Pooled Fund Study Research Articles

Impact of Farm Equipment Loading on Rigid Pavement Performance Using Finite Element Analysis

The increase in agricultural product sales in recent years has led to the use of larger hauling and application equipment to transfer farm productions. This rapid shift in equipment size has raised a concern about their potential to cause significant damage in pavements and bridges. The study reported in this paper (part of a larger pooled fund study initiated in 2007) discusses the impact of farm equipment loading on rigid pavement performance based on Finite Element (FE) analysis. The study considered various types of farm equipment to determine the pavement responses and to quantify their damage on rigid pavement systems. The ISLAB2005 FE pavement response model was employed for numerical modeling and analysis of the test sections subjected to farm equipment loading. The results of FE analysis demonstrated that the rigid pavement damage caused by farm vehicles is governed by their axle weight rather than the gross vehicle weight. The FE analysis also showed that the damage resulting from farm equipment loading coupled with PCC slab curling could have a devastating effect on concrete pavement performance.

Evaluation of Compression Algorithms for 3D Pavement Image Data

A standard interchangeable data format was recently developed through the Transportation Pooled-Fund Study TPF-5(299) to meet different requirements and needs for two- and three-dimensional (2D/3D) pavement image data storage and exchange. Considering pavement images occupy large amounts of storage space, efficient compression algorithms for both 8-bit 2D and higher-bit 3D images become one of the key components for a successful implementation of the standard. Highway agencies and industry vendors exclusively use the Joint Photographic Experts Group (JPEG) or its successor JPEG 2000 standard for 2D image compression, while the compression of 3D 16-bit images remains to be proprietary. The goal of this paper is to evaluate suitable algorithms for compressing 3D pavement images. An overview of the state-of-the-art pavement image data collection technologies was performed, and the relevant image data formats were identified. Subsequently, five compression algorithms suitable for 16-bit image data were selected based on results from a comprehensive survey of the TPF-5(299) technical community. The compressions of several representative field images were implemented and evaluated in terms of the computation efficiency and retaining of image quality. The expected benefits of this study include facilitating standard and efficient pavement image data collection and accelerating the development of consistent pavement condition evaluation.

Empirical Models for Permanent Deformation of Subgrade Soils from the Data Collected at the Pavement Subgrade Performance Study

AbstractA national pooled-fund study supported by 19 states, the Federal Highway Administration, and the U.S. Army Corps of Engineers was conducted at the Cold Regions Research and Engineering Laboratory (CRREL) of the U.S. Army Corps of Engineers in Hanover, New Hampshire. The study, titled the Pavement Subgrade Performance Study (PSPS), aimed to develop failure criteria and prediction models for permanent deformation in the subgrade soil that incorporate the effects of soil type and moisture content. Full-scale pavement structures were built with the same crushed stone base and asphalt concrete surface layers on top of five subgrade soils. The soils were placed and compacted at three in situ moisture contents: the optimum and two other contents above the optimum. The pavements were subjected to full-scale accelerated pavement testing. An extensive volume of response and performance data was collected in the study. This paper presents the development of empirical models for permanent deformation of subgr...

Characterization of embrittlement temperature of asphalt materials through implementation of acoustic emission technique

The present study focuses on the application of an acoustic emission (AE) based laboratory test to evaluate low-temperature cracking performance of several types of asphalt materials in the context of a recently completed national pooled fund study on low-temperature cracking (LTC). Comparisons are made between AE test results and the critical cracking temperature of asphalt binders determined from Bending Beam Rheometer (BBR) test and Direct Tension Test (DTT), which are in turn compared to field observed thermal cracking in the corresponding test sections. Based upon our findings, recommendations are made as to the potential use of the AE-based technique in asphalt binder specification.

Multistate Safety Evaluation of Intersection Conflict Warning Systems

Intersection conflict warning systems (ICWSs) were evaluated under the FHWA Evaluation of Low-Cost Safety Improvements Pooled Fund Study. The ICWS strategy is intended to reduce the crash frequency by alerting drivers of conflicting vehicles on adjacent approaches at unsignalized intersections. The evaluation used a multistate database of geometric, traffic, and crash data for rural four-legged, two-way, stop-controlled intersections equipped with ICWSs in Minnesota, Missouri, and North Carolina. To account for potential selection bias and regression to the mean, an empirical Bayes before–after analysis was conducted by using safety performance functions (SPFs) for reference groups of similar intersections without ICWS installation. These SPFs also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the strategy. The aggregate results indicate statistically significant crash reductions at the 5% level for all crash types for two-lane-at-two-lane intersections and four-lane-at-two-lane intersections. For two-lane-at-two-lane intersections, the crash modification factors (CMFs) for total crashes, fatal and injury crashes, and right-angle crashes are 0.73, 0.70, and 0.80, respectively, and for four-lane-at-two-lane intersections, they are 0.83, 0.80, and 0.85, respectively. The benefit–cost (B:C) ratio estimated with conservative cost and service life assumptions is 27:1 for all two-lane-at-two-lane intersections and 10:1 for four-lane-at-two-lane intersections with post-mounted warning signs. The results suggest that the strategy, even with conservative assumptions on cost, service life, and the value of a statistical life, can be highly cost-effective. As this strategy is evolving, this study reflects installation practices to date.

Unified failure criterion for asphalt binder under cyclic fatigue loading

Defining failure and developing a unified failure criterion for the fatigue testing of asphalt materials remain a challenge. This study seeks to develop a failure criterion for the fatigue testing of asphalt binders under cyclic loading in the dynamic shear rheometer. Newly developed pseudo-strain energy (PSE)-based failure analysis is introduced for both the time sweep fatigue test and the accelerated linear amplitude sweep (LAS) test (AASHTO TP101). The presented methodology builds upon recent advances in the simplified viscoelastic continuum damage (S-VECD) modelling of asphalt mixtures. Trends in stored PSE have been proven to be effective in defining failure for the LAS tests of asphalt binders. This new proposed failure definition is material-dependent and, thus, is effective in capturing the benefits of asphalt modification for binder fatigue resistance. In addition, it is found that a unique relationship that is independent of loading history exists between the PSE release rate and fatigue life. The fatigue life predictions using this relationship and the S-VECD model are in reasonable agreement with the laboratory-measured fatigue life data and also generally relate well with the field fatigue performance measured in the FHWA-ALF (Federal Highway Administration – Accelerated Loading Facility) pooled fund study.

Strategies for Incorporating Higher Recycled Asphalt Pavement Percentages

Because there is a greater emphasis on promoting sustainable materials within transportation infrastructure, state agencies in the U.S. Northeast are investigating different strategies that will enable the use of higher percentages of recycled asphalt pavement (RAP) while not sacrificing the performance of the asphalt pavement. In particular, most state agencies in the Northeast are concerned with the fatigue and thermal cracking performance, as well as the general workability and handling of the higher-RAP-content asphalt mixtures when greater percentages are used. In conjunction with the Transportation Pooled Fund study TPF 5(230), Evaluation of Plant-Produced High-Percentage RAP Mixtures in the Northeast, three potential strategies were evaluated for incorporating higher RAP contents: using a softer asphalt binder grade to offset the stiff RAP asphalt binder, limiting the amount of RAP binder credited to the total asphalt content of the asphalt mixture, and using a performance-based specification that the high-RAP content mixture must meet for acceptance. The findings of the strategies through plant-produced mixtures, as well as case studies evaluated in detail through laboratory test procedures and analysis, are summarized. The project trials and results shown will, it is hoped, provide guidance to other agencies looking to increase the percentage of RAP used in their asphalt mixtures.

Validation of TMG Traffic Data Check Algorithms

Several state DOTs utilize the statistics presented in the Federal Highway Administration (FHWA)’s version of the traffic monitoring guide (TMG) to conduct weigh-in-motion (WIM) data quality checks for DARWin-ME traffic load spectra data preparation. Because the data check statistics in the guide were originally developed in the early 1990s, there is a need to reexamine its continuing use in up-to-date truck traffic streams. This paper aims to validate the TMG data check algorithms using WIM data from the long-term pavement performance (LTPP) special pavement study (SPS) traffic pooled-fund study. Cluster analysis is performed to identify similar traffic patterns, and the statistical summary for each data check criterion is obtained. Subsequently, the statistics based on the pooled fund data are compared to those recommended in the TMG. The results of the paper conclude that the data check criteria in the TMG guide are still valid for most of the sites; however, users should be alert that the guide also acknowledges WIM stations with exceptional patterns. This study presents a framework to check the suitableness of using the guide for such cases.

Impact of Various Trucks on Pavement Design and Analysis

This investigation assessed the sensitivity of Mechanistic–Empirical Pavement Design Guide (MEPDG) outcomes to normalized axle load spectra representing various loading conditions observed in the Specific Pavement Studies Transportation Pooled Fund Study of the Long-Term Pavement Performance program. The goal was to determine what vehicle classes and axle types with a wide range of axle loading conditions are likely to cause differences in pavement design outcomes when the MEPDG is used. Significant differences found in the MEPDG outcomes support the need for characterization of axle loading beyond a single default value for heavy trucks that dominate vehicle class distributions, especially for Class 9 trucks. The absence of differences for lightweight and under-represented trucks indicates that load spectra from various sites could be combined to develop a single default for some vehicle classes and axle types. The effect of bias in weigh-in-motion (WIM) axle weight measurements on the normalized axle load spectra estimates and the associated MEPDG outcomes was also investigated. It was found that drift in WIM system calibration leading to a more than 5% bias in mean error between true and WIM-measured axle weight could lead to significant differences in MEPDG design outcomes. These results were used to develop recommendations for creating axle loading defaults for the MEPDG.

Desarrollo de la nueva guía canadiense de diseño y gestión de infraestructura vial 2011: un resumen del estado de la práctica canadiense

En septiembre de 2009, la Asociacion de Transporte de Canada (Transportation Association of Canada, TAC) comenzo a desarrollar la version 2011 de la Guia de diseno y gestion de infraestructura vial (Pavement Asset Design and Management Guide, PADMG). El proyecto es un fondo de estudios auspiciado por mas de veinte organismos publicos canadienses entre los cuales se encuentran los diez Departamentos de Transporte provinciales, varias de las principales ciudades canadienses, diversas asociaciones industriales y el gobierno federal. El proyecto ha sido conducido por un consorcio canadiense compuesto por especialistas y academicos de todo el pais. El equipo esta compuesto por un variado grupo de profesionales de vasta experiencia en Canada en los diversos aspectos tratados en esta guia. La nueva Guia PADMG 2011 corresponde a una consolidacion del estado de la practica actual en Canada en materia de diseno y gestion de pavimentos para ingenieros, autoridades, administradores y tecnicos. Ademas, constituira una valiosa fuente informativa para estudiantes universitarios y de institutos de formacion tecnica, tanto en el pais como en el exterior. La guia destacara algunos aspectos industriales clave como la sustentabilidad, el cambio climatico y las innovaciones. En primer lugar, este trabajo presenta un resumen de los hallazgos encontrados en una encuesta realizada por una parte interesada con el fin de determinar el actual estado de la practica en Canada. La informacion recogida por esa encuesta cubre los principales conocimientos practicos del diseno y gestion de los pavimentos. La nueva Guia tendra 15 capitulos que comprenden la discusion sobre los principios de la gestion de infraestructura vial, requerimientos de datos, sustentabilidad, mantenimiento, materiales, diseno de caminos para alto y bajo volumen y analisis del ciclo de vida de los disenos de los pavimentos. El borrador del PADMG 2011 fue aprobado y el proyect

Evaluation of Nonintrusive Technologies for Traffic Detection, Phase 3

The third phase of the project on evaluation of nonintrusive technologies for traffic detection is a pooled-fund study in which field tests of selected nonintrusive sensors were conducted to determine their accuracy for volume, speed, and classification by length and by axle configuration. Sensors were evaluated in a variety of traffic and environmental conditions at two freeway test sites, with additional tests performed at both signalized and unsignalized intersections. Emphasis was placed on urban traffic conditions, such as heavy congestion, and varying weather and lighting conditions. Although previous tests evaluated sensors’ volume and speed accuracy, the current generation of nonintrusive sensors introduces robust classification capabilities. New technologies, such as ground-mounted laser sensors and improved radar, contribute to this improved performance. Overall, the sensors performed better than their counterparts in previous phases of research for volume and speed accuracy. However, the additional classification capabilities had mixed results. The length-based sensors were generally able to report vehicle lengths within their tolerances, and the axle-based sensors provided accurate interaxle measurements, but significant errors were found in relating these data with a standardized classification scheme, such as FHWA's 13-class scheme. Agencies must perform independent analysis of their classification schemes to determine whether nonintrusive sensors will provide acceptable results.

Safety Effectiveness of Advance Street Name Signs

Low-cost safety strategies that states may implement as part of their Strategic Highway Safety Plans need to be evaluated. FHWA organized a Pooled Fund Study of 26 states to evaluate several low-cost safety strategies, including the installation of advance street name signs at signalized intersections. This study investigates whether advance street name signs reduce crashes related to way-finding (i.e., rear-end and sideswipe crashes) at signalized intersections. Geometric, traffic, and crash data were obtained for signalized intersections at 82 sites in Arizona, 65 sites in Massachusetts, and 46 sites in Wisconsin. To account for potential selection bias and regression to the mean, an empirical Bayes before–after analysis was used. The analysis found no significant effect of advance street name signs on total crashes. However, the analysis indicated a significant reduction in sideswipe crashes, including a 27% reduction in Massachusetts and a 10% reduction for the three states combined. A disaggregate analysis was also conducted to identify differential effects. On the basis of conservative cost estimates, a reduction of just 0.01 crash per intersection year would achieve a 2:1 benefit–cost ratio. Given the low cost of this strategy and the potential to enhance way-finding, the use of advance street name signs is justified, particularly at three-legged intersections and locations with relatively large average annual daily traffic or a large expected number of crashes.

Low-Cracking, High-Performance Concrete Bridge Decks

Cracks in concrete bridge decks provide easy access for water and deicing chemicals that shorten the life of the deck, and field surveys show that the problem has become progressively more severe since at least the 1980s. A two-phase, 10-year Pooled Fund study to minimize cracking in bridge decks is now under way. Twenty bridge decks have been constructed in the program to date. Comparison with conventional decks shows that the techniques embodied in low-cracking, high-performance concrete (LC-HPC) bridge deck specifications have been highly successful in reducing cracking in bridge decks. The results also show that high-slump high-strength concretes result in greater cracking in bridge decks than low-slump, moderate-strength concretes and that concrete temperature control and early application of curing counteract the negative effects of casting concrete under high-temperature conditions. Early owner and contractor buy-in is needed for successful LC-HPC bridge deck construction, and top performance requires the adherence to all aspects of the specifications.

Safety Effectiveness of Lane and Shoulder Width Combinations on Rural, Two-Lane, Undivided Roads

There is a need to evaluate low-cost safety strategies that states may implement as part of their Strategic Highway Safety Plan. FHWA organized a pooled fund study of 26 states to evaluate several low-cost safety strategies, including the reallocation of total paved width. This study identifies whether it is safer to increase lane width or increase shoulder width given a fixed total width. Geometric, traffic, and crash data were obtained for more than 52,000 mi of roadway in Pennsylvania and Washington State. A case-control approach was applied to evaluate the safety effectiveness of various lane–shoulder configurations. There was a general reduction in the odds ratio as total paved width, lane width, and shoulder width increased individually; this is consistent with previous research. However, the primary research objective was to estimate the safety effectiveness of reallocating a fixed total paved width. Individual state results did not indicate a clear trade-off between lane and shoulder width for a fixed total width. Supplementing the results of this study with previous research, crash modification factors (CMFs) are provided for several lane–shoulder combinations. The selected values present a more apparent trade-off, indicating a slight benefit to increasing lane width for a fixed total width. Importantly, the results differ from other studies that developed CMFs without considering the interaction between lane and shoulder width, including those studies currently referenced in the Highway Safety Manual. This raises the question of whether CMFs should reflect the interaction between lane and shoulder width.

Benefit–Cost Analysis of Maintenance Decision Support System

The pooled fund study of the Maintenance Decision Support System (MDSS), led by South Dakota and now including 13 state departments of transportation, developed an operational MDSS for winter maintenance. While the MDSS is generally perceived to be beneficial, it is important to determine more formally the tangible benefits and costs associated with its implementation and to determine whether it is a good investment. This paper presents the results of a benefit–cost analysis of the pooled fund MDSS. The development of the analysis method includes the identification of benefits and costs, the definition of base case and alternatives, and the development of a benefit–cost model. A base case (without MDSS) and two other alternatives (with MDSS) are defined for the analysis. The developed method consists of two parallel modules: a baseline data module and a simulation module. Results from a case study applying this method show that the implementation of MDSS brings more benefits than costs.

Safety Evaluation of Installing Center Two-Way Left-Turn Lanes on Two-Lane Roads

FHWA organized a pooled fund study of 26 states to evaluate low-cost safety strategies as part of its strategic highway safety effort. One of the strategies chosen to be evaluated for this study was the installation of center two-way left-turn lanes (TWLTLs) on two-lane roads. Geometric, traffic, and crash data were obtained for 78 sites (21.3 mi) in North Carolina, 10 sites (6.0 mi) in Illinois, 31 sites (6.8 mi) in California, and 25 sites (13.2 mi) in Arkansas. Empirical Bayes methods were incorporated in a before–after analysis to determine the safety effectiveness of installing the TWLTLs. There was a statistically significant reduction in total and rear-end crashes in each of four states whose installations were evaluated. Rural installations were found to be more effective in reducing crashes than were urban installations in each of the four states. The general conclusion of this research is that TWLTLs can be a cost-effective treatment for two-lane rural locations, especially those with a high frequency of rear-end collisions involving a lead vehicle desiring to make a left turn.

Safety Evaluation of Flashing Beacons at Stop-Controlled Intersections

FHWA organized a pooled fund study of 26 states to evaluate low-cost safety strategies as part of its strategic highway safety effort. One of the strategies chosen to be evaluated was the installation of flashing beacons at stop-controlled intersections. The intent of flashing beacons is to reduce the frequency of crashes related to driver unaware-ness of stop control. Geometric, traffic, and crash data were obtained at stop-controlled intersections for 64 sites in North Carolina and 42 sites in South Carolina. Empirical Bayes methods were incorporated in a before–after analysis to determine the safety effectiveness of installing flashing beacons while accounting for potential selection bias and regression-to-the-mean effects. Overall, installation of flashing beacons in North Carolina resulted in statistically significant reductions in total, angle, and injury-plus-fatal crashes. The intersections in South Carolina experienced little change following the introduction of flashing beacons, but the combined results from both states still indicated a statistically significant reduction in angle and injury-plus-fatal crashes. An economic analysis indicated that standard flashing beacons can achieve a 2:1 benefit–cost ratio.

Safety Effectiveness of “Stop Ahead” Pavement Markings

There is a need for rigorous evaluation of low-cost safety strategies that states may implement as part of their strategic highway safety plans. Highway safety funds are limited, so it is important to identify cost-effective strategies. FHWA organized a pooled-fund study of 26 states to evaluate low-cost safety strategies; “Stop Ahead” pavement markings were one strategy selected for investigation. Geometric, traffic, and crash data were obtained for 175 intersections with “Stop Ahead” pavement markings in Arkansas, Maryland, and Minnesota. Similar data were obtained for reference sites within each state. An empirical Bayes approach was incorporated in a before–after study design to evaluate the safety effectiveness of the “Stop Ahead” pavement markings. An aggregate analysis indicated a significant reduction in total crashes for Arkansas, Maryland, and the two states combined. There was also a significant reduction in right-angle and rear-end crashes for Arkansas and a general reduction in injury crashes. A disaggregate analysis indicated that crash reductions are significantly greater at three-legged intersections than at four-legged intersections. The strategy was also more effective at intersections with all-way stop control. Given the low cost of this strategy, even with conservatively high cost estimates, only a modest reduction in crashes is needed to justify its use. On the basis of the estimated safety effectiveness, the necessary crash reduction is easily achievable.

Verification and Calibration of VESYS5W Fatigue Cracking Model Using Results from Accelerated Pavement Testing

Abstract Cost effective design methodology demands accurate performance modeling. Fatigue cracking is one of the major performance indicators in flexible pavement systems. Through literature review, a decision was made to modify the fatigue cracking model in the original VESYS5 program. The revised model in VESYS5W has the same basic form as suggested by the Asphalt Institute (AI) and the 2002 Mechanistic-Empirical Pavement Design Guide (MEPDG). The main challenge in modeling fatigue cracking is to determine appropriate input parameters. Efforts were made to compare the experimental results of full-scale accelerated pavement testing (APT) to the VESY5W predictions using the material parameters suggested by AI and the 2002 MEPDG. The test data employed in this paper are obtained from the full-scale APT conducted by the Federal Highway Administration (FHWA) under a national pooled fund study TPF-5(019). Test results from five lanes at testing temperatures of 19°C were utilized in the comparisons. It was found that the VESYS5W prediction using the material parameters from 2002 MEPDG yielded a much better fit to the experimental results than those using AI material parameters. The VESYS5W predictions using the AI material parameters always underestimated the fatigue cracking life. To match experimental results, shift factors were applied. The shift factors ranged from 0.48 to 3.1 for the predictions using the material parameters from the 2002 MEPDG. However, the shift factors for the AI material parameters ranged from 3.6 to 14.4. In summary, VESYS5W predictions using 2002 MEPDG material parameters provided satisfactory fits to the experimental results with relatively small (⩽3.1) shift factors. Based on the FHWA’s APT test results and the VESYS5W analyses, two equations are recommended for prediction of fatigue cracking in pavements with conventional mix and with asphalt modifier.

Development of Pavement Performance Models to Account for Frost Effects and Their Application to Mechanistic–Empirical Design Guide Calibration

Although it has long been recognized that the presence of frost is a factor in the performance of pavements, little national research has been conducted to study the long-term performance differences caused by frost exposure. To address this concern, a pooled fund study, Effect of Multiple Freeze Cycles and Deep Frost Penetration on Pavement Performance and Cost, was conducted under the direction of the FHWA Long-Term Pavement Performance data analysis program. This study not only explored the effect of frost on pavements but also differentiated between two types of frost exposure: deep frost penetration, remaining present throughout the winter months, and freeze–thaw cycling, occurring multiple times during the frost season. Performance models were developed to evaluate the independent effects of these two freezing conditions on long-term pavement performance. These models were used to make comparisons of predicted fatigue, rutting, and roughness measures in different environmental settings. Predictions revealed that significant differences existed among the various climatic scenarios. An evaluation also was conducted on the application of the models for regional calibration of the NCHRP 1-37A design procedure for locations where measured performance data are not available. An example shows that the models can be used as an effective calibration tool.