LTPP Literature References feature provides information on national and state level publications or other sources of information describing how LTPP data is being used.
LTPP Literature References
LTPP Literature References feature provides information on national and state level publications or other sources of information describing how LTPP data is being used.
There are 641 of 641 projects currently selected.
During development of the Long-Term Pavement Performance Program Accomplishments and Benefits 1989–2009 report, an extensive database of existing LTPP reports, products, and research results were compiled (through 2009). This is called the LTPP Literature References database.
The LTPP Literature References database includes documentation related to the following topics: Traffic Characterization and Prediction, Materials Characterization, Environmental Impacts of Pavement Design, Pavement Design, Pavement Management, Impact on Rehabilitation and Maintenance Strategies
Influence on Specific Design Features, and Additional Benefits. The documents are not present in this database but there is a bibliography that allows users to search for the documents.
Functions are provided for searching these documents by keywords or their classification. You can also access the bibliography list by topic in PDF format.
This report documents the procedure and steps used to back-calculate the layered elastic properties (Young's modulus and the coefficient and exponent of the nonlinear constitutive equation) from deflection basin measurements for all of the Long-Term Pavement Performance (LTPP) test sections with a level E data status. The back-calculation process was completed with MODCOMP4 for both flexible and rigid pavement test sections in the LTPP program. The report summarizes the reasons why MODCOMP4 was selected for the computations and analyses of the deflection data, provides a summary of the results using the linear elastic module (Young's modulus) for selected test sections, and identifies those factors that can have a significant effect on the results. Results from this study do provide elastic layer properties that are consistent with previous experience and laboratory material studies related to the effect of temperature, stress-state, and season on material load-response behavior. In fact, over 75 percent of the deflection basins analyzed with the linear elastic module of MODCOMP4 resulted in solutions with a root mean squared (RMS) error less than 2.5 percent. Those pavements exhibiting deflection-softening behavior with Type II deflections basins were the most difficult to analyze and were generally found to have RMS errors greater than 2 percent. In summary, the nonlinear module of MODCOMP did not significantly improve on the number of reasonable solutions, and it is recommended that nonlinear constitutive equations not be used in a batch mode basis.
The purpose of this volume is to provide statistical data that may be used to characterize the nature of the data in the various data sets. The specific data sets are the General Pavement Studies (GPS)-1, GPS-2, GPS-3, GPS-4, and GPS-5 data. Data were obtained from the Long-Term Pavement Performance (LTPP) database (also referred to as the LTPP Information Management System).
This paper, from the proceedings of the 52nd Annual Conference of the Canadian Technical Asphalt Association (CTAA), reports on a study that used waste tire crumb rubber materials (CRM) as modifiers in paving asphalts. The effectiveness of CRM as a modifier was studied in terms of the Superpave specification, phase separation tests, elastic recovery, Dynamic Shear Rheometer (DSR) phase angle reduction, and multiple stress, creep and recovery tests. The authors found that the use of CRM in the asphalt was limited by the 135 deg. C viscosity or by the pumping and handling capabilities when the CRM levels were higher than 10.5 percent. The optimal CRM level was determined to be at 10.5 percent for PG 58-31 base asphalt. This asphalt mixture met all of the Superpave requirements, as well as the common Superpave Plus requirements, in the areas of phase angle, elastic recovery, and multiple stress creep and recovery. The authors then applied the Long-Term Pavement Performance (LTPP) program and the Transportation Association of Canada (TAC) model to select optimal levels of CRM and suitable base asphalts for the specific climatic conditions, high-temperature grade bumping protocol, traffic volume, and speed for the City of Lethbridge, Alberta, Canada. They report on the findings from three test sections in different Lethbridge locations with various traffic volumes; these locations were paved from 2003 to 2005.
The knowledge of traffic loads is a prerequisite for the pavement analysis process, especially for the development of load-related distress prediction models. Furthermore, the emerging mechanistically based pavement performance models and pavement design methods (such as the anticipated "2002 Pavement Design Guide") require the knowledge of the load spectra acting on the pavement during its lifespan. This report describes a procedure for obtaining axle load spectra for Long Term Pavement Performance (LTPP) sections. The procedure has been demonstrated and evaluated by applying it to 12 LTPP sections for which different amounts of monitoring traffic data were available. Typically, for the majority of LTPP sections, there are only a few years for which the traffic load data were collected by automated equipment in the mid-1990s. To obtain axle load spectra for all in-service years, traffic loads must be projected: backcasted (for the years before the installation of traffic monitoring equipment) and forecasted (for the years after the automated equipment no longer provides data). This report also contains a review of the evolution of motor carrier technology (in terms of economical and political changes, regulatory changes in vehicle weights and dimensions, and engineering changes) and its impact on traffic loads, and a proposal to develop and use new summary statistical measures and tools for the management of load spectra. Major findings and recommendations include: (1) Traffic load projections for the majority of LTPP sites are feasible. (2) The accuracy and reliability of the traffic projections for many of the LTPP sites may not be as high as originally anticipated. (3) The involvement of State highway agencies (SHAs) in the traffic projection process is crucial. (4) The traffic projection process is very challenging and labor-intensive. The main reason for the labor-intensive process is the need to carry out extensive quality assurance activities to resolve inconsistencies in the reported traffic data. (5) The quality assurance process would greatly benefit from developing a knowledge base or a catalog documenting a typical range of traffic load variables. The process would also benefit from the availability of summary measures for traffic loads that are independent of pavement variables. (6) Traffic modeling and forecasting is a highly cost-effective way to extend limited sampling data and compensate for the lack of data. To obtain payback on the large investment in the traffic data collection effort by SHAs, it is necessary to allocate sufficient resources to utilize fully the available traffic data through the traffic prediction process. (7) It is recommended to proceed with carrying out traffic load projections for the selected LTPP sites (Phase 2 study). (8) Phase 2 study, and any future projection of traffic loads, should include the input from the representatives of SHAs.
Different backcalculation algorithms often give different answers in backcalculated pavement properties. This is because of the differences in the type of pavement models, solution search procedure, and deflection matching criteria used in the backcalculation analysis. Regardless of the theory applied and the backcalculation algorithm adopted, a logical basis of selection of the backcalculation procedure for practical applications would be to assess whether the backcalculated pavement properties could provide good estimates of the actual pavement properties. Today, the ease and the convenience of access to the Long-Term Pavement Performance (LTPP) database of actual measured data enable a highway agency to adopt this approach to select a backcalculation algorithm that meets its needs. With the LTPP-measured data, this approach was applied to evaluate the relative merits of four backcalculation algorithms (two versions of ILLIBACK, NUSBACK, and LTPP best-fit method) by a comparison of the computed elastic modulus of concrete pavement slab and the modulus of subgrade reaction of concrete pavements against the LTPP measured values. The performance of the four algorithms was greatly affected by the constraints imposed by the deflection theory adopted and was significantly dependent on their respective criteria used to match the computed and measured deflections. The number of sensors used in the backcalculation, as well as the choice of sensor configuration, can significantly affect the performance of the backcalculation algorithms.
Established as part of the Strategic Highway Research Program (SHRP) and now managed by the Federal Highway Administration (FHWA), the Long Term Pavement Performance (LTPP) program faces a significant challenge. Over the past decade, the LTPP program has developed a solid knowledge base for understanding how pavements perform. Its challenge throughout its second decade is to build on this foundation--to further the understanding of why pavements perform as they do. To address this challenge, FHWA has initiated several efforts that require the support and active participation of the States and Provinces. The intent of this document is to describe the challenge the LTPP program faces and explain the efforts underway to address this challenge. This document is presented in the following sections: Introduction; The Challenge; Addressing the Challenge; Critical Issues; and Future Opportunities.
Until recently, load-associated fatigue cracking of hot-mix asphalt (HMA) concrete-surfaced pavements that occurs in the wheelpath has been thought to always initiate at the bottom of the HMA layer and propagate to the surface. However, recent studies have determined that load-related HMA fatigue cracks can also be initiated at the surface of the pavement and propagate downward through the HMA layer. The penetration of water and other foreign debris into these cracks can further accelerate the propagation of the crack through the HMA surface layer. These studies indicate that environmental conditions, tire-pavement interaction, mixture characteristics, pavement structure, and construction practices are among the factors that influence the occurrence of this cracking. Hypotheses regarding top-down cracking mechanisms have been suggested; test methods for evaluating HMA-mixture susceptibility to cracking have been proposed; and preliminary models for predicting crack initiation and propagation have been developed.
Recent work completed under NCHRP 1-42 provided further review of some of the issues related to top-down cracking. However, additional research is needed to address these and other issues associated with top-down cracking and to develop mechanistic-based models for use in mechanistic-empirical procedures for design and analysis of new and rehabilitated flexible pavements.
The objective of this project is to develop mechanistic-based models for predicting top-down cracking in HMA layers.
The mechanistic-empirical study of pavement performance requires that immediate pavement responses due to tire loading be mechanistically computed for pavement structures, and the long-term pavement performance be related to the computed pavement responses. The problem becomes very complicated when variability is considered for loading, pavement and environmental conditions. A Monte Carlo simulation based mechanistic-empirical pavement analysis procedure was verified in this study. The complex tire-pavement interaction was more realistically handled and computed using finite element models and measured tire-pavement contact stress data. The computation time problem involved in pavement response computations was resolved by using a quick solution method that relates critical pavement responses to tire loading and pavement structural conditions. In the Monte Carlo simulation, different truck classes were drawn from the truck population empirically based on actual traffic volume data. Axle load spectra were characterized by actual axle load data collected at a weigh-in-motion site. Results from a survey of truck configurations were used to describe the distribution of truck tire pressure. Pavement structural parameters and relationships between material moduli and environment conditions were obtained from the LTPP data. The distress models developed in NCHRP Project 1-37A were employed to predict pavement performance. The simulation study estimates the effects of increased tire pressure and steering axle load on a typical pavement structure for 2 million truck passes. The Monte Carlo simulation method and models used in this study show a feasible approach to the development of flexible pavement design and analysis procedures.
The Federal Highway Administration (FHWA) has released version 3.0 of their DataPave software. The package, which is now available on two CD-ROMs, allows quick access to FHWA Long-Term Pavement Performance (LTPP) program data, including information on inventory, material testing, pavement performance monitoring, and other such data collected by the agency between 1987 and May 2001.
This project investigates the feasibility of using thick granular base for flexible pavement design in Ohio. The criteria considered include the performance criteria and life cycle economic analyses. The performance of different types of base layer design are compared using the Long Term Pavement Performance (LTPP) database. The focus is on the ability of achieving uniform dynamic deflections using Falling Weight Deflectometer (FWD) data. Based on FWD records from the LTPP database, the relative merits of different base type design are compared. The pavement performance is predicted using the "Mechanistic-Empirical Pavement Design Guide" (MEPDG) design software. A sensitivity study is conducted on the effects of granular base layer parameters on pavement performance. From the relative improvement in terms of pavement distress reduction, an optimal base layer thickness of 12 in. to 15 in. is identified. The use of thicker granular base (from the current 4 in. to 6 in. granular base currently used in Ohio to 12 in. thick granular base) is predicted to increase the pavement service life for around 30% using the criteria for common types of distresses. Life cycle analyses are conducted using a simplified model. The model indicates that for the typical Ohio flexible pavement sections, doubling the thickness of base layer, while causing higher initial construction cost, will result in life cycle cost savings. Thus performance predictions using the MEPDG and life cycle economic analyses support positively the use of granular base in flexible pavement design in Ohio. It is also found in this study that the climate model of the existing MEPDG design software does not adequately account for the regional climate conditions (such as freeze-thaw effects) effect on pavement performance. It is recommended to conduct further analyses of field performance data to validate the MEPDG model predictions. Finally, recommendations are provided on the specifications for screening the supply sources of granular materials for granular base construction.
Information Documentation page has the title as “Investigation of the Performance and Economic Benefits of Thick Granular Base for Flexible Pavement Design in Ohio.”
Drainage is the experimental factor about which conclusions from the SPS-2 experiments are most difficult to draw. This is because two experimental factors, base type and subdrainage, are confounded in the experiment. This paper describes the findings from NCHRP Project 1-34D, in which data from the LTPP SPS-2 (rigid) pavement design experiment were used to assess whether pavements with subsurface drainage systems (permeable base, collectors, and outlets) performed differently from pavements without subsurface drainage systems. The data analyzed included IRI, faulting, cracking, and deflection data from the LTPP database, as well as drainage system flow time measurements obtained from field testing. Whatever effect the base type/drainage factor has had on the SPS-2 pavement sections’ latest observed IRI values and rates of change in IRI over time is concluded to be due predominantly to differences in base stiffness. The potential effect of drainage is not necessarily ruled out, but no particular evidence was detected for the role of drainage, independent of the role of base stiffness, in the development of roughness in the SPS-2 pavements. Whatever effect the base type/drainage factor has had on the development of faulting in pavements in the SPS-2 experiment has been due to the stiffness of these bases compared to the lesser stiffness of the undrained dense-graded aggregate base. This conclusion is reinforced by the observation that the undowelled pavements with aggregate base developed more than twice as much faulting as undowelled pavements with drained or undrained stabilized bases, even those at the same sites. The stiffest base type in the SPS-2 experiment, lean concrete base, may have been good for performance in terms of roughness and faulting, but it had a pronounced detrimental effect on cracking performance, particularly in the thinner concrete slabs in the experiment. Sections with the weakest base type, undrained aggregate base, also had more cracking than sections with drained permeable asphalt-treated base. On the other hand, sections with undrained HMAC and CAM bases had even less cracking than sections with drained PATB. The above findings suggest that the differences in cracking observed to date are due not to drainage differences but differences in base stiffness.
Now in its second decade, research from the long-term pavement performance (LTPP) program continues to pay off with a host of new products designed to improve highway design, construction, and maintenance. These products include the LTPPBind software, which simplifies selection of the correct performance graded (PG) binder to use when implementing the Superpave mix design system. A series of videotapes presents the LTPP program's falling-weight deflectometer calibration procedures. Another series of three videotapes focuses on the LTPP studies' revised resilient modulus laboratory tests and procedures.
The Long Term Pavement Performance (LTPP) program in the United States was designed as a 20 year study of pavement performance. One aspect of the LTPP program is the monitoring of over 800 General Pavement Study (GPS) test sections that were established on in-service pavements in all fifty states of the United States and in Canada. A major data collection effort at the GPS sections is the collection of profile data that is performed annually. This paper presents the results of a study conducted to investigate the changes in roughness on: (i) GPS-1 experiment sections, which studies asphalt concrete pavements on granular base, and (ii) GPS-6B experiment sections, which studies asphalt concrete overlays of flexible pavements. The changes in roughness at test sections were investigated by using the International Roughness Index (IRI) as the roughness parameter. The test sections were classified according to environmental zones and the IRI trends for the group of test sections included in each zone were studied. Correlation analysis was conducted for GPS-1 sections in the dry freeze and the wet freeze zone between IRI and the factors that have an influence on roughness development. This paper presents a model that was developed to predict IRI for GPS-1 sections in the dry freeze zone. For the GPS-6B sections, the reduction in IRI due to the overlay was examined.
This report provides a summary of the Strategic Highway Research Program's Long-Term Pavement Performance (SHRP-LTPP) 5-year effort to better understand traffic's effect on pavement performance. The report also reviews the traffic data collection program over a 4-year period. It provides a connection with the reports and publications issued during the period by providing an extensive reference list. The design of this publication portrays the history of action by the Traffic Expert Task Group (ETG) and reflects their role in the traffic data collection and analysis program. The LTPP traffic database developed by this program will benefit state and federal highway agencies for many years. The LTPP central traffic database at the Transportation Research Board will be located parallel to the national pavement performance database, making the two readily accessible and usable to researchers.
This document describes the guidelines for the construction of test sections for the Strategic Highway Research Program (SHRP) Long Term Pavement Performance (LTPP) Specific Pavement Studies experiment SPS-6, Rehabilitation of Jointed Portland Cement Concrete Pavements. This experiment requires the construction of multiple test sections with similar details and materials at each of twenty-four sites distributed in the four climatic regions. The experiment has been developed as a coordinated national experiment to address the needs of the highway community at large, and not only the participating highway agencies. Therefore, it is important to control construction uniformity at all test sites to reduce the influence of construction variability on test results.
The objective of this study is to develop improved performance prediction models to be used for determining the additional pavement life that can be expected from application of a variety of jointed plain concrete (JPC) and jointed reinforced concrete (JRC) pavement rehabilitation methods and strategies ranging from minimal to maximal investment in the rehabilitation treatment. The treatments being studied include combinations of surface preparations, with and without asphalt concrete (AC) overlay, as well as crack and seat preparation with AC overlay. The study objective includes a determination of the influence of environmental region and initial pavement condition on the effectiveness of rehabilitation methods. The experimental designs and research plans presented here for Strategic Highway Research Program (SHRP) Long Term Pavement Performance (LTPP) Specific Pavement Studies experiment SPS-6, were adapted from the Specific Pavement Studies on restoration of jointed concrete pavements (JCP) and pretreated JCP with AC overlay originally described in the May 1986, “Strategic Highway Research Program Research Plans,” issued by the Transportation Research Board.
The study presented in this paper analyzed the development patterns of fatigue cracking shown in flexible pavement test sections of the Long-Term Pavement Performance (LTPP) Program. A large number of LTPP test sections exhibited a sudden burst of fatigue cracking after a few years of service. In order to characterize this type of LTPP cracking data, a survival analysis was conducted to investigate the relationship between fatigue failure time and various influencing factors. After dropping insignificant influencing factors, accelerated failure time models were developed to show the quantitative relationship between fatigue failure time and asphalt concrete layer thickness, Portland cement concrete base layer thickness, average traffic level, intensity of precipitation, and freeze-thaw cycles. The error distribution of the accelerated failure time model was found to be best represented by the generalized gamma distribution. The model can also be used to predict the average behavior of fatigue failures of flexible pavements.
A three stage validation process is described: the first two stages to be completed during its life and the final stage subsequent to March, 1993 as part of the ongoing Long Term Pavement Performance program. The first stage confirms that variation of asphalt binder properties identified as probable, significant determinants of pavement performance, yield physically reasonable, meaningful changes in relevant performance characteristics of asphalt-aggregate mixes. Details of the second stage validation are described including the direct correlation method and the indirect/mechanistic method. Post SHRP (Strategic Highway Research Program) third stage validation will offer the opportunity for refinement of those specifications through the LTPP Specification Pavement Study 9, Validation of Performance-Based Specifications and Mix Design and Analysis System.
Traffic data from the Long Term Pavement Performance Program (LTPP) were examined for accuracy. A method was developed that would be more accurate than the current algorithms and misapplications within the data. The same method can be made applicable to both automatic vehicle classification (AVC) and weigh-in-motion (WIM).
The Long-Term Pavement Performance Program (LTPP) has intensified its efforts to obtain sufficient quantities of research quality loading data at a number of Specific Pavement Studies (SPS) sites. As one part of this effort, the Federal Highway Administration (FHWA) has consulted with the Transportation Research Board LTPP Traffic Expert Task Group on a methodology to check the calibration of weigh-in-motion equipment. LTPP recognizes that there are multiple methodologies to actually calibrate WIM equipment, however, as with all other LTPP equipment protocols; a single methodology is being selected for verifying equipment calibration on a national basis. This provides a common reference for data users as to the quality standards expected of the data they have been provided. The methodology selected and the software referenced is included for participant reference. This document provides guidelines for verifying the accuracy of WIM systems for collecting LTPP traffic data at SPS 1, 2, 5, and 6 sites.
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