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    <title>Transport Research International Documentation (TRID)</title>
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    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
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    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Transport Research International Documentation (TRID)</title>
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      <link>https://trid.trb.org/</link>
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    <item>
      <title>A Mechanistic Approach to Utilize Traffic Speed Deflectometer (TSD) Measurements into Backcalculation Analysis</title>
      <link>https://trid.trb.org/View/1632761</link>
      <description><![CDATA[Backcalculation analysis of pavement layer moduli is typically conducted based on the Falling Weight Deflectometer (FWD) measurements; however, the stationary nature of FWD requires lane closure and traffic control. To overcome these limitations, a number of continuous deflection devices were introduced in recent years including the Traffic Speed Deflectometer (TSD). In this study, a mechanistic-based approach was developed to utilize TSD deflection measurements in the backcalculation analysis. The proposed approach is based on the 3D-Move software to calculate the theoretical deflection bowls corresponding to FWD and TSD loading configurations. Since 3D-Move requires the definition of the constitutive behavior of the pavement layers, cores were extracted from 13 sections in Louisiana and were tested in the laboratory to estimate the dynamic complex modulus of Asphalt Concrete (AC). Afterwards, 3D-Move generated deflection bowls were field-validated with an acceptable accuracy. The 3D-Move models were then used in a parametric study consisting of pavement designs of varying thicknesses and material properties and their corresponding FWD and TSD surface deflections were calculated. The results obtained from the parametric study were incorporated into a Windows-based software application, which uses Artificial Neural Network (ANN) as the regression algorithm to convert TSD deflections to the corresponding FWD deflections. This conversion would allow backcalculation of layer moduli using TSD measured deflections, as equivalent FWD deflections can be used with readily available tools to backcalculate the layer moduli.]]></description>
      <pubDate>Wed, 17 Jul 2019 17:57:37 GMT</pubDate>
      <guid>https://trid.trb.org/View/1632761</guid>
    </item>
    <item>
      <title>Development of ANN-GA program for backcalculation of pavement moduli under FWD testing with viscoelastic and nonlinear parameters</title>
      <link>https://trid.trb.org/View/1580402</link>
      <description><![CDATA[In this study, an Artificial Neural Network (ANN)-based backcalculating program combined with a Genetic Algorithm (GA) optimization algorithm was developed for backcalculation of flexible pavement layer moduli from Falling Weight Deflectometer (FWD) test. Axisymmetric finite element (FE) models were developed considering dynamic loading of FWD drops and viscoelastic and nonlinear material parameters of pavement layers. The FE models were used to generate the synthetic database that covers variations in material parameters, pavement structures, temperatures, and loading levels. The ANN-GA program was trained and verified using the synthetic database. The accuracy of backcalculation was evaluated with measured data from Long-Term Pavement Performance field testing sections. The ANN-GA program was found having acceptable accuracy through the verification and validation processes. The input variables of the ANN-GA program are available from FWD test including the deflections at different offsets, shape indicators of hysteresis loop (force-displacement curve), layer thicknesses, loading magnitudes, and air and surface temperatures. The ANN-GA possesses advantages over traditional iteration-based backcalculating program such as the elimination of seed moduli and consideration of complex material properties. More importantly, the backcalculated pavement layer parameters can be directly used for Mechanistic-Empirical design of pavement overlays.]]></description>
      <pubDate>Tue, 05 Mar 2019 16:03:23 GMT</pubDate>
      <guid>https://trid.trb.org/View/1580402</guid>
    </item>
    <item>
      <title>Prediction of Airfield Pavement Responses from Surface Deflections: Comparison Between Soft Computing Model and Traditional Backcalculation Approach</title>
      <link>https://trid.trb.org/View/1572275</link>
      <description><![CDATA[Heavy Weight Deflectometer (HWD) is commonly used in airfield pavement evaluation by means of imposing dynamic loading on pavement surface and measuring surface deflections. This study investigated traditional approaches and soft computing model for predicting airfield pavement responses from surface deflections measured under HWD testing conducted at National Airport Pavement Testing Facility (NAPTF). In the traditional approach, pavement layer moduli were backcalculated and then pavement responses were predicted based on multilayer elastic theory (MLE) and finite element (FE) method. The soft computing model was developed using Artificial Neural Network (ANN), which was trained using the synthetic database that contained surface deflections and critical strains calculated using different combinations of material property, layer thickness, HWD loading magnitude, and pavement temperature. It was found that the backcalculated moduli of asphalt surface layer were similar between MLE and FE methods; however, discrepancies were observed for the backcalculated moduli of unbound materials. In general, the traditional approach of backcalculation and forward calculation overestimated tensile strain in asphalt layers, especially for the pavement section with thin asphalt layer. On the other hand, the results show that the prediction accuracy of soft computing model is better than the traditional method as compared to field measurements. Further analysis of ANN model showed that Area Under Pavement Profile (AUPP) and Surface Curvature Index (SCI) had good correlations with critical tensile strain and shear strain in the asphalt layer, respectively.]]></description>
      <pubDate>Sat, 02 Mar 2019 15:41:13 GMT</pubDate>
      <guid>https://trid.trb.org/View/1572275</guid>
    </item>
    <item>
      <title>Rayleigh Damping Effects on the Subgrade's Apparent Non-Linearity</title>
      <link>https://trid.trb.org/View/1572253</link>
      <description><![CDATA[The effect of the subgrade’s apparent (superficial) non-linearity captured during Falling Weight Deflectometer (FWD) testing has been a major challenge for pavement engineers in trying to backcalculate reliable layer moduli. The current state of the practice backcalculation software accounts for the subgrade’s apparent non-linearity by using a non-linear stress-softening subgrade model or introducing an artificial stiff layer at a certain depth to obtain more realistic moduli. While these models tend to provide relatively acceptable results for typical pavements in many cases, they appear to be ineffective in backcalculating reliable moduli for rigid or thick and stiff flexible pavement structures. Dynamic models, which provide more realistic approximations, tend to focus on the viscoelastic behavior of the asphalt concrete layer and the non-linear behavior of the unbound layers. This paper focuses on identifying the shortcomings of the current models and developing a simple and robust model that approximates the overall pavement behavior. A two-dimensional (2D) axisymmetric finite element (FE) model was developed addressing the limitations of the existing models, and properly incorporating the subgrade’s damping behavior. The model was used for the backcalculation of layer moduli for flexible and rigid pavement structures built over the same subgrade at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF). The backcalculation with the new model produced reasonable layer moduli that are consistent with the type of material in each layer, and more importantly, it produced layer moduli that are almost equal for the same subgrade under the different pavement structures and types.]]></description>
      <pubDate>Sat, 02 Mar 2019 15:41:13 GMT</pubDate>
      <guid>https://trid.trb.org/View/1572253</guid>
    </item>
    <item>
      <title>Incorporation of Reliability into Airport Pavement Design Using Backcalculated Pavement Layer Moduli</title>
      <link>https://trid.trb.org/View/1558719</link>
      <description><![CDATA[Currently, several variations of Falling or Heavy Weight Deflectometer (F/HWD) equipment exist on the market. The Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF) Round-Up project provided an opportunity to examine different market available F/HWD equipment. This paper presents a case study of how the uncertainty of backcalculated in-situ moduli can be assessed and incorporated in the FAA Rigid and Flexible Iterative Elastic Layer Design (FAARFIELD) design procedure to determine appropriate pavement thicknesses. The mean values and standard deviations of backcalculated layer moduli were computed and then input into FAARFIELD using Rosenblueth’s procedure to predict the reliability of a 20-year pavement design performance. The research shows that the proposed procedure can be used as an alternative decision-making tool for airport engineers to more realistically predict pavement life using F/HWD data.]]></description>
      <pubDate>Mon, 31 Dec 2018 22:00:35 GMT</pubDate>
      <guid>https://trid.trb.org/View/1558719</guid>
    </item>
    <item>
      <title>Estimating fatigue endurance limits of flexible airfield pavements</title>
      <link>https://trid.trb.org/View/1508858</link>
      <description><![CDATA[In perpetual pavements, damage from bottom-up cracking can be limited to the top surface lift through using a very thick surface layer or a binder-rich intermediate layer. This can be attained by maintaining tensile strains at the bottom of the hot-mix asphalt (HMA) layer below a certain value known as the fatigue endurance limit (FEL). This paper presents a method for estimating a strain-based FEL for flexible airfield pavements. The proposed method is based on the concept that a 50% reduction in HMA layer modulus would indicate initiation of fatigue cracking. Falling weight deflectometer (FWD) testing results, collected from National Airport Pavement Test Facility (NAPTF) flexible pavement sections, were analyzed to determine at which loading pass each section had a 50% reduction in HMA layer modulus (N sub f50). NAPTF tensile strain data were also used to determine the tensile strain at N sub f50 for each pavement section by averaging the peak tensile strains. The proposed approach was validated by comparing its results to those obtained using a common FEL estimation model known as the rate of dissipated energy change (RDEC) model. To further verify the results of the proposed approach, peak tensile strain was plotted vs. number of loading cycles for all sensors. Using these plots, the peak tensile strain at which the variability in the strain gauge data increased was used as an estimate of a possible FEL. The N sub f50 tensile strains estimated using the proposed method were comparable to the values determined from RDEC and variability approaches.]]></description>
      <pubDate>Tue, 15 May 2018 22:18:16 GMT</pubDate>
      <guid>https://trid.trb.org/View/1508858</guid>
    </item>
    <item>
      <title>A Case Study: Assessing the Structural Durability and Functional Properties of Newly Constructed Modified or Lightly Cemented Pavements</title>
      <link>https://trid.trb.org/View/1495817</link>
      <description><![CDATA[The mechanistic empirical (ME) pavement design method has a long history and as such is favoured and specified by most road controlling authorities. Fatigue criteria for pavement layers treated with hydraulic binders are not as well established as asphalt mix criteria. Therefore, the long-term performance characteristics of modified/lightly cemented pavements are not always well defined and understood. Experience within New Zealand with “design and construct” procurement models indicates that pavement designers seem to have a short-term contractual focus; relying on initial strength gains from lightly cemented pavement layers to ensure compliance with contractual performance measures (deflections, layer stiffness, initial rut resistance, etc.). Unfortunately this approach is not always challenged, as contractual liability periods are relatively short – typically two years – compared to a 25 year design life. Thus, the risk that pavement design assumptions are not achieved or sustained beyond the contract liability period rests with the client. It is unclear if this is driven by designers in an attempt to reduce the pavement design thicknesses by assigning optimistic layer moduli to reduce cost, or redress possible deficiencies within material properties. Regardless, the New Zealand Transport Agency (NZTA) has experienced a number of early failures on newly constructed modified/lightly cemented pavements. These projects formed case studies, describing the impact of reduced moduli and the resulting redistribution of initial stresses and strains within the multi-layered system on pavement design life predictions. Falling weight deflectometer and annual high speed data were analysed to describe reduction in moduli.]]></description>
      <pubDate>Mon, 19 Feb 2018 12:01:34 GMT</pubDate>
      <guid>https://trid.trb.org/View/1495817</guid>
    </item>
    <item>
      <title>Effect of Moving Dynamic Loads on Pavement Deflections and Backcalculated Modulus</title>
      <link>https://trid.trb.org/View/1495041</link>
      <description><![CDATA[In this study, an existing finite layer program, ViscoWave, has been used for simulating the pavement deflections under a moving load. To simulate the deflections measured by Traffic Speed Deflection Devices (TSDDs), the moving frame analysis methodology was utilized to generate the deflections at various observation points moving with the load. A comparison between the deflections from a fixed point and a moving observation point is established initially under a constant load as well as a simple sinusoidal dynamic load. Then, the moving frame methodology is coupled with a mechanical vehicle model and a set of smooth and rough pavement profiles to demonstrate the effect of dynamic loading. The results indicated that dynamic loads may have a significant effect on the deflections measured by the TSDDs and the backcalculated modulus, especially for rougher pavements from which significant oscillation is generated in the vehicle motion and the resulting dynamic loads.]]></description>
      <pubDate>Mon, 05 Feb 2018 15:28:43 GMT</pubDate>
      <guid>https://trid.trb.org/View/1495041</guid>
    </item>
    <item>
      <title>Case Study Comparisons between Static and Dynamic Back-Calculation Results</title>
      <link>https://trid.trb.org/View/1495043</link>
      <description><![CDATA[Two case studies are presented in which both the static and dynamic backcalculation methodologies are utilized. It is demonstrated that the results from static backcalculation may not be within the expected range even when the corresponding error is low. The challenges associated with static methodology for backcalculating the modulus of thin layers are provided through the case study examples. On the other hand, it is also demonstrated that dynamic backcalculation showed reasonable results for the thin layers. Furthermore, it is also shown that the dynamic modulus values of multiple, viscoelastic layers were successfully backcalculated from dynamic analysis. However, the correlation between the static and dynamic backcalculation results were generally poor.]]></description>
      <pubDate>Mon, 05 Feb 2018 15:28:42 GMT</pubDate>
      <guid>https://trid.trb.org/View/1495043</guid>
    </item>
    <item>
      <title>Effects of Rayleigh Damping Parameters on the Subgrade's Apparent Nonlinearity</title>
      <link>https://trid.trb.org/View/1494306</link>
      <description><![CDATA[The effect of the subgrade’s apparent non-linearity captured during Falling Weight Deflectometer (FWD) testing has been a major challenge for pavement engineers in trying to backcalculate reliable layer moduli. The current state of the practice backcalculation software account for the subgrade’s apparent non-linearity by using a non-linear subgrade model or introducing an artificial rigid layer at a certain depth to obtain more realistic moduli. While these models tend to provide relatively acceptable results for typical pavements in many cases, they appear to be ineffective in backcalculating reliable moduli for rigid or thick and stiff flexible pavement structures. Dynamic models, which provide a more realistic approximation, tend to focus on the viscoelastic behavior of the asphalt concrete layer and the non-linear behavior of the unbound layers. This paper focuses on identifying the shortcomings of the current models and developing a simple and robust model that approximates the overall behavior of the entire pavement structure. A two-dimensional (2D) axisymmetric finite element (FE) model was developed addressing the limitations of the existing models, and properly incorporating the subgrade’s damping behavior. The model was used for the backcalculation of layer moduli for flexible and rigid pavement structures built over the same subgrade at the Federal Aviation Administration (FAA) National Airport Pavement Test Facility (NAPTF). The backcalculation with the new model produced reasonable layer moduli that are consistent with the type of material in each layer, and more importantly, it produced layer moduli that are almost equal for the same subgrade under the different pavement structures and types.]]></description>
      <pubDate>Sun, 21 Jan 2018 17:53:32 GMT</pubDate>
      <guid>https://trid.trb.org/View/1494306</guid>
    </item>
    <item>
      <title>Development of the pavement structural health index based on falling weight deflectometer testing</title>
      <link>https://trid.trb.org/View/1490057</link>
      <description><![CDATA[Non-structural parameters such as surface distresses and ride quality have commonly been used as functional indicators in the treatment selection process. However, transportation agencies have considered in recent years implementing structural capacity indicators into their pavement management system (PMS) and decision-making processes. The objective of this study was to develop a structural condition index for Louisiana, known as the Structural Health Index (SHI), on a scale from 0 to 100 that describes the structural integrity of the pavement structure based on the backcalculated layer moduli of in-service pavements as predicted from falling weight deflectometer (FWD) testing. Based on the developed methodology, the SHI is estimated by first backcalculating the layer moduli using a backcalculation software. Then, a sigmodal function is used to calculate the SHI. Evaluation and validation of the SHI was successful and demonstrated that the new index responded realistically to sections in poor and in good structural conditions. Furthermore, it was shown that the new index provided additional information that complements existing functional indices in PMS by successfully identifying structurally deficient sections. The implementation of the SHI into the Louisiana Department of Transportation and Development (LADOTD) decision matrix is demonstrated.]]></description>
      <pubDate>Mon, 11 Dec 2017 20:07:14 GMT</pubDate>
      <guid>https://trid.trb.org/View/1490057</guid>
    </item>
    <item>
      <title>Evaluation of Proposed Backcalculation Procedure in Indonesia Overlay Design Guide</title>
      <link>https://trid.trb.org/View/1461145</link>
      <description><![CDATA[Indonesia Directorate General of Highways’ overlay design guide Pd T-1-2002-B was developed by adopting the design procedure from 1993 AASHTO Design Guide. One evaluation in the guide was an evaluation of subgrade condition, in terms of elastic moduli, using backcalculation procedure from field deflection data. One main drawback of the backcalculation procedure in the guide is the use of adjustment factor (C) to make the calculated moduli conform to the measured ones. In addition, the guide also did not provide the evaluation of remaining capacity of surface layer that could be the important key for deciding the overall condition of the existing pavement. In this paper, a backcalculation procedure in the guide for determining remaining capacity of surface layer was proposed. For the sake of comparison, another backcalculation procedure based on best-fit trial-and-error approach was employed, and the results of both algorithm procedures were validated using measured pavement properties from Long-Term Pavement Performance (LTPP) database. The results of the study indicated that proposed procedure failed to produce the expected results. Besides, the high deviation between calculated moduli (from both backcalculation procedures) and measured ones leads to a recommendation of developing a better backcalculation procedure.]]></description>
      <pubDate>Wed, 03 May 2017 12:00:06 GMT</pubDate>
      <guid>https://trid.trb.org/View/1461145</guid>
    </item>
    <item>
      <title>LEAF – A New Layered Elastic Computational Program for FAA Pavement Design and Evaluation Procedures</title>
      <link>https://trid.trb.org/View/1405285</link>
      <description><![CDATA[A new computer program implementation of the layered elastic response equations has been written for use in Federal Aviation Administration (FAA) airport pavement design and evaluation computer programs. The program is written in Visual Basic (VB) 6.0 for Microsoft Windows 95, or higher, as a Dynamic Link Library with a defined interface. It can therefore be executed from programs written in other languages compiled for execution under Windows. Major objectives in writing the new program were to improve the efficiency of the computation of linear elastic pavement responses in the LEDFAA thickness design program and to provide a well-documented methodology and implementation suitable for further development when necessary. Wheel loads are modeled as circular loads with constant vertical pressure. Efficiency has been improved by structuring the program loops so that redundant computations are eliminated for multiple aircraft on a multiple-layered structure. This makes the computation time only very weakly dependent on the number of layers and the number of aircraft when all of the structure and aircraft information is passed to the program before execution. A code fragment is presented to illustrate the structure of the program loops. The use of Gauss-Laguerre integration, with offset of the layer origins, and part inversion in the solution of the matrix equations also improve efficiency. The development environment for LEAF was a computer program for backcalculating the layer modulus values of pavement structures represented by linear elastic layers of infinite horizontal extent. The requirements for calling the dynamic link library (DLL) from an application are illustrated by code excerpts from the backcalculation program.]]></description>
      <pubDate>Sun, 08 May 2016 19:24:50 GMT</pubDate>
      <guid>https://trid.trb.org/View/1405285</guid>
    </item>
    <item>
      <title>Early Structural and Functional Performance Trends of a High Performance Concrete Test Section</title>
      <link>https://trid.trb.org/View/1393399</link>
      <description><![CDATA[Minnesota Department of Transportation’s (MnDOT’s) 60-year concrete design is a material and structural design enhancement to produce concrete pavements of longer service life. The materials factors include low water cement ratio, high-pozzolan substitution, well-graded aggregate and stainless-steel dowels. After seven years of service, the high performance test cell of 60-year design concrete pavement test cell has not shown any performance concerns apart from those inherent in the construction process. Lesser strain was exhibited by this section in comparison to other pavements sections of shorter design life at the same research facility. This paper catalogues the various functional performance variables such as texture, friction and ride quality. It also discusses structural performance variables particularly load transfer efficiency, layer moduli and strain response from guided load testing to determine strain response. In all cases the strain levels were lower and the load transfer efficiencies were higher in the 60-year design cell compared to a 20 year design cell in the test facility. A controlled load testing also resulted in a 2 tailed t–test result validating lower strain responses in the 60-year design. While recommending continuous monitoring, this study concludes that the 60-year design objectives of reduced strain and sustenance of acceptable performance over a long time are still evident at this time.]]></description>
      <pubDate>Sun, 14 Feb 2016 16:01:15 GMT</pubDate>
      <guid>https://trid.trb.org/View/1393399</guid>
    </item>
    <item>
      <title>An Approach to Estimate Fatigue Endurance Limits of Flexible Airfield Pavements Using National Airport Pavement Test Facility Testing Results</title>
      <link>https://trid.trb.org/View/1336840</link>
      <description><![CDATA[In perpetual pavements, damage from bottom-up cracking can be limited to the top surface lift through using a very thick surface layer or a binder-rich intermediate layer. This can be attained by maintaining tensile strains at the bottom of the hot-mix asphalt (HMA) layer below a certain value known as the fatigue endurance limit (FEL). This paper presents a method for estimating a strain-based fatigue endurance limit for flexible airfield pavements. The proposed method is based on the concept that a 50% reduction in HMA layer modulus would indicate initiation of fatigue cracking. Falling Weight Deflectometer (FWD) testing results, collected from National Airport Pavement Test Facility (NAPTF) flexible pavement sections, were analyzed to determine at which loading pass each section had a 50% reduction in HMA layer modulus (N sub f50). NAPTF tensile strain data were also used to determine the tensile strain at N sub f50 for each pavement section by averaging the peak tensile strains. The proposed approach was validated by comparing its results to those obtained using a common FEL estimation model known as the Rate of Dissipated Energy Change (RDEC) model. To further verify the results of the proposed approach, peak tensile strain was plotted versus number of loading cycles for all sensors. Using these plots, the peak tensile strain at which the variability in the strain gage data increased was used as an estimate of a possible FEL. The N sub f50 tensile strains estimated using the proposed method were comparable to the values determined from RDEC and variability approaches.]]></description>
      <pubDate>Fri, 16 Jan 2015 08:28:47 GMT</pubDate>
      <guid>https://trid.trb.org/View/1336840</guid>
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