptual designs of a demonstrator, construct a demonstrator, potentially convert into a calibration center, collect/analyze TSDD measurements and measurements with comparison systems, and design a calibration and construction specification. The research should include several tasks: (1) conduct a literature review to identify existing calibration methods and their pros and cons and document the reasons why existing methods do not work and summarize the critical calibration requirements/needs; (2) identify or develop methodologies for effectively calibrating the TSDD devices (identify critical calibration requirements; develop a conceptual design of reliable calibration plan including test sections, material needs, and processes; and evaluate the new process on different pavement types having different structural condition using calibration site data and available field data); (3) provide recommendations for implementation and application of the calibration proposed to demonstrate calibration ability and accuracy; and (4) identify future research needs.
