bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Simulation to Predict Safety and Operational Impacts of Increasing Traffic Signal Density
Authors: Drummond Kendall P. , Hoel Lester A. , Miller John S.
Published: April 2007

The use of simulation models to predict the safety and operational impacts of increased traffic signal density in suburban corridors is described. Using 10 years of data from two major arterials in Virginia, actual crash rates were compared with operational performance measures simulated by the Synchro/SimTraffic model. As expected, crash rates were positively correlated with stops and delay per main-line vehicle and negatively correlated with main-line speed. Three findings were significant. First, the correlation between crash rates and performance measures (main-line delay, speed, stops) was relatively strong despite the inherent variability in crash rates: R2 values ranged from .54 to .89. Second, three distinct regimes relate stops per vehicle to signal density: the installation of the first few signals causes a drastic increase in stops, the addition of the next set of signals causes a moderate increase in stops, and the addition of a third set of signals does not significantly affect the number of stops per vehicle. Third, multiple-regime models also relate total delay per vehicle to signal density. Two practical applications are suggested, one for safety and one for operations. To the extent that these measures correlate with crashes, simulation modeling may be used to estimate safety impacts of increased signals, which is appealing because simulation packages are becoming easier to apply. This safety-oriented endeavor was the primary motivation behind this research. A secondary, operational benefit, however, is that three regime models can suggest when, in the timeline of corridor development, the addition of a traffic signal is likely to degrade corridor performance significantly, thereby allowing decision makers to expend political capital when it is most beneficial.
Analysis of Severity of Young Driver Crashes: Sequential Binary Logistic Regression Modeling
Authors: Dissanayake Sunanda , Lu John
Published: April 2007

Young drivers have the highest fatality involvement rates of any driver age group within the United States driving population. They also experience a higher percentage of single-vehicle crashes compared with others. When looking at the methods of improving this alarming death rate of young drivers, it is important to identify the determinants of higher crash and injury severity. With that intention, the study developed, using the Florida Traffic Crash Database, a set of sequential binary logistic regression models to predict the crash severity outcome of single-vehicle fixed-object crashes involving young drivers. Models were organized from the lowest severity level to the highest and vice versa to examine the reliability of the selection process, but it was found that there was no considerable impact based on this selection. The developed models were validated and the accuracy was tested by using crash data that were not utilized in the model development, and the results were found to be satisfactory. Factors influential in making a crash severity difference to young drivers were then identified through the models. Factors such as influence of alcohol or drugs, ejection in the crash, point of impact, rural crash locations, existence of curve or grade at the crash location, and speed of the vehicle significantly increased the probability of having a more severe crash. Restraint device usage and being a male clearly reduced the tendency of high severity, and some other variables, such as weather condition, residence location, and physical condition, were not important at all.
Estimating Safety by the Empirical Bayes Method: A Tutorial
Authors: Hauer Ezra , Harwood Douglas W. , Council Forrest M. , Griffith Michael S.
Published: April 2007

The empirical Bayes (EB) method addresses two problems of safety estimation: it increases the precision of estimates beyond what is possible when one is limited to the use of a 2- to 3-year accident history, and it corrects for the regression-to-mean bias. The increase in precision is important when the usual estimate is too imprecise to be useful. The elimination of the regression-to-mean bias is important whenever the accident history of the entity is in some way connected with the reason why its safety is estimated. The theory of the EB method is well developed. It is now used in the Interactive Highway Safety Design Model and will be used in the Comprehensive Highway Safety Improvement Model. The time has come for the EB method to be the standard and staple of professional practice. The study’s goal is to facilitate the transition from theory into practice.
Modeling the Simultaneity in Injury Causation in Multivehicle Collisions
Authors: Ouyang Yanfeng , Shankar Venky , Yamamoto Toshiyuki
Published: April 2007

Constrained by the single-equation specification, traditional logit or probit models for traffic accident severities can only model one severity at a time. Single-equation models fail to account for the simultaneity of injury severity outcomes in multivehicle collisions. An attempt to account for this simultaneity is made by presenting a simultaneous logit model of endogenous interrelationships among injury severities in multivehicle collisions. Car-truck collision data in Washington State between 1990 and 1996 are used for a simultaneous binary logit model to determine the effects of various exogenous factors in the presence of injury simultaneity, and empirical comparisons with traditional single-equation logit models are also provided. The methodology presented provides for significant efficiency gain when correlation between injury severities is high and can easily be extended to multiple severity categories in multiple-vehicle collisions. Empirically, it is also found that parameter estimates for key roadway design variables may vary greatly between a simultaneous logit and its single-equation counterparts. Another finding from this methodology is that preventive measures for head-on collisions, or enforcement of drunk-driving regulations among truck drivers, as well as limiting the occurrence of high-speed curve designs on truck routes, appear to be the most likely factors for significant potential savings in social costs from car-truck collisions.
Identifying Locations with Potential for Accident Reductions: Use of Direct Diagnostics and Pattern Recognition Methodologies
Authors: Kononov Jake
Published: April 2007

Safety performance functions reflect the complex relationship between exposure, usually measured in annual average daily traffic, and accident count for a unit of road section over a unit of time. One of the main uses of the safety performance functions is to identify locations that experience more accidents than expected, thus exhibiting a potential for accident reduction. Overrepresentation in the number of accidents above the expected or normal threshold predicted by the safety performance function is only one of many indicators of a potential for accident reduction. Accident type, severity, road condition, spatial distribution of accidents, and lighting conditions are only a few of the many important symptoms of the accident problem. Two methodologies are introduced for identification of locations with potential for accident reduction: direct diagnostics and continuous pattern recognition analysis. Use of these methodologies revealed that existence of accident patterns susceptible to correction may or may not be accompanied by the overrepresentation in accident frequency detected by the safety performance functions.
Amperage and Treatment Time Monitoring to Evaluate Stone Column Effectiveness
Authors: Rollins Kyle M. , Giles Eric
Published: April 2007

During stone column installation for the seismic retrofit of the Mormon Island Auxiliary Dam, several important parameters of the construction process were continuously monitored using a data acquisition system. This system provided data on operating amperage, stone volume, and treatment time as a function of probe depth. In this study, treatment time and amperage values were analyzed in detail. In addition, equations combining amperage and time were developed to define the amount of energy applied to the soil during remediation. Applied energy, as measured by treatment time and amperage, was then compared to (N1)60 values from Becker penetration tests. This test was selected as the evaluation tool because of the presence of gravel and cobbles. Analysis of the data suggests that the maximum amperage at a given depth can be used to separate layers with high and low fines contents. In general, the maximum amperage was more a function of soil type than of treatment time. For soils with high fines content, the maximum amperage was consistently low relative to soils with low fines content and did not increase significantly with continued vibration. Comparisons between the applied energy and the posttreatment Becker penetration tests results showed that slight improvement is possible in soils with higher fines contents. However, increasing the vibration time in these soils did not increase the (N1)60 values. Therefore, additional time beyond that required to install the column was not useful. For soils with low fines contents, the posttreatment (N1)60 value did tend to increase with additional applied vibration energy, but the scatter in the results was substantial.
Field Evaluation of Construction Alternatives for Roadways over Soft Subgrade
Authors: Edil Tuncer B. , Benson Craig H. , Bin-Shafique M. , Tanyu Burak F. , Kim Woon-Hyung , Senol Aykut
Published: April 2007

Alternative methods for providing a stable platform over soft subgrades were evaluated using a 1.4-km section along a Wisconsin State highway that incorporated 12 test sections to evaluate 9 different stabilization alternatives. A variety of industrial by-products and geosynthetics were evaluated for stabilization. The industrial by-products included foundry slag, foundry sand, bottom ash, and fly ash as subbase layer materials. The geosynthetics included geocells, a nonwoven geotextile, a woven geotextile, a drainage geocomposite, and a geogrid. The same pavement structure was used for all test sections except for the subbase layer, which varied depending on the properties of the alternative material being used. All test sections were designed to have approximately the same structural number as the conventional pavement structure used for the highway, which included a subbase of granular excavated rock. Observations made during and after construction indicated that all sections provided adequate support for the construction equipment and no distress was evident in any part of the highway. Each of the alternative stabilization methods, except a subbase prepared with foundry sand, appear to provide equivalent or greater stiffness than that provided by control sections constructed with excavated rock. However, the foundry sand subbase is providing adequate support. Analysis of leachate collected from the base of the test sections shows that the by-products discharge contaminants of concern at very low concentrations.
Linking New Hampshire’s Rock Cut Management System with a Geographic Information System
Authors: Fish Marc , Lane Richard
Published: April 2007

The New Hampshire Department of Transportation (NHDOT) first conducted a Rock Cut Hazard Survey in 1975, which included 182 rock cuts. The program has evolved since 1975 and now incorporates 380 rock cuts and 4 Rock Fall Hazard Rating Systems. Using New Hampshire’s State Planning and Research funding, a research project was initiated with the objective of combining new rock cut data with preexisting data into a geographic information system (GIS). Rock cut point features were collected for every rock cut with the Global Positioning System and were added as a data layer on top of existing data coverage available through the department’s GIS server. A relational database was developed that would store all rock cut data and would be linked to the GIS through a standard language query connect statement. A Brunton compass was used to collect rock cut structural data, and a digital camera was used to photograph every rock cut. The structural data were graphically represented in the GIS in the form of rose diagrams, stereonets, and density plots. A laser profiler was used to collect two-dimensional profiles on selected rock cuts so rock fall simulations could be conducted. The GIS does have limitations, including the network bandwidth, accessibility restrictions, and resource allocation for maintaining current and accurate data. Deployment of an Internet mapping service has been recommended to increase accessibility and to allow all NHDOT users access to the Rock Cut Management System through a web browser.
Quantitative Risk Assessment for Landslides
Authors: Roberds William J. , Ho Ken K. S. , Leroi Eric
Published: April 2007

Landslides are a serious problem in many parts of the world; they cause public casualties, property damage, and loss of service, and they cost significant resources to prevent and mitigate. Traditional approaches to landslide issues generally work well, but they only implicitly consider the significant uncertainties and consequences involved. An integrated risk assessment and risk management approach corrects this limitation. Quantitative risk assessment (QRA) is an established methodology that provides input for practical risk management of landslide issues and supplements traditional approaches. QRA provides a framework for anticipating and definitively evaluating potential slope-related problems so they can be accepted or cost-effectively mitigated and the residual risks can be communicated. In QRA, the potential slope-related problems (i.e., various types and sizes of landslides) are evaluated with respect to their probability (over a particular period) or frequency of occurrence and their consequences (e.g., public casualties) if they do occur. QRA can be done correctly in various ways, with the best way depending on the specific application, ranging from global issues for developing program policy to site-specific issues for detailed slope design. However, users skilled in geotechnical engineering and risk assessment are needed to perform QRA correctly and cost-effectively and to understand the limitations of the results. Perceived limitations of QRA include accuracy issues, acceptability issues (e.g., by regulators), and aversion issues (e.g., liability). However, many of these issues are easily resolved and are not real limitations, so that QRA, although not perfect, is advantageous in many cases.
Prefabricated Vertical Drains for Use in Soil Vapor Extraction Applications
Authors: Collazos O. M. , Bowders J. J , Bouazza M.
Published: April 2007

Soil vapor extraction (SVE) is an effective and cost-efficient method of removing volatile organic compounds and petroleum hydrocarbons from unsaturated soils. However, SVE becomes ineffective in soils with low permeability—for example, soils with air permeabilities less than 1 Darcy. Prefabricated vertical drains (PV drains) have been used to dewater finegrained soils for more than 20 years. For the last 5 years, PV drains have been used for soil flushing applications to remove contaminants below the groundwater table. Incorporating PV drains in an SVE system can extend the effectiveness of SVE to lower permeability soils by shortening the airflow paths and ultimately expediting contaminant removal. An advantage of using PV drains in place of conventional SVE wells is that they can be installed relatively inexpensively. The objective is to effectively incorporate PV drains into an SVE remediation system and to demonstrate a PV drain-enhanced SVE system at full scale.
Solute Effects on Long-Duration Frost Heave Behavior of Limestone Aggregate
Authors: Guthrie W. , Zhan Hongbin
Published: April 2007

The performance of pavements in cold climates greatly depends on the frost susceptibility of the base and subgrade layers. Frost heave caused by ice lensing within the pavement structure can create distresses in the surface that lead to cracking and poor ride quality. Furthermore, thawing during a warm period can cause a supersaturated condition in the roadbed that dramatically reduces soil strength and increases vulnerability to damage under trafficking. A laboratory study was performed at the Texas Transportation Institute to assess the long-duration frost heave behavior of a limestone aggregate base material. The computer program ICE2, which tracks heat, water, and solute flow during the freezing process, demonstrates the important role of salt content in the ice lensing mechanism. The program successfully models a two-stage frost heave behavior observed in the laboratory and affords an explanation of the frost heave events in a step-by-step fashion. Accurate frost heave modeling must account for changes in solute concentrations during the freezing process.
Perspective on Our National Air Transportation System: Past, Present, and Future
Authors: McKelvey Francis X.
Published: April 2007

This presentation contains a discussion of the reconfiguration of the route structure and growth of the U.S. air transportation system from 1970 to 2000. It highlights the evolution and importance of the regional airline industry in providing feeder service to hub airports and service to small- and medium-sized communities. It discusses the expected growth of the demand for air transportation during the period 2001 to 2011. It reviews the situation with respect to airport delay and the factors contributing to these delays and discusses the impact of both demand and capacity changes on airport delay. It contains an indication of recent initiatives to address airport terminal planning issues related to level of service. Finally, it presents a review of aviation security and the implications of the events of September 11 on the airlines and passengers.
Airport Terminal Signs: Use of Advance Guide Signs to Speed Search Times
Authors: Kichhanagari Reddy , Motley Rosa DeRamus , Duffy Susan A. , Fisher Donald L.
Published: April 2007

Airports are becoming increasingly busy. Congestion along the roadways to and from airports is increasing correspondingly. In this context, airport ground signage plays an especially critical role in driver satisfaction and safety. Perhaps most essential is the signage that tells drivers the terminal at which their airline either departs or arrives. Airlines leaving from a given terminal are typically listed as a group on a single terminal sign. In the not-so-distant past, the number of airlines was relatively small. Drivers could easily scan the list of airlines on a terminal sign in a few seconds. However, the number of airlines leaving from many airports has dramatically increased in the last 25 years. Thus, the number of airlines listed on a given terminal sign has had to increase as well. At some airports, there can be as many as 20 airline names on a terminal sign. This makes searching for a particular airline difficult without multiple, short glances. In some cases, drivers simply do not have enough time to scan the entire terminal sign. This creates driver frustration and, perhaps indirectly, leads to incidents. In other cases, drivers can spend much longer than they should with their eyes on the terminal sign and not on the road. This creates potential safety problems. The effectiveness is evaluated of an advance information sign that can reduce the search time by as much as 50 percent, both when the target airline is present and when it is absent on a given terminal sign. Applications to other signage are discussed.
Effect of T-TMA on Capacity and Delay at Los Angeles International Airport
Authors: Hansen Mark , Mukherjee Avijit , Knorr Dave , Howell Dan
Published: April 2007

Free Flight Phase 1 (FFP1) is an FAA program for improving the performance of the National Airspace System (NAS) through the deployment of advanced technologies for air traffic management. In addition to the deployment activities, FFP1 includes a significant evaluation component, which faces a significant hurdle. A plethora of factors—weather, demand, enhancements to the NAS infrastructure not related to FFP1, facility outages, and so on—may also cause changes in NAS performance. It is necessary to normalize for these factors in order to determine the effect of FFP1. Normalization procedures to isolate the impact of the implementation of an FFP1 technology—the Terminal Area Traffic Management Advisor (T-TMA)—are documented at the Southern California TRACON, where it is used for controlling traffic into Los Angeles International Airport. Two examples of normalization are presented. One examines the effect of T-TMA on airport arrival capacity, and the other looks at arrival delay. The results, although preliminary given the short time since implementation, are consistent: it appears that capacities have increased and delays decreased as a result of the deployment of the tool. Moreover, the magnitudes of the delay reductions and capacity increases are consistent.
Analysis of Factors Affecting Occurrence and Severity of Air Traffic Control Operational Errors
Authors: Gosling Geoffrey
Published: April 2007

The rate of occurrence of air traffic control operational errors is recognized as an important measure of the safety performance of the National Airspace System. As the volume of air traffic increases and new automated air traffic control decision support tools are introduced, there is a concern not only to increase the level of safety in the system by reducing the occurrence of operational errors but also to ensure that efforts to increase the capacity of the system do not adversely affect safety. Recent trends in air traffic control operational errors in the United States are analyzed. Factors that have been found to influence the rate of occurrence of these errors are discussed, and the relationship between the severity of operational errors in an en route environment and the traffic characteristics at the time are examined. The limitations of the information currently available to support the analysis of operational errors are described. Finally, the data requirements are addressed for future research to better understand the causal factors affecting the rate of occurrence of operational errors and to develop strategies to enhance the safety of the National Airspace System.
Modeling the Economic Impact of Adverse Weather into En Route Flights
Authors: Quan Chuanwen , Trani Antonio A. , Srinivas Sale
Published: April 2007

A methodology is presented to quantify and minimize the effect of adverse weather on commercial and general aviation traffic. The method described uses two simple models, the Air Traffic Flow Model and the Adverse Weather Impact Model, to quantify the impact of adverse weather into regional airspace operations in the National Airspace System (NAS). The impact of adverse weather in aviation in system delays is well documented. Weather is a major source of delays in NAS. In the past 5 years, weather has accounted for 71.2% of all delays in NAS according to statistics compiled and published by the FAA. Adverse weather varies in extent from a few square miles to thousands of square miles. Besides causing delays, it affects the safety, comfort, and efficiency of aviation. Better models to manage air traffic under adverse weather conditions are needed. Ultimately, these models could be deployed as decision-support systems to aid air traffic personnel to divert traffic optimally in a real-time scenario.
International Survey of Performance Measurement in Airports
Authors: Francis Graham , Fry Jackie , Humphreys Ian
Published: April 2007

The seemingly relentless growth in air traffic and the introduction of commercial and private models of airport ownership have changed the scope and significance of performance measurement for airport management, regulators, and stakeholders. The findings of a questionnaire survey are reported. The survey examined the nature and prevalence of the performance measurement of airports. Previous studies have examined specific airports or groups of airports and compared performance. This research assesses the way in which performance measures are used by management at the world’s busiest passenger airports using empirical evidence collected principally through the means of a worldwide questionnaire survey of the 200 largest passenger airports. A rich picture of various performance measurement practices was discovered.
Small Aircraft Transportation Systems: Effects on Accessibility to Commercial Air Transportation for Florida’s Suburban and Rural Population
Authors: Young Seth
Published: April 2007

One of the primary goals of the Small Aircraft Transportation System (SATS) program sponsored by the National Aeronautics and Space Administration is to “create access to more communities in less time.” The program targets to improve accessibility to commercial air transportation to underserved suburban and rural communities. By implementing the latest technology communications and navigation systems at strategically located general aviation and light commercial airports, SATS hopes to bring enhanced levels of accessibility to these markets. Results are presented of a study conducted to identify the regions within the state of Florida where the implementation of SATS technology would be most beneficial in terms of providing accessible commercial air service to currently underserved suburban and rural communities. The study considers the current use of public-use airports within the state and correlates the availability of commercial air service to the state’s population density and transportation infrastructure characteristics to estimate the percentage of the state’s population that lives within “tolerably accessible” 30-min travel times to the airports that provide such service. It was found that less than 70% of Florida’s population lives within a 30-min drive of a commercial service airport. Several airports within the state are identified where, if commercial service capabilities were provided through SATS technology, accessibility to air transportation would increase to 95% of the population. The results of this study are currently being applied as part of a program led by the Southeast SATS Lab consortium to bring SATS to Florida and the southeastern United States.
Restricting Use of Reverse Thrust as an Emissions Reduction Strategy
Authors: Rice Colin
Published: April 2007

As more metropolitan areas approach “nonattainment” status for ozone, air pollution at airports is becoming an increasingly important topic. Most proposed emissions reduction strategies target passenger automobiles and airport ground service equipment (GSE). At many airports, the future growth in oxides of nitrogen (NOx) emissions from aircraft is likely to offset any reduction achieved from GSE or passenger vehicles. In some metropolitan areas, airports may be responsible for as much as 10% of the regional NOx. As a result, other alternatives are needed for emissions reduction at airports. Reverse thrust is commonly used along with wheel brakes to slow aircraft during landing and to “power back” aircraft away from a boarding gate. Currently, air pollution emissions generated during reverse thrust are not included in airport emissions inventories. Because the majority of aircraft NO, emissions occur off-airport during climb out and approach, reverse thrust can be responsible for an additional 15% or more of the on-airport NO,. Because this additional NOx is emitted over a relatively small area, it can create significant air quality impacts in the vicinity of the busiest airports. An attempt is made to quantify the air quality effect of NOx emissions produced during reverse thrust, using Dallas-Fort Worth International Airport as a case study. The significance of the airport’s emissions from a regional standpoint and state implementation plan photochemical grid modeling are addressed.
Development of Deterioration Prediction Models for Airfield Rigid Pavements
Authors: Suh Young-Chan , Park Dong-Yeob , Jeong Kyoung-Young
Published: April 2007

Predicting deterioration in airfield pavements is extremely important to maximize the benefits of pavement management. An accurate prediction of pavement deterioration helps the decision maker to determine the planning and cost allocation of maintenance and rehabilitation more effectively. Mathematical prediction models for the deterioration of rigid airfield pavements in South Korea were developed. To derive the models, an integrated database of pavement conditions, age, traffic volume, and other characteristics was assembled. A total of 847 sample units from six airports, from 6 to 40 years old, was used for the development and validation of the models. Four pavement deterioration prediction models were developed for unmaintained and maintained sites with respect to runways and taxiways. From the validation plots, the pavement condition indexes (PCIs) predicted were in good agreement with the measured PCIs. Results from the independent data demonstrated an acceptable degree of accuracy of the models. It was also found that there was no significant difference between low-speed sections (start and end of a runway) and high-speed sections (center portion of a runway).
Louisiana Experience with Crumb Rubber-Modified Hot-Mix Asphalt Pavement
Authors: Huang Baoshan , Mohammad Louay N. , Graves Philip S. , Abadie Chris
Published: April 2007

A comparative study of laboratory and field performance of several applications of crumb rubber-modified (CRM) hot-mix asphalt in Louisiana is presented. Eight CRM asphalt pavement sections were constructed by eight different CRM processes or applications. These eight CRM sections were built at five state highway projects. A control section with conventional asphalt mixture was constructed at each project to compare with the performance of pavement sections built with CRM asphalt mixtures. To evaluate the mixture characteristics of the CRM and conventional mixes, laboratory tests of Marshall stability and flow, indirect tensile strength and strain, and indirect tensile resilient modulus were conducted on field compacted Marshall specimens. Comparisons of the field performances of the pavements were achieved through roadway core air void analysis, rut-depth measurement, international roughness index, pavement structure numbers measured through the Dynaflect (dynamic deflection determination) system, and visual inspections of cracks. The results indicated that the conventional mixtures exhibited higher laboratory strength characteristics than the CRM mixtures. The pavement sections constructed with CRM asphalt mixtures showed overall better performance indices (rut depth, fatigue cracks, and international roughness index numbers) than the corresponding control sections after 5 to 7 years of traffic.
Evaluation of Measurement Techniques for Asphalt Pavement Density and Permeability
Authors: Prowell Brian D. , Dudley Michael C.
Published: April 2007

A pavement quality indicator device developed through an NCHRP project, the Corelok device, and laboratory and field permeability index devices were evaluated for their potential to improve the Virginia Department of Transportation’s density specification or to be designated for use in a replacement specification. Fifteen samples were taken from six projects representing three nominal maximum aggregate sizes. Densities measured by a nuclear gauge correlated well with core densities measured in accordance with AASHTO T166 and by the Corelok device. Pavement quality indicator readings appeared to be repeatable but did not correlate with the densities measured in accordance with AASHTO T166 or with the Corelok device. A fair correlation was obtained for two projects. Laboratory permeability and field permeability indices were correlated with pavement density. A good correlation was found between the laboratory permeability and field permeability indices. The relationship appears to be linear in the range agencies typically specify.
Influence of Asphalt Tack Coat Materials on Interface Shear Strength
Authors: Mohammad Louay N. , Raqib M. , Huang Baoshan
Published: April 2007

Asphalt tack coat is a light application of asphalt, usually asphalt diluted with water. It is used to ensure a bond between the surface being paved and the overlying course. Normally, hot asphalt cements, emulsified asphalts, or cutback asphalts are used as tack coats. The objective of this study was to evaluate the practice of using tack coats through controlled laboratory simple shear tests and determine the optimum application rate. The influence of tack coat types, application rates, and test temperatures on the interface shear strength was examined. Four emulsions (CRS 2P, SS-1, CSS-1, and SS-1h) and two asphalt binders (PG 64-22 and PG 76-22M) were selected as tack coat materials. The residual application rates considered were 0.00 (0.00), 0.09 (0.02), 0.23 (0.05), 0.45 (0.1), and 0.9 (0.2) L/m2 (gal/yd2). A simple shear test was performed to determine the shear strength at the interface at two test temperatures, 25°C (77°F) and 55°C (131°F). The results indicated that CRS-2P emulsion was the best tack coat type and 0.09 L/m2 (0.02 gal/yd2) was the optimum application rate at which a maximum interface shear strength was measured for both test temperatures.
Simple Performance Test for Fatigue Cracking and Validation with WesTrack Mixtures
Authors: Wen Haifang , Kim Y.
Published: April 2007

Viscoelastic characterization of asphalt concrete in indirect tensile (IDT) testing and development of a simple performance test for fatigue cracking are described. A 50-mm gauge length was adopted to measure the horizontal and vertical deformations with surface-mounted linear variable differential transducers on an IDT specimen with a 100- or 150-mm diameter and 38-mm thickness. The effect of a concentrated load under loading strips on vertical displacement within the 50-mm gauge length was evaluated by the digital image correlation method, a noncontact, full-field displacement and strain measurement technique. The theory of viscoelasticity was used to develop analytical solutions for creep compliance and center strain from displacements measured on the specimen surface. These solutions were verified by three-dimensional finite element viscoelastic analysis. IDT creep and strength tests were performed on fine and coarse mixtures from WesTrack with various asphalt contents and air void contents, and various parameters determined from the analysis of these data were compared with the known fatigue performance of these mixtures from the WesTrack testing facility. The fracture energy obtained from viscoelastic analysis of the IDT strength test at 20°C correlated highly with the field performance of these mixtures at WesTrack.
Evaluation of Fatigue Healing Effect of Asphalt Concrete by Pseudostiffness
Authors: Si Zhiming Si , Little Dallas N. , Lytton Robert L.
Published: April 2007

The pseudostrain concept based on the extended nonlinear elastic—viscoelastic correspondence principle has been demonstrated in this research to be an appropriate and efficient method for evaluating microdamage and healing during the fatigue damage process. Pseudostiffness can be used to monitor microdamage and healing during the fatigue test. Pseudostiffness decreases consistently with an increasing number of loading cycles, which indicates that the microdamage occurs during the fatigue test. The significant recovery of pseudostiffness after rest periods indicates that there is a strong healing due to rest periods. The effects of hydrated lime on fatigue microdamage and healing have also been evaluated based on pseudostiffness recovery. The impact of healing during rest periods is evident and substantial. The degree of healing is mixture dependent. The ability of a mixture to heal is largely related to binder properties. Adding hydrated lime to the mixtures tested generally improved the healing potential of the mixtures. In general, stiffer mixtures have better healing and longer rest periods result in greater healing. The mechanism of healing is evaluated by two theories. The initial healing rate is governed by nonpolar surface energy, and the final healing rate is governed by polar surface energy.
Use of Stiffness of Hot-Mix Asphalt as a Simple Performance Test
Authors: Pellinen Terhi K. , Witczak Matthew W.
Published: April 2007

The objective was to determine whether the stiffness of a mix could be used as a simple performance test (SPT) parameter to complement the Superpave® volumetric mix design. This was investigated by a statistical analysis of the strength of the correlation between different mixture stiffness parameters and field performance (rutting, thermal, and fatigue cracking). A total of 30 mixtures were tested with laboratory-fabricated specimens. The studied stiffness parameters were compressive dynamic (complex) modulus | E*|, simple shear tester (SST) shear (complex) modulus | G*|, and dynamic elastic modulus Ed, obtained from ultrasonic wave propagation. Also, computed stiffness factors | E*|/sin ϕ and | G*|/sin ϕ for rutting and | E*|sin ϕ for cracking were studied as analogous to the Superpave binder specification. Research indicated that the correlation to rutting varied based on test temperature and frequency; it peaked at 54.4°C and 5 Hz. At peak conditions, | E*|/sin ϕ had better statistical correlation to rutting than | E*|, but correlations reversed at lower frequencies. Although | E*| and | G*| had similar correlation to rutting, analysis of test data indicated that the SST shear testing gave lower stiffness values and higher phase-angle values than the compressive dynamic modulus testing, even when Poisson’s ratio effects were considered. This was especially true at high temperatures. Because of these and other reasons, the dynamic modulus | E*| was recommended as the SPT parameter for rutting as well as for fatigue cracking. None of the studied parameters turned out to be adequate performance indicators for thermal cracking.
Effect of Aggregate Structure on Rutting Potential of Dense-Graded Asphalt Mixtures
Authors: Nukunya Bensa , Roque Reynaldo , Tia Mang , Mehta Yusuf A.
Published: April 2007

Superpave® mix design, as the name suggests, was developed to provide superior-performing pavements for the transportation industry. However, researchers and designers in their quest to provide such mixtures have encountered problems with some design specifications, such as the restricted zone. Superpave recommends that designers avoid grading through the restricted zone to eliminate tender mixes and gradations that may be too close to the maximum density line. But studies of the performance of the restricted zone have indicated that dense-graded mixtures that violate this requirement have provided good performance. It has also been reported that mixtures that are graded below the restricted zone (BRZ) have poorer rutting performance than those that are graded above the restricted zone (ARZ) or through the restricted zone. It is also known that the minimum voids in mineral aggregates (VMA) requirement, which was established to ensure durability, is very difficult to achieve. It also leads to overasphalting in BRZ mixtures and compromises their resistance to rutting. The effect of aggregate structures on rutting performance of mixtures is examined. Seven limestone and three granite mixtures were used. Six were BRZ mixtures and four were ARZ mixtures. After the behavior of the mixtures was investigated, it was concluded that BRZ mixtures developed different aggregate structures than ARZ mixtures and that the performance of mixtures depended on their aggregate structures. It was observed that the high VMA requirement caused overasphalting in BRZ mixtures, hence their dismal rutting performance compared with ARZ mixtures.
Shear Properties as Viable Measures for Characterization of Permanent Deformation of Asphalt Concrete Mixtures
Authors: Goodman Stephen N. , Hassan Yasser , El Halim Abd El Halim
Published: April 2007

Released in 1994, the Superpave® asphalt mix design system represented the culmination of a $50 million investment by the Strategic Highway Research Program to reduce the overall life-cycle costs of asphalt pavements. At this time, an extensive investigation to recommend a laboratorybased simple performance test for evaluating the resistance of Superpave mixes to permanent deformation is under way through the NCHRP. As a complementary effort, researchers at Carleton University are developing a field simple performance test for asphalt mixes known as the in situ shear stiffness test (InSiSST). InSiSST is unique to the asphalt industry; it measures the shear properties of compacted asphalt layers in the field without the need for coring or specimen preparation. Initial test results at the Superpave specific pavement studies test site (SPS-9) in Petawawa, Ontario, have shown excellent correlation between the in situ shear stiffness and observed permanent deformation. With additional testing and correlation, it is hoped that the InSiSST facility will complement the laboratory Superpave simple performance test to provide the asphalt industry with improved tools for mitigating permanent deformation. Information about the development effort is presented for context purposes, but the main objective is to further establish the benefit of fundamental asphalt shear properties for characterizing resistance to permanent deformation by presenting new and powerful performance models relating asphalt mix properties and shear properties to permanent deformation.
Standardized Procedure for Analysis of Dynamic Modulus |E*| Data to Predict Asphalt Pavement Distresses
Authors: Shenoy Aroon , Romero Pedro
Published: April 2007

A standardized procedure is presented by which various asphalt concrete mixtures can be compared and their expected performance can be assessed in a uniform manner with the simple performance test suggested by NCHRP 9-19: Superpave Support and Performance Models Management. The frequency sweep data generated from the test are available in terms of dynamic modulus | E*| versus frequency at the measurement temperature under different levels of confining stress [0, 20, 30 psi (0, 0.14, 0.21 MPa)]. The moduli versus frequency data at different temperatures are unified to form a single curve for each mixture through a normalizing parameter. The temperature at which the normalizing parameter becomes equal to 1 is designated the specification parameter T s (°C) for assessing mixture performance. Each unified curve is fitted with a constitutive equation from which model parameters are evaluated. Slope B1 in the low-frequency region of the unified curve, when normalized with the term ( T/ T s), results in a parameter that is related to asphalt pavement distress at high temperature T. It is shown that B1/ T s is related to rut depths measured at different WesTrack (a full-scale test track) sections and the correlation improves with increasing confining stress. There is a good possibility that slope B2 in the high-frequency region of the unified curve may relate to distresses in the intermediate temperature range, such as fatigue cracking. A preliminary check shows this may be true, but data are too limited to draw firm conclusions.
Dynamic Modulus of Asphalt Concrete with a Hollow Cylinder Tensile Tester
Authors: Buttlar William G. , Bauer Jason M. , Sherman Daniel S.
Published: April 2007

A hollow cylinder tensile tester (HCT) has recently been shown to be a suitable surrogate test device for the Superpave® indirect tension test. The feasibility of using the HCT to obtain the dynamic modulus of asphalt concrete was explored. Previous studies have shown the dynamic modulus of asphalt concrete in tension and compression to be similar at low temperatures and high loading frequencies and that minor differences can be expected at higher temperatures and lower loading frequencies. Here, the HCT device compared favorably with dynamic modulus measurements obtained with uniaxial compression testing apparatus at 0°C and 20°C. In addition, test results were found to be in reasonable agreement with the Witczak dynamic modulus predictive equation. The ability to simply and rapidly measure the creep compliance, tensile strength, and dynamic modulus of bituminous paving mixtures over a range of temperatures and loading conditions makes the HCT device a useful general-purpose mixture analysis tool. It appears that this portable device may serve as a practical method to satisfy testing requirements for high reliability (Level 1) pavement designs in the forthcoming AASHTO 2002 design guide being developed under NCHRP 1-37A for the mitigation of both fatigue cracking and thermal cracking. However, a broader experimental program, including tests at higher temperatures and a broader range of test frequencies, is needed to fully validate the compatibility of HCT measurements with NCHRP 1-37A models.
Impact of Information and Communication Technologies on Logistics and Freight Transportation: Example of Vendor-Managed Inventories
Authors: Rabah Mouhamad , Mahmassani Hani S.
Published: April 2007

A framework to assess the impacts of information and communication technologies (ICTs) on supply-chain and logistics operations, including the movement of freight, is presented. The framework reflects transformation of the traditional supply chain into a virtually forged one and its link to the transportation sector. To illustrate and quantify cost savings that might result from information sharing among supply-chain participants, the example of a vendor-managed-inventory (VMI) strategy in a two-echelon distribution channel is considered. Models of operation with and without VMI are developed; the results of applying the two strategies to the same demand-stream characteristics allow assessment of the impact of ICT-enabled VMI logistics strategy. Reductions in total cost are achieved across all cases considered.
Emerging Trends in Logistics and Their Impact on Freight Transportation Systems: A European Perspective
Authors: Zografos Konstantinos G. , Giannouli Ioanna M.
Published: April 2007

The demand for freight transportation services is a derived demand and is strongly influenced by the spatial organization and management of supply chains. In recent years, numerous trends affecting the spatial organization and structure of supply chain–logistical systems have emerged. These trends have developed as a consequence of the rapidly changing political, economic, social, and technological environments. The rational planning and design of the freight transportation system should consider these emerging trends in order to respond efficiently to the requirements imposed by the new organization of logistical systems. The objective here is twofold: first, to propose a methodological framework for developing and assessing scenarios describing the evolution of the freight transportation system characteristics due to the emerging logistical trends and, second, to apply the proposed framework to assess the future development patterns of the freight transportation system for a number of industrial sectors in Europe. The results of the proposed methodology led to identifying the relevant importance of the various logistical trends influencing the organization, utilization, and performance of the freight transportation system. The research results provide an insight into the development of the freight transportation system for different types of movement (i.e., primary, secondary, and so forth) and transportation modes. The proposed methodology provides decision makers with a tool for developing and simulating alternative policies regarding the future development of the freight transportation system.