bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Some Characteristics of Congested Flow
Authors: Banks James H.
Published: April 2007

Recent German research has suggested that there may be two qualitatively different types of congested flow, referred to as “traffic jams” and “synchronized flow.” The possible existence of synchronized flow raises a theoretical issue, since it is reported to be characterized by randomly sloped flow-density “transferences” (lines connecting adjacent points in the time series), and this may imply that there is no consistent wave direction in such flow. An analysis of flow-occupancy data from San Diego suggests that on the basis of the appearance of the data alone, two types of congested flow may be identified. These appear to be similar to, but not identical with, the two types reported in the German work; in particular, a region with positively sloped flow transferences was found. Further consideration of the data and the mechanics of congested flow suggests, however, that these two types of flow do not represent qualitatively different types of traffic behavior but rather are the result of random variations in average time gaps in the traffic stream and the relationship among speed, flow, density, and average time gap. In particular, predominantly positively sloped flow-concentration transferences do not necessarily imply that waves move downstream; rather they imply that, for data taken over short time intervals (30 s or 1 min), transferences are not a good indicator of kinematic wave speed.
Cellular Automata Microsimulation of Bidirectional Pedestrian Flows
Authors: Blue Victor J. , Adler Jeffrey L.
Published: April 2007

The cellular automata (CA) microsimulation of pedestrians is a particlehopping model in which a set of local rules prescribe the behavior of entities within local neighborhoods of cells. CA microsimulation has emerged as a tool for simulating traffic flow and modeling transportation networks. Pedestrian flow is inherently more complex than vehicular flow, and simulation models that are used for emulating vehicular traffic are not directly applicable to modeling pedestrian movements. In previous work the authors demonstrated that unidirectional pedestrian flow patterns consistent with well-established fundamental properties could be generated with CA microsimulation. This paper expands upon the previous effort and presents a CA microsimulation model and emergent fundamental flows for a bidirectional pedestrian walkway. Simulation experiments indicate that the basic model is applicable to walkways of various lengths and widths and across different directional shares of pedestrian movements.
Gas–Kinetic Model for Multilane Heterogeneous Traffic Flow
Authors: Hoogendoorn Serge P. , Bovy Piet H. L.
Published: April 2007

A gas–kinetic traffic flow model is presented that describes the traffic flow operations of heterogeneous traffic on specific lanes of a motorway. To realistically portray the multilane dynamics of traffic flow, traffic is described as a collection of vehicle platoons that consist of an unconstrained vehicle followed by a nonnegative number of constrained followers. It is shown that the gas–kinetic dynamics of this unconstrained and constrained traffic are governed by continuum and noncontinuum processes. The continuum processes describe smooth changes in the mesoscopic traffic flow variables caused by motions in the phase space. The noncontinuum processes reflect, among other things, deceleration of vehicles due to interactions between vehicles from the same and from different user classes, immediate lane changing, postponed lane changing by constrained drivers, and spontaneous lane changing by free-flowing drivers. Finally, it is shown how the multilane-multiclass model relates to traditional aggregate-lane and mixed-class gas–kinetic equations. This is accomplished by aggregation across the motorway lanes and the user classes. It is shown that the expression reflecting vehicle interactions in traditional models is only valid for dilute traffic. A remedial expression is proposed.
Congested Traffic Flow: Observations and Theory
Authors: Kerner Boris S.
Published: April 2007

Recent and some new results of observations of traffic flow dynamics in congested conditions are considered. On the basis of these results, hypotheses about properties of congested flow are proposed and discussed. In particular, it is proposed that the complexity of congested flow is linked to ( a) the existence of three qualitatively different phases in traffic flow: free flow, synchronized flow, and wide traffic jams; ( b) an occurrence of three qualitatively different types of phase transitions between these three phases of traffic flow; ( c) the result that all these qualitatively different phase transitions are related to the same class of “first-order local phase transitions;” ( d) complex dynamical behavior of synchronized flow; and ( e) the existence of two qualitatively different kinds of “nucleation effects” in traffic flow: the nucleation effect responsible for the jam’s formation, which is linked to an avalanche increase in the amplitude of an initial local perturbation of traffic variables (vehicle speed, density, or both), and the one responsible for the phase transition from free flow to synchronized flow, which is linked to an avalanche decrease in the probability of passing in free traffic flow.
Real-Time Prediction of Traffic Flows Using Dynamic Generalized Linear Models
Authors: Lan Chang-Jen , Miaou Shaw-Pin
Published: April 2007

In previous real-time flow prediction studies, the emphasis was placed on the prediction accuracy of the model. The accuracy of the prediction bounds (or limits), on the other hand, was largely ignored. Prediction bounds are, however, important input parameters in such applications as real-time stochastic traffic control, incident detection, and route guidance in the context of dynamic traffic assignment. The objectives of this study are to explore the statistical nature of traffic flows when aggregated at short time intervals and to examine the potential of using the generalized linear model in the dynamic setting to predict traffic flows and provide prediction bounds. Specifically, this study derives recursive algorithms based on the quasi-likelihood principle and performs on-line, multiple-step-ahead predictions of short-term arrival flows for signalized intersections. Preliminary results are presented using a simulated data set from CORSIM and a real data set collected from signalized intersections.
Properties of Cowan’s M3 Headway Distribution
Authors: Luttinen R. Tapio
Published: April 2007

Cowan’s M3 distribution has been used in several studies on unsignalized intersections, especially roundabouts. It allows separate analysis of follower and nonfollower headways, and it is simple enough for models of considerable complexity. Although M3 gives a simplistic model for short headways, it has many desirable properties as a headway distribution. It is possible to estimate its parameters with simple methods and with reasonable accuracy, and the estimated models give good results in the capacity analysis of unsignalized intersections. Described in this paper are the basic statistical properties of M3, and the accuracy of the method of moments and least-squares parameter estimators is evaluated. The validity of M3 in unsignalized intersection capacity analysis is evaluated by a Monte Carlo simulation with samples from M3 and semi-Poisson distributions.
Some Observations of Highway Traffic in Long Queues
Authors: Smilowitz Karen R. , Daganzo Carlos F. , Cassidy Michael J. , Bertini Robert L.
Published: April 2007

The arrival times of vehicles traveling southbound along a two-lane, bidirectional highway were recorded at eight neighboring locations upstream of a bottleneck caused by an oversaturated traffic signal. Cumulative curves constructed from these observations describe completely and in great detail the evolution of the resulting long queues. These queues formed directly upstream of the signal when the signal’s service rate fell below the southbound arrival rates, and never formed away from the bottleneck. The predictability of bottlenecks like the one studied here can be exploited to manage traffic more effectively. The behavior of vehicles within the queue, however, was rather interesting. Although the flow oscillations generated by the traffic signal were damped out within 0.8 km (0.5 mi) of the bottleneck, it was found that other oscillations arose within the queue farther upstream, at varied locations, and then grew in amplitude as they propagated in the upstream direction. Thus, the queue appeared to be stable close to the bottleneck and unstable far away. Oscillations never propagated beyond the upstream end of the queue, however; that is, the unusual phenomena always arose after the onset of queueing and remained confined within the queue. Some of these findings run contrary to current theories of traffic flow. Because the data set collected in this study is unprecedented in scope and detail and so that it may be of use to other researchers, it has been posted on the Internet and is fully described here.
Capacity Study for Protected-Permitted Phasing from Shared Lanes
Authors: Prassas Elena Shenk , Chang Jin-Il
Published: April 2007

Protected-permitted phasing from shared-use lanes (i.e., no left-turn bays) exists in certain situations where space and other constraints make this measure expedient in the face of growing traffic demand. An alternative method for handling this special case is proposed as an enhancement to the existing treatment in the 1997 update to the Highway Capacity Manual. The method proposed is logical and consistent. The more practical issue of whether it is also more accurate is addressed in a series of simulation cases. Simulation was used to provide the reference conditions because of field costs, number of variables to be controlled, and the fact that a well-established model exists. The results show that the existing method systematically overestimates lane group capacity by 10 to 25 percent for this special case, whereas the proposed alternative estimates the lane group capacity by ±10 percent or less.
Capacity of Limited-Priority Merge
Authors: Troutbeck Rod
Published: April 2007

Unsignalized intersections are the most common intersection type. They can have high cost implications for the community. A new development often has an unsignalized intersection for ingress and egress, and the basis for deciding whether an upgraded intersection is needed is based on the performance of that intersection. The concept of limited priority, in which the major-stream drivers slow and allow minor-stream drivers to enter in front of them if the average delay to the major-stream vehicles is likely to be short, is addressed. Similar behavior could also be caused by minor-stream drivers forcing their way into a priority stream. This behavior leads to a more efficient performance of the merge. Relationships to predict the capacity and the maximum delay to major-stream vehicles when drivers exhibit this limited-priority behavior are developed. The implications of the capacity of this merge type are evaluated.
Regional Architectures: Strengthening the Transportation Planning Process
Authors: Pendleton Todd A. , Sussman Joseph M.
Published: April 2007

The advent of intelligent transportation systems (ITSs) has changed the transportation planning world in three ways. First, it has created an information-rich environment, providing transportation managers with a more informed view of the “state of the network.” Second, it has high-lighted the importance of operating and managing transportation systems through the introduction of transportation services. Third, it has enabled the management of transportation systems on a regional scale. These three factors reveal the need for a framework that can ( a) guide the distribution of information and ( b) govern the deployment of services on a regional scale. A proposed framework for achieving these tasks is a regional architecture, which is conceived as a new output of the transportation planning process. Inspired by the regional architectures in the ITS context, the definition goes beyond ITS, using this concept in planning for the entire regional intermodal transportation system. Five objectives are pursued. First, “regional architecture” is defined. Second, what a regional architecture might look like is illustrated. Third, a frame-work for integrating regional architectures into the transportation planning process is proposed. Fourth, how regional architectures can address shortcomings in existing transportation planning processes is discussed. Fifth, some basic steps that transportation planners can take toward the development of a regional architecture are outlined. In pursuing these objectives, an endeavor is made to advance the state of the art in regional strategic transportation planning.
Intelligent Transportation Systems: A Two-Edged Sword for Older Drivers?
Authors: Henderson Steven , Suen S. Ling
Published: April 2007

Intelligent transportation systems (ITSs), in particular advanced transportation information systems (ATISs) and advanced vehicle control and safety systems (AVCSSs), are said to offer the opportunity to compensate for age-related reductions in sensory, perceptual, cognitive, and physical functions, making roadways safer and more accessible for all users. Closer examination reveals that these systems can be a two-edged sword. To enhance the safety of older drivers, ITSs must compensate not only for the measurable decreases in sensory and physical functions but also for the qualitative changes to cognitive processing that accompany aging. Age-related cognitive performance decrements on complex tasks, divided attention, and multiple tasks reduce the ability of older drivers to smoothly integrate concurrent driving subtasks. Several models of age effects on cognitive function are discussed. A variable-priority multipletask training strategy is suggested as the most appropriate technique for training older drivers to use new ITS technologies and to develop compensatory cognitive skills. It is concluded that careful research and design, as well as comprehensive training programs, are needed for ITSs to usefully augment the diminished capabilities of some older drivers and enhance their safety. Typical ATISs and AVCSSs are evaluated in the context of the age-related cognitive shift, implementation issues are discussed, and recommendations are made to include older drivers in the development of an extensive training program and in an ergonomic assessment of the cognitive aspects of ITS implementation.
Traffic Estimation for Proactive Freeway Traffic Control
Authors: Chin-Ping Chang Edmond
Published: April 2007

Many operating agencies are developing computerized traffic management systems that support traffic operations as part of intelligent transportation system (ITS) user service improvements. To facilitate the prediction, diagnosis, and control decisions made with uncertain information, several numerical analysis methods are available for predictive traffic control. However, these methods cannot predict short-term traffic demand accurately. A neural network approach was proposed to improve short-term traffic demand prediction for the development of advanced traffic control strategies. A promising neural network approach to improving demand prediction and traffic data modeling to support proactive traffic control was examined. Specifically, the use of time-series detector data from a real-world freeway management system that were processed through neural network models was analyzed and the results were compared with real-world observations. In all cases, the proposed neural network approach can successfully predict traffic demand patterns. The proposed study approach of combining both neural networks and error correction was found to be promising for traffic prediction. Once the neural nets are successfully trained, the system can quickly pick up traffic demand trends for proactive traffic demand management. The error correction algorithm can further smooth out errors that may be caused by sharp neural net prediction.
Learning To Associate Observed Driver Behavior with Traffic Controls
Authors: Pribe Christopher A. , Rogers Seth O.
Published: April 2007

Adaptive techniques support the development of new tools to help traffic engineers classify and evaluate traffic flow at intersections. A tool that learns to associate driver behavior with a subset of traffic controls (e.g., stoplights and stop signs) is described. In the case in which the traffic controls for an intersection are not readily available or are unknown, the tool automatically identifies the traffic controls present at an intersection from observed driver behavior. This capability may be used to augment digital maps with traffic control locations. In the case in which traffic controls are known or have previously been classified, the tool flags instances in which driver behavior is inconsistent with the traffic controls actually present. This capability might be used by various services for drivers such as dynamic routing and new safety systems. It might also be used by traffic engineers to evaluate control placement in real or simulated road networks by finding situations that elicit unusual driver behavior. The tool is calibrated with driving data for a set of segments with known controls. The tool first learns to identify the controls present on individual road segments and then uses handcrafted rules to verify control consistency across segments at intersections. The data set comprised real-world position data collected during normal daily driving. The tool accurately identified 100 percent of the data that passed verification. These results encourage belief that the system can provide traffic engineers with a reliable mapping between driver behavior and traffic controls.
Computational Issues in Micro-Genetic Algorithms for Traffic Management
Authors: Abu-Lebdeh Ghassan , Benekohal Rahim F.
Published: April 2007

Emerging artificial intelligence techniques such as genetic algorithms (GAs) allow a more realistic representation and solution of difficult and combinatorial problems such as the dynamic traffic queue management problem. Computational experience in solving such complex large-scale problems by use of micro-GAs is described. In addition to providing evidence of the ability of micro-GAs to successfully identify optimal traffic management schemes, some micro-GA-associated computational issues that warrant attention are highlighted. Choosing a proper population size is a critical decision, and internal variability must be accounted for to assess the goodness of the optimization results properly. A simple rule for deciding the best population size for micro-GAs is proposed. Micro-GAs may converge to low-quality solutions, particularly with very small population sizes; convergence of micro-GAs by itself is not a sufficient indication of good performance. The size of the search space for some real-world systems can pose some difficulties to micro-GAs. Choosing between micro-GAs and regular GAs is a problem-dependent decision.
Lessons Learned from a Review of Evaluations of Automated Highway Systems
Authors: Bret Michael James , Miller Mark A.
Published: April 2007

A review of the literature pertaining to automated highway systems (AHSs) has resulted in the documentation of lessons learned from major European and U.S. evaluations of AHSs that cover the AHS benefit assessment process. The lessons learned will be assimilated into an evaluation framework and plan, with the aim of adopting those aspects of past and present evaluations and avoiding known pitfalls. At the same time, key findings of previous AHS studies have been documented. The three products of the literature survey are as follows: a characterization of the coverage of nine categories of AHS evaluations; the identification of a sequence of evaluation phases, as planned for in nine major AHS studies; and the documentation of critical inputs to a plan for evaluating AHS concepts.
Effectiveness of Maintenance Treatments of Flexible Pavements
Authors: Eltahan Ahmed A. , Daleiden Jerome F. , Simpson Amy L.
Published: April 2007

To achieve effective pavement maintenance, the life expectancy and timing of treatment applications need to be determined. The Long Term Pavement Performance (LTPP) program includes the Specific Pavement Study-3 (SPS-3), which focuses on this subject. The treatments applied are chip seals, crack seals, slurry seals, and thin overlays. In studying the life expectancy it is not feasible to wait for all the sections in the experiment to fail. Thus, there is a need to determine the life expectancy while making efficient use of the available data collection funds. Survival data analysis is a statistical technique that meets this need by accounting for the portion of the sections in which the exact time the treatment lasted is not known. The application of this technique to flexible-pavement maintenance is presented. In addition, some results of the LTPP SPS-3 experiment are presented to the highway community. The focus is on the LTPP Southern Region. The results showed that the probability of failure was two to four times higher for the sections that were in poor condition at the time the treatment was applied than those sections that were in better condition. The median survival times for thin overlays, slurry seals, and crack seals were 7, 5.5, and 5 years, respectively. The chip-seal sections had not yet reached the 50 percent failure probability after 8 years of the SPS-3 experiment. Accordingly, chip seals appear to have outperformed the other treatments investigated in this study in delaying the reappearance of distress.
Pavement Preventive Maintenance: Key to Quality Highways
Authors: Zaniewski John , Mamlouk Michael
Published: April 2007

Highway funding is inadequate to maintain current road conditions under traditional maintenance and rehabilitation policies. Through a preventive maintenance program, pavements can be maintained in a cost-effective manner leading to a better pavement quality at lower total costs. Preventive maintenance is a program strategy that arrests light deterioration, retards progressive failures, and reduces the need for routine maintenance activities. The objective of this strategy is to extend the pavement’s functional life by applying treatments before the pavement deteriorates to a condition requiring a corrective treatment, such as a structural overlay. An effective strategy would feature a combination of treatments, such as periodic crack treatment followed by chip sealing. Several highway agencies have used preventive maintenance strategies successfully for both low-volume and high-volume roads. Flexible-pavement preventive maintenance treatments include fog seal, chip seal, slurry seal, microsurfacing, crack treatment, and thin hotmix overlays. The selection of a preventive maintenance treatment should be based on the condition of the existing pavement, traffic volume, and environmental conditions. Other factors include experience, budget constraints, and political reality. The Strategic Highway Research Program demonstrated that preventive maintenance is cost-effective for roads in the National Highway System. FHWA sponsored an implementation project to develop a preventive maintenace workshop and assist states with evaluation of preventive maintenance treatments. The workshop was presented in more than 20 states.
Development of a Laboratory Screening Test for Asphalt Pavement Crack Sealants
Authors: Van Dam Thomas J. , Reay Scott , Appleyard Marcy , Eacker Michael J.
Published: April 2007

Premature failure of crack sealants and fillers in the field calls into question the effectiveness of these materials as a treatment for cracked asphalt concrete (AC) pavements. Although standard sealant test methods ensure the consistency of the product, they fail to account for the ability of the sealant material to bond to AC, especially at cold temperatures after the material has aged. In an attempt to evaluate this behavior, a study was undertaken at Michigan Technological University, through sponsorship by the Michigan Department of Transportation. This study’s objective was to develop a laboratory testing protocol to evaluate crack sealants and fillers in an attempt to obtain better predictions of field performance. The developed protocol tests sealed AC blocks at a low temperature before and after accelerated laboratory aging to assess stiffening and failure characteristics in tension of the sealant and filler materials. To date, four laboratory phases have been completed to verify the repeatability of the testing, and preliminary correlation has been made with limited field data. The results indicate that the developed protocol is able to measure relative sealant performance in various configurations, but it is not possible to establish definitive relationships between laboratory testing and field performance at this time. Additional testing of materials, with an emphasis on field correlation, will be necessary to calibrate the test procedure.
Planning, Designing, and Implementing Heat-Straightening Repair of Bridges
Authors: Avent R. Richard , Mukai David
Published: April 2007

The use of heat straightening to repair damaged steel bridges requires careful planning and design of the repair. This planning begins with the engineer, who provides guidelines for both supervision and implementation of the repair through the supervisor and contractor. The process begins with damage assessment and includes checking for fractures, measuring the degree of damage, evaluating the degree of material degradation, and checking geometric distortion. The second step is to plan the repair by analyzing the degree of damage, determining maximum strains, selecting heating patterns, and developing a constraint plan. A methodology is provided for this planning and design. In addition, the responsibilities of the supervisor and the contractor are given. Practitioners are primarily targeted and guidelines are provided for implementing heat-straightening repairs.
FHWA’s Nondestructive Evaluation Validation Center: A National Resource
Authors: Phares B.M. , Washer G.A. , Moore M.E.
Published: April 2007

Since the inception of the National Bridge Inspection Program, much time and money have been invested in the development of nondestructive evaluation (NDE) techniques. These techniques provide bridge inspectors with tools to more accurately assess the condition of highway structures. These nondestructive evaluation methods, however, are sometimes used without a clear understanding of the factors that affect their reliability, performance, and implementation. Before NDE systems can be used with confidence, the technology and methods must be validated and all factors affecting their reliability identified. In response to this need, FHWA established the NDE Validation Center to identify and evaluate the factors affecting NDE reliability and performance. The NDE Validation Center uses a series of unique resources to evaluate and assess the factors affecting the reliability and performance of NDE systems. The Validation Center is based out of a combination of specialized laboratory and office space located at the Turner Fairbank Highway Research Center in McLean, Virginia. To supplement the capabilities of the laboratory facilities, a series of bridges located in northern Virginia and eastern Pennsylvania is used to conduct field investigations. Additionally, a collection of component test specimens is used in various test programs. The NDE Validation Center is a national resource for the evaluation of existing and emerging NDE techniques. The resources of the NDE Validation Center are available to federal and state agencies, the academic community, and industry. The Validation Center was developed to perform critical evaluations of NDE technologies and to provide a source of information and guidance to users and developers of NDE systems.
Use of Reclaimed Asphalt Pavement in Superpave Hot-Mix Asphalt Applications
Authors: Stroup-Gardiner M. , Wagner Chris
Published: April 2007

Implementation of the Superpave mix design method has encouraged the use of coarser hot-mix asphalt (HMA) mixtures, which require tight control of both the overall gradation and the percent passing the 0.075-mm (No. 200) screen. There is some concern that use of reclaimed asphalt pavement (RAP) in Superpave mixtures may be seriously limited because stockpiles of RAP may have widely variable gradations as well as high percentages of minus 0.075-mm material. The possibility of splitting RAP stockpiles by using the coarser RAP fraction in a typical 12.5 mm below-the-restricted-zone Superpave gradation has been evaluated. The finer RAP fraction was used in an above-the-restricted zone 12.5-mm Superpave gradation. Two sources of RAP (Georgia and Minnesota) were used so that a wide range of asphalt and aggregate properties would be represented. Screening the RAP allowed up to 40 percent of the coarse RAP fraction to be used and still meet below-the-restricted zone Superpave gradation requirements. This was mainly due to the significant reduction in the finer aggregate fractions, especially the minus 0.075-mm material. The use of RAP in these mixtures resulted in a savings of between 18 and 25 percent in the required neat asphalt. A noticeable increase in mixture stiffness with as little as 15 percent RAP was observed. This change in mixture properties suggested that a softer grade of neat binder might be needed. A maximum of 15 percent of the fine RAP fraction was used to produce an acceptable above-the-restricted-zone Superpave gradation. The net savings in neat asphalt content was 25 percent. Little change was observed in tensile strengths because of the addition of this RAP fraction. However, there was a substantial increase in mixture stiffness at intermediate to warm temperatures. This increase was also observed as a 20 percent reduction in the asphalt pavement analyzer rut depth when RAP was used. The indirect tensile creep compliance decreased when RAP was added. Although there was little difference in compliance at -20°C, there were decreases of about 30 and 50 percent at -10°C and 0°C test temperatures, respectively.
Ten-Year Performance Evaluation of Asphalt-Rubber Surface Mixes
Authors: Choubane Bouzid , Sholar Gregory A. , Musselman James A. , Page Gale C.
Published: April 2007

In 1988, the Florida legislature passed a bill directing the Florida Department of Transportation (FDOT) to investigate the feasibility and potential use of ground tire rubber (GTR) in asphalt-concrete mixtures. To address this legislative mandate, the FDOT planned and constructed three test projects to define performance that would allow for rational decisions about the use of GTR in Florida. A major finding of a 10-year performance evaluation of these test sites is that the wet process addition of rubber improved the crack resistance of surface mixtures. State Road 16 test sections with wet process rubberized mixes showed about 1 to 6 percent cracked areas, depending on the amount of rubber, whereas those with virgin asphalt or dry-mixed asphalt rubber showed about 30 percent cracked areas. In addition, the cracking data collected during this evaluation appear to suggest that an effective optimum rubber content is within the 10 to 15 percent range. The long-term performance evaluation program of the three test projects is described here and its findings are discussed.
Evaluation of Aggregate Size Characteristics in Stone Matrix Asphalt and Superpave Mixtures
Authors: Lynn Todd A. , Brown E. Ray , Cooley L. Allen
Published: April 2007

With any hot-mix asphalt (HMA) pavement, the applied loads ultimately must be carried by the aggregate. In addition to meeting minimum aggregate quality requirements, the proper aggregate grading must be used if the HMA is to perform satisfactorily in service. The aggregate gradation is important for ensuring that the proper aggregate structure and mixture volumetric properties are achieved. The findings of an evaluation of aggregate size characteristics—namely, nominal maximum aggregate size (NMAS) and gradation—in stone matrix asphalt (SMA) and Superpave mixtures are described here. The study objectives were twofold. The first objective was to verify that the SMA mix design procedure developed for the NCHRP 9-8 project was applicable to NMASs other than 19 mm. Second, mixture properties of SMA and Superpave mixes with the same NMASs were compared. Mixture volumetric properties, wheel tracking tests, and permeability tests were used to make comparisons. The test data indicated that the NCHRP 9-8 mix design approach for SMA mixes was indeed appropriate for various NMASs. Although differences in the wheel tracking results of the SMA and Superpave mixes were observed, none of the mixes experienced excessive permanent deformation. Permeability results for the SMA mixes indicated that, for a given NMAS, mixes with a smaller breakpoint sieve were less permeable. The SMA mixes were relatively more permeable than the Superpave mixes. Overall, the Superpave mix gradations above the restricted zone exhibited the least amount of rutting and were the most impermeable.
Effect of Flat and Elongated Coarse Aggregate on Characteristics of Gyratory Compacted Samples
Authors: Vavrik William R. , Fries Randy J. , Carpenter Samuel H.
Published: April 2007

The effect of various levels of flat and elongated (F&E) particles on the gyratory compaction characteristics in a standard bituminous mixture was examined. Compaction characteristics involve the effect of F&E particles on the void development in the gyratory compactor as well as the break-down characteristics. F&E particles could also affect the performance characteristics of the compacted mixtures. F&E particles in typical Illinois surface mixtures were examined. Two coarse aggregate sources, a dolomite and crushed gravel, were used. A cubical mixture was prepared in which all particles had an F&E ratio < 3:1 and baseline compaction characteristics were established. Coarse aggregates were individually measured to produce aggregate particles with measured F&E ratios < 3:1, between 3:1 and 5:1, and > 5:1. The coarse aggregates in the cubical gradation were replaced with various percentages of the same-sized aggregate with F&E ratios in the 3:1 and 5:1 range. These mixtures were compacted and the volumetric and gyratory characteristics were compared. Solvent extractions and binder ignition samples were obtained to indicate the relative breakdown in aggregates achieved with the different percentages of the F&E particles. The testing indicates the changes produced when different percentages of F&E particles are introduced into a mixture. When combined with performance testing, these data will provide a valid base upon which to recommend levels of allowable F&E particles in an asphalt mixture.
Hot-Mix Asphalt Volumetrics Revisited: A New Paradigm
Authors: Coree Brian J.
Published: April 2007

As early as 1905, Richardson recognized the importance to performance of the relative proportions, by volume, of the material components of bituminous mixtures. In the 1940s, Marshall explicitly addressed the volumetric percentages of air voids and of the degree of void saturation by asphalt. In the late 1950s, McLeod clearly demonstrated and justified the appropriate aggregate specific gravities to be used in volumetric computations and emphasized the importance of the combined volumes of the air voids and effective asphalt binder. These various volumetric parameters have since formed a principal part of the Marshall design method and have more recently been enshrined into the Superpave system. The definitions of the various volumetric parameters and their interrelationships are revisited here. An instructive and useful chart has been developed with which mixtures of different volumetric characteristics may be compared and, through trajectory analysis, reduced to a common basis. A further simple graphical method has been developed that may be used to analyze, volumetrically, both Marshall and Superpave mix designs. The latter method can be used as a point-estimate method to identify the binder content that will yield any given air void content. Although no new technology is presented here, old information is presented in a new way—a new paradigm.
Use of Superpave Gyratory Compactor To Characterize Hot-Mix Asphalt
Authors: Mallick Rajib B.
Published: April 2007

A method was developed to identify unstable mixes with the help of Superpave gyratory data. The basis of this method is that the primary difference in behavior of a stable mix and an unstable mix is that a stable mix gains in strength with densification and retains it through further compaction and ultimately resists lowering of voids below a particular value, whereas an unstable mix initially gains in strength but loses it beyond a certain densification point and becomes susceptible to shear failure. Hence it is proposed that the strength of a mix be evaluated at two void levels: at 5 percent, where a mix is expected to have an increased shear strength compared with postconstruction voids, and at 2 percent, where a well-performing mix should have an increased or at least similar shear strength compared with shear strength at 5 percent, and where an unstable mix is expected to have a reduced shear strength compared with shear strength at 5 percent voids. U.S. Army Corps of Engineers and Superpave gyratory compaction data were obtained for five mixes from wearing courses, and the data were evaluated with the help of in-place rutting data. The gyratory ratio, a ratio of the number of gyrations required to achieve 2 percent voids and 5 percent voids, was found to be suitable for characterizing hot-mix asphalt. Theoretical calculations and in-place rutting data show that a gyratory ratio of 4 can be used to differentiate between stable and unstable mixes—mixes with a gyratory ratio less than 4 can be expected to be unstable.
Evaluation of Superpave Repeated Shear at Constant Height Test To Predict Rutting Potential of Mixes: Performance of Three Pavement Sections in North Carolina
Authors: Tayebali Akhtarhusein A. , Khosla N. Paul , Malpass Glen A. , Waller H. Fred
Published: April 2007

The repeated shear at constant height (RSCH) test to predict the rutting potential of asphalt aggregate mixes based on field performance of pavement sections in North Carolina has been evaluated. Three pavement sections in Buncombe, McDowell, and Montgomery counties were selected based on the degree of rutting severity experienced after several years in service. The pavement section in Buncombe County showed no rutting, whereas those in McDowell and Montgomery counties showed light and severe rutting distress, respectively. Results of this study indicated that the RSCH test can clearly identify the well-performing versus poorly performing mixes (i.e., Buncombe versus Montgomery counties). Although previous studies in which the French pavement rutting tester and the Georgia loaded-wheel tester were used indicated early rutting of the pavement in Buncombe County, the RSCH test indicated that the mix was not susceptible to excessive rutting—in line with field experience of no significant pavement distress observed in this pavement. For Montgomery County, the RSCH test clearly showed that the mix was susceptible to excessive rutting with the wheelpath cores distinctly showing potential for tertiary flow—in agreement with experience of significant rutting distress observed in this pavement.
Nondestructive Evaluation of Complex Moduli in Asphalt Concrete with an Energy Approach
Authors: dos Reis Henrique L. M. , Habboub Amin K. , Carpenter Samuel H.
Published: April 2007

A modified version of the impulse-echo method is presented to nondestructively estimate the average Poisson’s ratio and the average dynamic complex bulk, shear, extensional, and longitudinal moduli of asphalt concrete specimens made of different mixtures. The estimated moduli represent an average over the volume of the specimens and over the frequency band of 10 to 50 kHz. By using principles of statistical energy analyses, the proposed methodology is based on the energydensity decay function of a diffuse wave field. The methodology allows evaluation of the energy dissipation characteristics of different asphalt concrete mixtures and their dependence on material microstructure. As a consequence, energy-density decay functions may be used to search for an optimum asphalt concrete microstructure. In this study, it was observed that the typical Superpave mixture generally exhibits higher average dynamic energy storage capacity and higher energy decay rates (i.e., loss moduli).
X-Ray Tomography of Asphalt Concrete
Authors: Shashidhar N.
Published: April 2007

The applicability of X-ray tomography techniques to image an asphalt concrete core in three dimensions and study the aggregate structure was demonstrated with four examples. It was found that rutting performance of mixes in WesTrack could be qualitatively related to aggregate structure. It was found that various aspects of a 450-mm full-depth core can be analyzed, including the aggregate structure at its interface and the void distribution and structure. Imaging a core at various stages of compaction in a gyratory compactor enabled the study of the process of compaction. The uneven distribution of asphalt in the FHWA accelerated loading facility pavements was illustrated by X-ray microtomography.
High-Occupancy Vehicle Monitoring and Evaluation Framework
Authors: Bracewell Dale , Sayed Tarek , Shalaby Amer
Published: April 2007

A framework for monitoring and evaluating the effectiveness of the arterial and freeway high-occupancy vehicle (HOV) facilities in the Greater Vancouver area of British Columbia is described. The framework evaluation objectives are categorized into three groups by their relationship to the goals of an HOV network: primary, supporting, and operational. Primary objectives directly relate to the HOV goals of improving the person throughput and encouraging higher occupancy. Characteristics of an HOV facility that contribute to the attainment of the HOV goals are evaluated as supporting evaluation objectives. Attributes that protect the performance of the HOV facility are evaluated as operational objectives. Quantifiable measures of effectiveness are selected to determine if an objective is met. The framework includes procedures to calculate the statistical reliability and relative uncertainty of the data collected. A cost-effectiveness evaluation procedure and sensitivity analysis to evaluate the economic feasibility of an HOV facility is also presented. The framework was applied to evaluate the effectiveness of the HOV facility on the Barnet/Hastings corridor. Data related to the implementation of the Barnet/Hastings HOV lane were analyzed in accordance with the framework. The results of the application are presented.
MUSIC Project: Urban Traffic Control for Traffic Demand Management
Authors: Clegg R. G. , Clune A. J.
Published: April 2007

Urban traffic control (UTC) is an inexpensive, readily available tool that is underused for travel demand management. Although it has long been understood that traffic is likely to reroute in response to signal settings, the goal of a UTC system is still often perceived as to get the vehicle through the junction as quickly as possible. The main exception is vehicle-actuated signals, which attempt to speed journeys for public transport by arranging a green-wave to transponder-equipped vehicles. There is, however, considerable potential in making use of the propensity of drivers to reroute in response to UTC, especially as a subtle tool for traffic demand management (TDM). The MUSIC (Management of traffic USIng Control) project, funded by the European Union, attempts to demonstrate some of this potential by using on-site demonstrations. In three cities, network models have been used to create fixed-time signal settings, which attempt to meet the TDM goals of the city authorities. The three sites were York, where bus-actuated presignals are used both to “gate” traffic and give priority to buses; Porto, where a citywide signal-setting policy is designed to reduce car congestion, favor well-used public transport routes, and discourage cars from entering pedestrian-sensitive areas; and Thessaloniki, where a citywide signal-setting policy is designed to reduce car congestion while favoring the most-used public transport routes. The modeling techniques used to produce the signal-setting plans are discussed, as are initial encouraging results from the demonstration sites.
Evaluating Effects of Transportation Demand Management Strategies on Trip Generation by Using Poisson and Negative Binomial Regression
Authors: Wallace Brett , Mannering Fred , Rutherford G. Scott
Published: April 2007

Most trip generation models are insensitive to the effects of transportation demand management (TDM) strategies. To evaluate the potential effectiveness of TDM solutions, transportation professionals must rely largely on the results of case studies, which cannot be generalized for all urban areas. To evaluate TDM strategies in a context that is sensitive to the unique characteristics of each urban area, TDM strategies should be incorporated into regional travel demand models. Five TDM strategies affecting trip generation rates are examined: telecommunications, alternative work schedules, on-site amenities, pricing strategies, and land use strategies. To analyze these strategies, data from the Puget Sound Transportation Panel (PSTP) were used. Variables derived from the PSTP data that may help explain the impacts of these strategies were evaluated for significance in trip generation models for several home-based and non-home-based trip purposes. The trip generation models were specified using Poisson and negative binomial regression techniques. After the models were estimated, the significance of the variables representing the impacts of TDM strategies was analyzed. Many of the TDM variables were indeed significant in the trip generation models; however, in some cases, the significance of the variables can be attributed to factors such as trip chaining, which does not describe the effects of TDM strategies. Additional research is needed to fully determine the effects of trip chaining on the variables examined in this study, and additional data could enable the development of variables that more accurately describe the effects of TDM strategies.
Critical Issues Facing Deployment of National Transportation Communications for Intelligent Transportation System Protocols
Authors: Seymour Edward J. , Patel Raman K.
Published: April 2007

Critical issues facing the deployment of the National Transportation Communications for Intelligent Transportation System Protocols (NTCIP) are discussed. NTCIP has evolved into a common communications protocol platform from which various transportation devices such as traffic controllers, variable message signs, and environmental sensor stations can be deployed. However, like any new development, the emerging NTCIP standards are facing several critical issues that practitioners must discuss and understand. Today, many municipal and state transportation professionals are inquiring about specifying NTCIP in their procurement documents. They would like to ensure that the specified products are indeed NTCIP compliant. System integrators are focusing on the mechanics of the protocols. Vendors are working to implement products consistent with intelligent transportation system standards that can be integrated into systems and will meet the needs of users. Some critical issues that have been identified through limited deployment experience with NTCIP are discussed, and guidance is provided for dealing with them. The issues include understanding the limitations of NTCIP, procurement, testing, and product availability. Finally, some details on current deployments at a few project sites in the United States are given to illustrate the underlying issues and concerns faced by transportation practitioners.