bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging Indices for Quantification of Shape, Angularity, and Surface Texture of Aggregates
Authors: Kuo Chun-Yi , Freeman Reed B.
Published: April 2007

Three image indices are presented that characterize aggregates in a hierarchical scheme involving overall shape (or form), roundness of corners, and particle surface texture. The corresponding dimensionless image indices are called aspect ratio, angularity, and roughness, respectively. Calculating these indices requires that image-analysis techniques be used to find the following data for a sample of two-dimensional particle images: shortest and longest dimensions, perimeters, convex perimeters, and perimeters of ellipses with areas equivalent to those of the associated particles. To demonstrate the usefulness of these three dimensionless indices, selected sieve-size fractions for 25 fine-aggregate sources were subjected to image-analysis testing and to uncompacted void testing (ASTM C1252). Both uncompacted void contents and image-analysis indices could generally differentiate between natural sands and crushed fine aggregates. However, the image-analysis indices provided additional useful information. For example, the image-analysis results identified that two sources of crushed fine aggregates had relatively low uncompacted void contents because they had relatively smooth surface textures or relatively low aspect ratios. In addition, the image-analysis results were able to distinguish morphological differences between aggregate sources that were measured to have similar uncompacted void contents.
Uncompacted Voids and Particle Index Tests for Evaluating Coarse Aggregate
Authors: Shabbir Hossain M. , Parker Frazier , Kandhal Prithvi S.
Published: April 2007

Coarse-aggregate angularity and surface texture are properties specified under the SuperpaveTM mix design system. To control specification requirements, the fractured-face count test is suggested. The use of a more objective test was investigated. Uncompacted voids and index of aggregate particle shape and texture tests were studied to measure coarse-aggregate angularity. The gradation of the sample has an obvious influence on both test results. Ways to separate the effect of gradation from aggregate angularity were studied. Viable options include testing a standard graded sample and computing a weighted average from tests of individual size fractions based on the gradation of the blend. When comparing aggregate sources, either option produces a comparable evaluation, but testing standard graded samples saves time. On the other hand, the weighted average is more appropriate for evaluating an aggregate blend. The index of aggregate particle shape and texture test and the uncompacted voids test provide comparable measures of coarse aggregate angularity and surface texture.
Integrated Transportation and Land Use Policy Analysis for Sacramento, California
Authors: Putman Stephen H. , Zam Ahmad Hasnol Zam , Choi Ki-Man , McCarthy William P. , Yan Yongmin
Published: April 2007

Several transportation policy scenarios being discussed in the Sacramento, California, region were examined in detail by using an integrated set of transportation and land use models. The scenarios examined included a light-rail transit system, high-occupancy-vehicle lanes, and a highway beltway. These scenarios were compared with a baseline forecast that included built and committed transportation facilities out to the year 2020. The model systems used were the METROPILUS land use modeling system and the MINUTP transportation modeling package currently in use by the Sacramento Area Council of Governments. The model packages were linked in such a way as to allow an equilibrium adjustment process to be calculated within each of the 5-year time periods between the 1990 base year and the 2020 forecast horizon. The results of these analyses show small but significant differences in the outcomes of the several scenarios examined. Overall the results are consistent with expectations and illustrate the robust applicability of the method of approach, while at the same time raising some interesting questions as to exactly what issues might be encountered if any attempt were made to implement these scenarios in the region.
Pretest-Posttest Strategy for Researching Neighborhood-Scale Urban Form and Travel Behavior
Authors: Krizek Kevin J.
Published: April 2007

Communities are increasingly looking to land use planning strategies based on a less auto-dependent urban form to reduce the need for travel, especially drive-alone travel. In recent years, several studies have attempted to test the impact urban form has on travel behavior to determine if such designs are warranted. The results of these studies are mixed because of several shortcomings. Some shortcomings can be attributed to data availability; others are a product of the techniques used to characterize urban form or travel. Still other shortcomings are embedded in the strategies employed, using cross-sectional travel data and correlating travel outcomes with urban form. The line of research is being extended, aimed at isolating the influence of urban form on travel behavior; a new research strategy is presented using longitudinal travel data in concert with detailed measures of travel behavior and urban form. Data sources from the Puget Sound are described and a research strategy is presented that permits a pretest-posttest analysis of households’ travel behavior before and after they changed residential location. Early results show few changes in household travel behavior after a move, suggesting that attitudes toward travel are firmly entrenched and postmove travel provides little insight into how changes in urban form affect travel. Although a pretest-posttest makes valiant strides in shedding new light on the matter, the complex phenomenon being addressed requires myriad approaches. More comprehensive research techniques and even research approaches based on different different traditions are much needed to better understand how urban form and travel interact.
Characterizing Asphalt Pavements for Performance
Authors: Lytton Robert L.
Published: April 2007

Having fast computers with lots of memory makes it possible to make performance predictions using mechanics, which simply could not have been done even as recently as 3 or 4 years ago. This trend can be expected to continue. Pavement materials, whether asphalt concrete, base course, or subgrade, can now be characterized in realistic ways that were simply unavailable to pavement engineers. The dependence of these materials on stress state, moisture, temperature, strain rate, and damage is what has made their characterization difficult, if not impossible. This complexity has posed an almost insuperable problem for computational mechanics and for the linkage of these properties to construction specifications on the one hand and performance of in-service pavements on the other. Although these tasks will never be simple, the tools to work on them are becoming more adequate. Some examples are given of how one can proceed to simplicity through complexity in several areas that are important to pavement performance. In every case, one must be able to measure a property of the material that can be used as input to a computer program, principally a finite element program, that allows material properties to change from point to point. Several examples are given in the categories of material properties, material behavior, materials testing in the laboratory, nondestructive testing in the field, and performance prediction models. Laboratory testing, materials characterization and properties, nondestructive testing of pavements in service, construction specifications, pavement variability and reliability, field data collection, performance prediction modeling, and prediction of pavement response and distress with modern computer methods—taken individually, these subjects look complex. Combined with the glue of mechanics, they are simplicity itself. And they confirm Alfred North Whitehead’s principle, “The only simplicity that can be trusted is that which lies beyond complexity.”
Evaluation of Open-Graded Friction Course Mixtures Containing Cellulose Fibers
Authors: Allen Cooley L. , Ray Brown E. , Watson Donald E.
Published: April 2007

Open-graded friction courses (OGFCs) are special-purpose mixes used to improve friction, minimize hydroplaning, reduce splash and spray, improve night visibility, and lower pavement noise levels. OGFCs typically utilize a gap grading for aggregates and a low percentage of filler. The asphalt content for OGFCs is generally slightly higher than that for dense-graded mixes. The combination of uniform grading, low filler, and normal OGFC asphalt content can lead to the draining of asphalt binder from a mix (typically called draindown) during transportation and laydown procedures. States that use OGFC typically utilize fibers to help prevent draindown. Generally, these states have specified mineral fibers over organic fibers because of concern that organic fibers (cellulose) would absorb water and lead to moisture problems in the field. A study was conducted to evaluate the use of cellulose fibers in OGFC mixes. The study entailed both a field phase and a laboratory phase. Field work entailed conducting a visual distress survey of six experimental OGFC pavements placed in Georgia during 1992. These pavements contained six different combinations of binder polymer and additives. Laboratory work entailed preparing OGFC mixes with both cellulose and mineral fibers and performing numerous moisture sensitivity tests. Results indicated that cellulose fibers performed as well as mineral fibers in OGFC mixes.
Flagstaff I-40 Asphalt Rubber Overlay Project: Nine Years of Success
Authors: Way George B.
Published: April 2007

In 1990 the Arizona Department of Transportation designed and constructed a large-scale asphalt rubber (AR) test project in Flagstaff, Arizona, on the very heavily trafficked Interstate 40. The purpose of the test project was to determine whether a relatively thin overlay with AR could reduce reflective cracking. AR is a mixture of 80 percent hot paving-grade asphalt and 20 percent ground tire rubber. This mixture is also commonly referred to as the asphalt rubber wet process or McDonald process. The overlay project was built on top of a very badly cracked concrete pavement that was in need of reconstruction. The AR overlay has performed beyond original expectations. After 9 years of service the overlay is still virtually crack free, with good ride, virtually no rutting or maintenance, and good skid resistance. The benefits of using AR on this project represent about $18 million in construction savings and 4 years’ less construction time. Strategic Highway Research Program SPS-6 test sections built in conjunction with the project further illustrate the very good performance of AR. Results of this project have led to widespread use of AR hot mixes throughout Arizona. On the basis of this work over 3333 km (2,000 mi) of successfully performing AR pavements have been built since 1990.
Selection and Evaluation of Field Permeability Device for Asphalt Pavements
Authors: Allen Cooley L. , Ray Brown E.
Published: April 2007

Results of a study conducted to select, standardize, and evaluate a device to estimate the in-place permeability of hot-mix asphalt (HMA) pavements are presented. The study consisted of evaluating four different field permeameters in order to select and standardize a device that was correlated with laboratory permeability results, would provide repeatable results, and was easy to use. Additional testing on five HMA pavements was conducted with the selected device in order to evaluate the relationship between in-place pavement density and field permeability. The study entailed visiting three ongoing construction projects and conducting field permeability tests on newly compacted HMA pavements with each device. Also at each project, cores were obtained from which the laboratory permeability was determined. The data from each project were analyzed to determine which field permeameter correlated best with laboratory permeability, provided the most repeatable results, and was easy to use. Results of this study indicated that two permeameters did not show significant differences in results when compared with laboratory permeability results and had approximately the same amount of repeatability. For this reason, a field permeameter was selected on the basis of ease of use. This selected device was then taken to five additional HMA construction projects. At each project, field permeability testing was conducted, and the in-place density of pavements was obtained from cores. Relationships between in-place air voids and field permeability for all five projects were good: R2-evalues ranged from 0.63 to 0.82.
Asphalt Permeability Testing in Virginia
Authors: Maupin G.W.
Published: April 2007

Because of high air voids, long-lasting damp spots on pavement surfaces, and problems that other states have had with permeable coarse Superpave mixes, the Virginia Department of Transportation (VDOT) decided to investigate the permeability of its Superpave mixes. As part of this study, VDOT also tested other asphalt mixes. Falling-head permeability tests were performed on pavement cores to determine the general permeability of the mixes. The permeability of some of the pavement cores was compared with the permeability of specimens made in the laboratory through the use of mixtures sampled during construction to determine whether laboratory specimens could be used to predict pavement permeability. The primary purpose of this investigation was to determine the general magnitude of permeability for mixes being used by VDOT, with an emphasis on Superpave mixes. A large percentage of the field cores contained excessive voids, resulting in excessive permeability. Each mix had a unique voids-permeability relationship. Mixes that were composed of large aggregates required fewer voids to achieve an acceptable level of permeability. In four of five cases, the results of laboratory tests were generally quite successful in indicating field permeability. The preliminary permeability testing demonstrates the importance of achieving low voids in the field and will help in the future development of density specifications and possibly in the establishment of permeability requirements. It is recommended that the permeability test continue to be used to help set such limits.
Effects of Testing Time and Confining Pressure on Falling-Head Permeability Tests of Hot-Mix Asphalt Concrete
Authors: Hall Kevin D. , Cruz Josue , Ng Hooi
Published: April 2007

Superpave implementation has resulted in increased interest in the permeability of hot-mix asphalt concrete. Relatively open-graded Superpave mixes have given rise to concern about premature pavement failures due to increased water infiltration from the surface. Arkansas is investigating the use of a falling-head permeability test to evaluate Superpave mixes with respect to potential performance problems caused by increased permeability. The initial phase of the project concerns the development of laboratory testing procedures and equipment. Superpave field mixes from projects in Arkansas were sampled to investigate permeability testing parameters. In addition, compacted test specimens from a round-robin study of permeability were included in the testing matrix. For the Arkansas mixes, loose mix sampled at the hot-mix plant was compacted using the Superpave gyratory compactor. Field cores were also taken from completed pavement sections. Permeability tests were conducted on all samples to investigate the effect of testing time (15, 30, 45, and 60 min) and confining pressure (69 and 96.5 kPa) on the measured permeability values. Results of the testing suggest that neither the time interval used in measuring the head drop in a falling-head test nor the confining pressure used in the flexible wall testing apparatus significantly affects test results. These findings will greatly simplify testing methods and setup, making the test more attractive as a relatively routine tool for the mix design laboratory.
Cellular Telephone Conversation While Driving: Effects on Driver Reaction Time and Subjective Mental Workload
Authors: Tokunaga Roberto Abraham , Hagiwara Toru , Kagaya Seiichi , Onodera Yuki
Published: April 2007

The effects of conversation through a cellular telephone while driving on driver reaction time and subjective mental workload (SMWL) were investigated. Two vehicles equipped with measurement devices were used to measure reaction time. The drivers’ SMWL was measured by the National Aeronautics and Space Administration Task Load Index procedure. The experiment was conducted on an expressway in Japan. Thirty-one subjects participated in the experiment; 19 were young and 12 were elderly drivers. Each subject was asked to follow a leading vehicle and to keep a constant distance while following. The subjects performed four tasks: ( a) following a leading vehicle, ( b) operating a cellular telephone while following the leading vehicle, ( c) performing a simple conversation task, and ( d) performing a complex conversation task on a cellular telephone with the experimenter while following the leading vehicle. The results of these experiments indicated that the performance of the telephone tasks increases the reaction time and SMWL of the drivers, as was shown in a previous study. The results also indicated that the complex conversation task produced an increase in reaction time as compared to the simple conversation task, independent of age group. Furthermore, the experiment indicated that the SMWL also increased significantly in the complex conversation task as compared to the other tasks.
Aggressive Driving and Road Rage Behaviors on Freeways in San Diego, California: Spatial and Temporal Analyses of Observed and Reported Variations
Authors: Sarkar Sheila , Martineau Alanna , Emami Mohammad , Khatib Mohammad , Wallace Karen
Published: April 2007

The California Highway Patrol in San Diego County receives cellular telephone calls reporting unsafe driving. The content of the calls varies, with drivers complaining about speeding cars driving over 161 km/h (100 mph) and other drivers weaving and cutting off or tailgating. In some cases, the driving conditions were even more volatile with drivers describing harassment, assaults with a weapon, or running other vehicles off the road. There were about 1,987 reported incidents from the freeways of San Diego for the months of April, June, and September 1998. The information received by the dispatchers was tabulated and put into five different categories. Analyses indicated that 24.6 percent of the calls were for “Aggressive Driving 1” (speeding plus some other behavior, such as unsafe lane changes or passing); “Aggressive Driving 2” (weaving and cutting) was reported most frequently (27.1 percent of all calls); about 12.5 percent of the calls were for “Aggressive Driving 3” (tailgating); “Speeding Alone” calls comprised 19.8 percent of the total; and the rest were for “Road Rage” (16.1 percent). Of the 1,987 calls, 33 percent were generated on Interstate 5, the busiest and longest in the county, followed by Interstate 15, which accounted for 22 percent of the calls. The high number of calls can be attributed to the high average daily traffic volumes at each interchange and the longer interstate lengths. Similarly, Interstate 8 seemed to have a lower number of calls than expected, because the urban portion of the freeway is not as long and the remaining distance had fewer vehicles at each interchange. This was further corroborated and both volume and length were robustly correlated with the number of phone reports per freeway. Additionally, chi-square tests indicated that the time of the day and day of the week influenced the type and number of calls received.
Attention-Based Model of Driver Performance in Rear-End Collisions
Authors: Brown Timothy L. , Lee John D. , McGehee Daniel V.
Published: April 2007

Several driver-performance factors contribute to rear-end collisions—driver inattention, perception-reaction time, and limitations of the human visual system. Although many evaluations have examined driver response to various rear-end collision avoidance systems (RECAS) display and algorithm alternatives, little research has been directed at creating a quantitative model of driver performance to evaluate these alternatives. Current considerations of driver behavior in developing warning algorithms tend to ignore the fundamental problem of driver inattention and assume a fixed driver reaction time with no further adjustment after the initial response. A more refined model of driver response to rear-end crash scenarios can identify more appropriate and timely information to be displayed to the driver. An attention-based rear-end collision avoidance model (ARCAM) is introduced that describes the driver’s attention distribution, information extraction and judgment process, and the reaction process. ARCAM predicts the closed-loop nature of collision response performance and explains how the driver might use RECAS warnings.
Value of Time in Freight Transport in Finland
Authors: Kurri Jari , Sirkiä Ari , Mikola Juha
Published: April 2007

In the socioeconomic evaluation of transportation investments affecting freight transport in Finland, no value of time is currently attributable to the freight itself. In order to estimate freight-specific values of time for road and rail transport, two separate studies using the same methodology were carried out. Stated preference technique—in which hypothetical choice situations between two road or rail transport alternatives were presented to transport managers in manufacturing companies in Finland—was used. Values of the attributes presented were based on the present transport in question. Level of service was characterized by three variables: transport time, transport cost, and reliability of the service (frequency and duration of unexpected delays). Personal interviews were carried out using a portable computer. The relative importance of the factors (i.e., values of transport time and delays) was derived from logit models. According to the survey, the average value of time for road transport for the selected commodity groups is about $1.5 per metric ton per hour, and the value of average delay is about $47 per metric ton per hour. For rail transport and different commodity groups, the average value of transport time is about $0.10, and the value of average delay is about $0.5 per metric ton per hour. These results stress the importance of the reliability of transport time. The values of transport time were considerably higher than those in the corresponding Swedish studies but lower than the values in several other studies.
Using Global Positioning System Data to Understand Variations in Path Choice
Authors: Jan Oliver , Horowitz Alan J. , Peng Zhong-Ren
Published: April 2007

A comprehensive set of Global Positioning System (GPS) vehicle location data from Lexington, Kentucky, households was analyzed to determine if such data can be helpful in improving path choice assumptions in traffic assignment models. The portion of the data used consisted primarily of a reconstruction of the street network and the lists of street segments in each path. Analysis was based on matches of trips (e.g., pairs of trips with similar origins and destinations). Matches were obtained for trips within households and for trips across households. Statistics used to compare trips in matches were a path deviation index and the percentage of identical links. It was found that the path chosen on a trip was quite sensitive to the location of the origin and destination and that the chosen path most often differed considerably from the shortest time path across the network. Paths for trips made by the same driver were very consistent over time; paths by different drivers showed more deviations even when the trip ends were the same or very similar. As a result of this research, recommendations are made as to how GPS data on path choice can be better collected in the future for improvement of traffic assignment models.
Bicriterion Traffic Equilibrium: T2 Model, Algorithm, and Software Overview
Authors: Dial Robert B.
Published: April 2007

T2 is a rational and rigorous bicriterion traffic assignment model developed around a stochastic linear generalized cost model, which forecasts path choices and consequent equilibrium link volumes of trip makers with diverse values of time. Its path choice criterion minimizes a disutility equaling a stochastic sum of two link attributes—usually time and cost— both of which may be flow dependent. In contrast with the classical traffic assignment model, T2 permits different travelers to respond differently (as a result of factors such as travel time, tolls, congestion, taste, etc.) to the same path choices. This research provides an overview of T2’s mathematical model, solution algorithm, and implementing software.
Traveler Responses to Advanced Traveler Information Systems for Shopping Trips: Interactive Survey Approach
Authors: Kraan Mariëtte , Mahmassani Hani S. , Huynh Nhan
Published: April 2007

This survey research describes an experiment that addresses travel decisions of trip makers for noncommuting trips. The survey considers recreational shopping trips for which trip makers can choose both destination and desired arrival time. An interactive stated preference instrument, the survey was designed and implemented for access and administration via the Internet. It was easily accessible and completely self-administered; participants could run the survey without the help of a project staff member. Data were also gathered automatically. Survey respondents were asked to make two shopping trips. They were provided with pretrip and en route traffic information for trips to shopping malls by predetermined routes. Respondents were asked their preferences concerning information items, factors affecting their mall choice, demographics, and familiarity with their residence and the shopping malls. The recruitment method by e-mail and the requirement to have Internet access led to a slightly biased sample—young males, many with higher education, were overrepresented in the sample. Results showed that respondents choose their shopping mall based on characteristics of the mall but that trip makers divert from their route when provided with delay information during their trip. It was found that about 25 percent of respondents even change their destination. Of the respondents who did not change their destination, nearly half chose to divert from their current route, whereas the other half stayed on the current route. Despite its current sample bias, the interactive Internet survey has proven to be a successful tool for gathering data on travel decisions. It is inexpensive, easy to administer, and provides reliable responses.
Promoting More Efficient Use of Urban Areas in Developing Countries: An Alternative
Authors: da Silva Lima Renato , Rodrigues da Silva Antônio Nélson , Yumiko Egami Cintia , Francisco Zerbini Luiz
Published: April 2007

Planners can apply a relatively simple and user-friendly tool to control the expansion of urban areas in developing countries. This tool, presented here, is based on a traditional accessibility index, which may be taken as a measure of urban development. The entire process of construction and analysis of the networks based on the accessibility index was carried out using a geographic information system for transportation (GIS-T). The tool has been tested in São Carlos, a medium-sized Brazilian city, in which the effects of some proposed real estate developments on the accessibility patterns have been studied. The results of this application show that the tool is suitable for selecting the best site for a new development among many alternatives, promoting more efficient use of the urban area.
Bus Accidents in India, Nepal, Tanzania, and Zimbabwe
Authors: Pearce T. , Maunder D.A.C. , Mbara T. C. , Babu D. M. , Rwebangira T.
Published: April 2007

Countries of the developing world are characterized by rapid urbanization, high growth rates of traffic and congestion, and decreasing regulation of public transport. Because the majority of the developing world’s inhabitants depend on public transport services for their mobility needs, safe, effective, and efficient public transport is essential to ensure adequate and affordable accessibility and the sustainable development of livelihoods in the rural and urban sectors. The operational environment of the public transport sector in Nepal, India, Tanzania, and Zimbabwe is examined, as well as the extent of accidents involving public transport vehicles and the likely causes. Finally, recommendations are made to reduce both the severity and the number of public transport accidents.
Control Strategies for Transit Priority
Authors: Skabardonis Alexander
Published: April 2007

Control strategies for transit priority have long been recognized as having the potential to improve traffic performance for transit vehicles, which could also lead to improved schedule reliability, reduced operating costs, and greater ridership. However, there have been relatively few successful implementations of transit priority measures on urban networks with signalized intersections in coordinated signal systems. Existing control strategies are reviewed, the major factors affecting transit priority are identified, and the formulation of both passive and active transit priority strategies for arterials with coordinated traffic signals are described. The proposed strategies were evaluated on a real-life arterial corridor. The proposed passive and active priority strategies placed major emphasis on the systemwide improvements to the transit movements and on minimization of the adverse impacts to the rest of the traffic stream. The criteria used to grant priority include the availability of spare green time in the system cycle length, progression at the downstream intersection(s), and schedule adherence. An evaluation technique was also developed to assist in the design of the signal priority strategies and to predict the impacts of the transit priority measures.
New Procedure for Detector Data Screening in Traffic Management Systems
Authors: Turochy Rod E. , Smith Brian L.
Published: April 2007

Automated monitoring of traffic conditions in traffic management systems is of increasing importance as the sizes and complexities of these systems expand. Accurate monitoring of traffic conditions is dependent on accurate input data, yet techniques that can be used to screen data and remove erroneous records are not used in many traffic management systems. Procedures that can be used to perform quality checks on the data before their use in traffic management applications play a critical role in ensuring the proper functioning of condition-monitoring methods such as incident detection algorithms. Tests that screen traffic data can be divided into two categories: threshold value tests and tests that apply basic traffic flow theory principles. Tests that use traffic flow theory use the inherent relationships among speed, volume, and occupancy to assess data validity. In particular, a test that derives the average effective vehicle length from the observed traffic variables detects a wide range of erroneous data. A new data-screening procedure combines both threshold value tests and traffic flow theory–based tests and can serve as a valuable tool in traffic management applications.
Maximum Possible Weaving Volume for Effective Operations of Ramp-Weave Areas: Online Estimation
Authors: Kwon Eil , Lau Rich , Aswegan James
Published: April 2007

Understanding the behavior of weaving flows and estimating the effects of time-variant traffic conditions on the capacity of weaving areas are of critical importance in developing effective operational strategies for freeway management. An online procedure for estimation of the maximum possible weaving volume over time for a given ramp-weave area is presented. The method is based on the findings from weaving behavior analysis, which indicates that under moderate to heavy flow conditions the diverging vehicles, that is, the freeway-to-ramp vehicles, tend to move to the auxiliary lane on entering the weaving area, whereas the ramp-to-freeway vehicles travel a short portion of the auxiliary lane before they merge to the main line. Therefore, the beginning portion of an auxiliary lane in a ramp-weave area is shared by both merging and diverging vehicles, and the length of such a shared area, called the effective weaving zone, varies depending on the length of a given weave section and the amount of weaving flow. Such join-then-split weaving behavior implies that the maximum value of the weaving volume in a ramp-weave area with one auxiliary lane is limited by the maximum through capacity of one lane. The proposed method reflects the weaving behavior described above and determines the maximum possible weaving volume for a given time interval as a function of exit and merge capacities, which are dependent on the traffic conditions downstream of weaving areas. Preliminary test results with 5 min of data from a ramp-weave site indicate that the maximum possible weaving volume is estimated with reasonable accuracy.
Distribution of Strains Within Hot-Mix Asphalt Binders: Applying Imaging and Finite-Element Techniques
Authors: Kose Sadi , Guler Murat , Bahia Hussain U. , Masad Eyad
Published: April 2007

Because of several orders of magnitude difference between the stiffness of aggregate and binder and the randomness of the binder domain boundaries, the induced deformation under loading can result in a wide distribution of stresses and strains within each of the components. It is expected that although aggregates undergo small strains, most of the strain will accumulate within the binder. Although studies have covered the micromechanics of hot-mix asphalt (HMA), information about the actual typical distribution of asphalt binder domains in HMA and the resulting distribution of stresses and strains is scarce. In this study, advances in imaging techniques are applied to understand the distribution of binder and air voids in selected HMAs. The objective is to determine the strain distribution within the binder using digitized images analyzed with finite-element procedures. This approach captures the image of the specimen cross section and converts the image into finite-element mesh after image processing. The images are converted to finite-element mesh and the finite-element program ABAQUS provides numerical solutions to relate bulk stresses or strains applied to the asphalt mixture to stresses and strains within the binder domains. The results are presented including a summary of the distribution of directional binder film thickness and maximum strains in the mastic domain. Also included is a discussion of the effect of air voids and mineral fillers.
Low-Temperature Fracture Testing of Asphalt Binders: Regular and Modified Systems
Authors: Hoare Todd R. , Hesp Simon A. M.
Published: April 2007

The results of low-temperature fracture testing of a large number of both regular and modified asphalt binders are discussed. Two Strategic Highway Research Program (SHRP) binders (Materials Reference Library Codes AAG-2 and AAN) were evaluated with 5 percent by weight of a variety of commonly used polymer modifiers. Specimens of three different sizes were tested in a three-point bend configuration, both with and without a notch. The original SHRP effort was aware of the need for a rigorous fracture mechanics-type binder test, but because of a lack of time and resources, only the bending beam rheometer and the direct tension test were ultimately developed. Some of the differences between failure strain and fracture toughness measurements are discussed, as well as how these differences may relate to pavement performance. The results of this study demonstrate that there is a large range of notch sensitivities and fracture energies for different polymer-modified binders, suggesting that the ductile-to-brittle transition (as measured with the direct tension test) may not be a totally reliable performance indicator. Fracture energy may be a better choice, since it combines the notched strength with a stiffness to yield a true material property that is independent of sample size and configuration.
New Class of Reactive Polymer Modifiers for Asphalt: Mitigation of Moisture Damage
Authors: Crossley Glen , Hesp Simon
Published: April 2007

A new class of reactive polymer modifiers designed to improve binder-aggregate adhesion in asphalt concrete was evaluated. Using a controlled free radical polymerization process, polyisoprene was prepared with short blocks of reactive amino- or silane-functional monomer at one end of the polymer chain. The reactive polymers so synthesized were tested with a modified version of the Tunnicliff-Root method (ASTM D4867) for measuring retained tensile strengths after water immersion moisture conditioning at 60°C for 24 h. It was found that the retained tensile strength of the unmodified samples was 53 percent, and the retained tensile strength of the regular polyisoprene-modified control samples was between 57 and 69 percent, depending on the polymer molecular weight and content. The best retained tensile strengths of 86 and 90 percent, respectively, were obtained with samples modified with 3 and 5 percent by weight of the higher-molecular-weight silane-functional polyisoprene. The method for obtaining the desired effect is flexible; lower-cost monomers, such as butadiene, and more common polymerization methods, such as emulsion or anionic polymerization techniques, may be used equally well to produce polymers with similar or better performance characteristics. An added benefit is that the tested polymers imparted significant improvements in low-temperature performance measured with the thermal stress restrained cooling test.
Fracture Energy Test for Highway Concrete: Determining the Effect of Coarse Aggregate on Crack Propagation Resistance
Authors: Jensen Elin A. , Hansen Will
Published: April 2007

Portland cement concrete fracture properties—specific fracture energy, fracture toughness, and brittleness—were investigated for typical Michigan highway concretes containing different coarse aggregates and varying in age: 7,28, and 91 days. These fracture properties can be determined from the complete load-deflection curve of a notched beam. The effective beam is 965 mm long, 100 mm wide, and 200 mm high, with a 100-mm center notch. Results show that the specific fracture energy, which determines the resistance to crack propagation, for a concrete pavement mix is controlled primarily by the coarse aggregate type. Differences of 100 percent were obtained between aggregate types. A glacial gravel yielded the highest resistance (160 N/m), and the dolomitic limestones and blast furnace slag yielded the lowest resistance (80–100 N/m), although the concretes all had similar strength properties. The fracture toughness, resistance to crack initiation, was found to be linear related with concrete strength. Typically this results in improved early age fracture toughness for concretes containing dolomitic limestone and blast furnace slag as coarse aggregate, compared to glacial gravel, because natural aggregate concrete typically has slower strength gain initially. Concrete brittleness, based on the entire load-deflection response, showed that concretes containing stronger coarse aggregate, such as glacial gravel, are significantly less brittle at early ages than are concretes containing weaker aggregate. However, these stronger aggregate concretes become more brittle, and thus crack sensitive, over time.
Temperature Gradient of Concrete Pavement Slab Overlaid with Asphalt Surface Course
Authors: Nishizawa Tatsuo , Shimeno Shigeru , Komatsubara Akinori , Koyanagawa Masashi
Published: April 2007

In the structural design of composite pavement with a concrete pavement slab overlaid with an asphalt surface course, it is very important to estimate the temperature gradient in the concrete slab. An asphalt surface course reduces the temperature gradient in an underlaid concrete slab, resulting in the reduction of thermal stress of the concrete slab. This effect was investigated by temperature measurement in model pavements and by thermal conductivity analysis. Thermal properties were estimated by a backanalysis by using measured temperatures over 1 year. From the numerical simulations varying the thickness of asphalt surface and concrete slab, the relationship between the reduction effect and the asphalt thickness was derived as a function of the thickness of asphalt surface course, which can be used in the structural design of the composite pavement.
Axisymmetric Finite Element Modeling of Block Pavement Subjected to Repeated Loading
Authors: Meng Chua Koon , Askree Zehra , Shackel Brian
Published: April 2007

A two-dimensional finite element code, PAVE2D, is used to model a concrete block pavement as a solid of revolution. However, use of this approach in its normal form poses a difficulty—the relatively stiff elements near the axis of revolution cannot rotate. It is proposed that the stiffness of these elements be modified to allow some degree of rotation that would still give a reasonable state of stress. This is done by determining a ratio of the modulus of a flat circular plate and that of a straight beam of equal span and thickness that would give an equal rotation along the entire span. This ratio is used to reduce the modulus of the elements representing the concrete blocks according to their proximity from the axis of revolution. PAVE2D is a large deformation capable code that has an updated Lagrangian formulation. The proposed method has an advantage over the traditional three-dimensional finite element analysis because it accommodates stress-related nonlinearity and geometric nonlinearity, and it is capable of simulating loading and unloading without huge computing resource requirements. The computer simulations shown include modeling a field test in which a 70-mm-thick block pavement was subjected to loading from a falling weight deflectometer and modeling block pavements 80 mm and 120 mm thick subjected to repeated loading. The proposed method can be used to evaluate different block shapes and arrangements and can be used to predict rutting characteristics of these pavements. The method applies to rigid pavement.
Incorporation of Reliability into Mechanistic-Empirical Pavement Design
Authors: Timm David H. , Newcomb David E. , Galambos Theodore V.
Published: April 2007

Pavement thickness design traditionally has been based on empiricism. However, mechanistic-empirical (M-E) design procedures are becoming more prevalent, and there is a current effort by AASHTO to establish a nationwide M-E standard design practice. Concurrently, an M-E design procedure for flexible pavements tailored to conditions within Minnesota has been developed and is being implemented. Regardless of the design procedure type, inherent variability associated with the design input parameters will produce variable pavement performance predictions. Consequently, for a complete design procedure, the input variability must be addressed. To account for input variability, reliability analysis was incorporated into the M-E design procedure for Minnesota. Monte Carlo simulation was chosen for reliability analysis and was incorporated into the computer pavement design tool, ROADENT. A sensitivity analysis was conducted by using ROADENT in conjunction with data collected from the Minnesota Road Research Project and the literature. The analysis demonstrated the interactions between the input parameters and showed that traffic weight variability exerts the largest influence on predicted performance variability. The sensitivity analysis also established a minimum number of Monte Carlo cycles for design (5,000) and characterized the predicted pavement performance distribution by an extreme value Type I function. Finally, design comparisons made between ROADENT, the 1993 AASHTO pavement design guide, and the existing Minnesota design methods showed that ROADENT produced comparable designs for rutting performance but was somewhat conservative for fatigue cracking.
Evaluation of Probability Distribution Function for the Life of Pavement Structures
Authors: Romanoschi Stefan A. , Metcalf John B.
Published: April 2007

Determination of the probability distribution function for the time to failure is essential for the development of pavement life models, because the probability distribution function reflects the variability in pavement degradation. The pavement life and failure time are associated with the number of equivalent standard axle load applications for which the degradations reach a critical level. When the critical degradation level is reached, maintenance and rehabilitation work needs to be done to improve pavement condition. Research was undertaken to identify the appropriate statistical models for determination of the probability distribution function for the time to failure of pavement structures. The study used the rutting data collected on a test lane at the first full-scale accelerated pavement test in Louisiana. The research indicated that closed-form solutions or Monte Carlo algorithms can be used when the degradation models have a known form. The bootstrap algorithm can be used to determine the confidence intervals for probability of failure at a given time. If the form of the degradation model is not known, the survival analysis method based on censored observations must be used. The methods can be used not only for rutting life models but also for other pavement life models: cracking initiation time, cracking life, roughness, and serviceability lives.
Load and Displacement Prediction for Shakedown Analysis of Layered Pavements
Authors: Shiau S. H. , Yu H. S.
Published: April 2007

A complete shakedown assessment of pavement behavior under repeated loading requires a shakedown load analysis as well as a displacement evaluation. Both load and displacement bounding calculations at shakedown are presented, and the pavement subjected to repeated loading is analyzed as a plane strain problem. The proposed shakedown load formulation is verified by using numerical results for a homogeneous isotropic half space. To illustrate the relevance of the numerical formulations, the numerically determined residual stresses are compared with available experimental data. The variation of shakedown loads with different material properties for two-layered pavements is investigated in detail. The results of permanent displacement bounds are presented and compared with the displacement finite element calculation. Simple design charts for the layered pavements are presented.
Mechanistic-Empirical Approach for Modeling Reflection Cracking
Authors: Eltahan Ahmed A. , Lytton Robert L.
Published: April 2007

Models developed to predict reflective cracking in flexible pavement overlays do not explicitly incorporate the combined effect of the cracked and uncracked areas in the original pavement. This affects the development of cracks in the overlay. Therefore, a model is needed that will incorporate this factor explicitly, making predicting of cracking in pavement overlays more realistic in pavement management systems and pavement reliability. A mechanistic approach based on fracture mechanics with an empirical stochastic form to develop the desired model is presented. This approach has been adopted because the new design trends (such as the new 2002 AASHTO design guide) will follow a more mechanistic approach than the current trends. In addition, this approach is lacking in the literature for data of in-service roads. The use of the developed model for the study of crack initiation is presented. Data obtained from the Florida Department of Transportation are divided into Interstates and arterials. The results show that the proposed model predicts the observed cracking with an R2 of 0.72 for the Interstates and 0.40 for the arterials. Because the exact time of crack initiation is not recorded, the observed crack-initiation time is approximated by the last time no cracking was observed (i.e., right before cracking was first recorded). The proposed methodology predicts the crack-initiation time with an average absolute error of 18.6 percent.