bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic resonance imaging and marsupialization of a hemorrhagic intramedullary vascular anomaly in the cervical portion of the spinal cord of a dog
Authors: Alexander Kate , Huneault Louis , Foster Robert , d'Anjou Marc-André
Published: February 2008

Case Description—A 1-year-old female spayed Labrador Retriever was admitted for evaluation of a progressive gait disturbance characterized by tetraparesis and general proprioceptive ataxia in all limbs.

Clinical Findings—Neurologic examination suggested a dysfunction of the C6-T2 spinal cord segments, which was slightly worse on the right side. Discomfort was suspected upon lateral flexion of the neck. Two magnetic resonance imaging (MRI) examinations at a 3-week interval revealed an intramedullary fluid-filled cavitary lesion adjacent to C7, containing a blood clot.

Treatment and Outcome—Following unsuccessful initial conservative management, surgical marsupialization of the lesion was performed through a dorsal laminectomy, durotomy, and myelotomy at C6 and C7. Histologic evaluation including immunohistochemistry was diagnostic for a vascular anomaly. Initially, the dog was nonambulatory with tetraparesis and became tetraplegic after surgery; movement was regained 6 days later. Four weeks after the procedure, the dog was able to walk unassisted. One year after surgery, the dog was actively running and jumping, with mild residual ataxia in the pelvic limbs.

Clinical Relevance—The intramedullary vascular anomaly in this dog was successfully treated with a surgical marsupialization technique. The combination of MRI, histologic eval-uation, and immunohistochemistry enabled lesion localization, evaluation of cavity content, and final diagnosis.
Light propagation in atomic Mott Insulators
Authors: Bariani Francesco , Carusotto Iacopo
Published: February 2008

We study radiation-matter interaction in a system of ultracold atoms trapped in an optical lattice in a Mott insulator phase. We develop a fully general quantum model, and we perform calculations for a one-dimensional geometry at normal incidence. Both two- and three-level L atomic configurations are studied. The polariton dispersion and the reflectivity spectra are characterized in the different regimes, for both semi-infinite and finite-size geometries. We apply this model to propose a photon energy lifter experiment: a device which is able to shift the carrier frequency of a slowly travelling wavepacket without affecting the pulse shape nor its coherence.
Interference or not: analysis of the Young’s experiment for a single-cycle pulse: Erratum
Authors: Pereira S. F. , Nugrowati A. M.
Published: February 2008

In the paper published in the J. Europ. Opt. Soc. Rap. Public. 1, 06016 (2006), the model that has been used to describe the spectral distribution of the field followed by the diffraction calculations does not lead to a pulse with a “single” cycle but to a pulse of many cycles. In this paper, we present a discussion on the subject and implications in the interpretation of the results.
Problème d'accès ou déficit de stockage ? Apport du niveau de complexité de la tâche à l'étude des troubles sémantiques lors du vieillissement pathologique : le cas de la maladie d'Alzheimer
Authors: Duarte Liliana Rico , Syssau Arielle , Jiménez Manuel , Launay Michel , Terrier Patrice
Published: February 2008

This study investigates three principal aspects of semantic memory processing in Alzheimer's disease: word finding, knowledge of the specific and generic attributes of concepts. Semantic memory is assessed by a range of verbal and visual tasks differentiated according to their level of complexity. Our hypothesis is that the processing of these types of information is modulated by the degree of effortful processing required by the tasks. The AD patients show more important difficulties on the tasks of high level of complexity. Nevertheless, although their performances improve when the level of complexity decreases, they significantly remain lower than those of the normal older subjects. These results are discussed with regard to the models of semantic memory, with particular reference to the debate in terms of a deficit of access or storage of this system in Alzheimer disease.
Evaluating the Light Falling Weight Deflectometer Device for in Situ Measurement of Elastic Modulus of Pavement Layers
Authors: Nazzal Munir D. , Abu-Farsakh Murad Y. , Alshibli Khalid , Mohammad Louay
Published: February 2008

Field and laboratory testing programs were conducted to evaluate the potential use of the light falling weight deflectometer (LFWD) device for measuring the in situ elastic modulus of pavement layers and subgrades. The field tests were conducted on several highway sections selected from different projects in Louisiana. In addition, nine test sections were constructed and tested at the Pavement Research Facility site of Louisiana Transportation Research Center. All sections were tested using the Prima 100 model-LFWD in conjunction with the falling weight deflectometer (FWD), plate load test (PLT), and dynamic cone penetrometer (DCP) tests that were used as reference measurements. Linear regression analyses were carried out on the collected test data to develop models that could directly relate the LFWD stiffness modulus with moduli obtained from FWD and PLT and the DCP penetration rate. In addition, multiple nonlinear regression analyses were conducted to develop models that could predict FWD and PLT moduli on the basis of the LFWD elastic moduli and selected soil properties (moisture content and void ratio) of the tested materials. The results showed that the FWD, PLT moduli, and DCP-penetration rate could be predicted directly with LFWD at a significant confidence level. However, the prediction models were improved when the soil properties were included as variables. Laboratory tests also were conducted to determine the influence depth of the LFWD, and the results of these tests showed that the LFWD influence depth ranged from 270 to 280 mm.
Elastic Nonlinear Finite Element Analysis of a Flexible Pavement Subjected to Varying Falling Weight Deflectometer Loads
Authors: Steven Bruce , Alabaster David , de Pont John
Published: February 2008

A nonlinear finite element method (FEM) model has been developed to model thin-surfaced, unbound granular pavements. The FEM model incorporates a nonlinear anisotropic material model for the granular material and a nonlinear material model for the subgrade. The coefficients for the material models were determined from laboratory repeated load triaxial tests. A test pavement at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF) was instrumented with an inductive coil soil strain system to measure vertical compressive strains and pressure cells to measure the vertical compressive stresses. The test pavement was subjected to loading by a falling weight deflectometer (FWD) device at four different load levels. The initial FEM model configuration was undertaken at one load level using the surface deflection measurements from the FWD; however, there were significant differences between the computed and measured stress and strain values. The scalar coefficients for the granular and subgrade materials were adjusted so that the measured and computed stress and strain values matched within a reasonable tolerance (10%). After the calibration process was finished, it was found that the computed and measured surface deflections also matched. The model was rerun with the three remaining load cases; the computed and measured stress, strain, and surface deflection values were in close agreement. The range of computed stiffness values varied with both the pavement and load level. The results from this analysis showed the need to use a full nonlinear model to obtain realistic results when FWD data are modeled.
New Approach for Estimating Rock Slope Stability Using Logistic Regression Analysis
Authors: Lee Yong Hee , Kim Jong Ryeol , Kim Daehyeon , Kang Hee Bog
Published: February 2008

Several methods for evaluating the stability of rock slopes have been proposed on the basis of site investigation data. These methods, however, may lead to considerably different results (failure or stable), depending on the subjective judgments associated with the selection of evaluation items and the application of weighting factors. To ensure fair application of the weighting factors, a new approach to evaluating the stability of rock slopes using the binary logistic regression analysis is proposed. Compared with other methods, the new approach allows the analysis of slope stability to be the most precise, with approximately 92% accuracy. This finding suggests that the statistical approach using logistic regression analysis that allows fair application of weight factors is more promising than others that require evaluators’ subjective judgments. This finding also suggests that the new approach can be useful to both practitioners and researchers in assessing the rock slope stability.
Multivariate Poisson-Lognormal Models for Jointly Modeling Crash Frequency by Severity
Authors: Park Eun Sug , Lord Dominique
Published: February 2008

A new multivariate approach is introduced for jointly modeling data on crash counts by severity on the basis of multivariate Poisson-lognormal models. Although the data on crash frequency by severity are multivariate in nature, they have often been analyzed by modeling each severity level separately, without taking into account correlations that exist among different severity levels. The new multivariate Poisson-lognormal regression approach can cope with both overdispersion and a fully general correlation structure in the data, as opposed to the recently suggested multivariate Poisson regression approach, which allows for neither overdispersion nor a general correlation structure in the data. The new method is applied to the multivariate crash counts obtained from intersections in California for 10 years. The results show promise toward the goal of obtaining more accurate estimates by accounting for correlations in the multivariate crash counts and overdispersion.
Estimating Dispersion Parameter of Negative Binomial Distribution for Analysis of Crash Data
Authors: Zhang Yunlong , Ye Zhirui , Lord Dominique
Published: February 2008

The objective of this study is to improve the estimation of the dispersion parameter of the negative binomial distribution for modeling motor vehicle collisions. The negative binomial distribution is widely used to model count data such as traffic crash data, which often exhibit low sample mean values and small sample sizes. Under such situations, the most commonly used methods for estimating the dispersion parameter–the method of moment and the maximum likelihood estimate–may become inaccurate and unstable. A bootstrapped maximum likelihood method is proposed to improve the estimation of the dispersion parameter. The proposed method combines the technique of bootstrap resampling with the maximum likelihood estimation method to obtain better estimates of the dispersion parameter. The performance of the bootstrapped maximum likelihood estimate is compared with the method of moment and the maximum likelihood estimates through Monte Carlo simulations. To validate the simulation results, the methods are applied to observed data collected at four-leg unsignalized intersections in Toronto, Ontario, Canada. Overall, the results show that the proposed bootstrap maximum likelihood method produces smaller biases and more stable estimates. The improvements are more pronounced with small samples and low sample means.
Roundabout In-Service Safety Reviews
Authors: Montella Alfonso
Published: February 2008

The number of roundabout intersections is quickly increasing around the world, mainly because of their good safety performance. However, roundabout performance can be degraded if precautions are not taken during either the design or the operation phase. Safety review methodologies are well suited for roundabout analysis, but their effectiveness can be improved substantially if the review recommendations are supported by a quantitative safety assessment. A roundabout safety assessment procedure is presented. Validation of the safety assessment procedure was carried out by a comparison of the results with empirical Bayes (EB) safety estimates. From the procedure, a safety index (SI) for roundabout approaches and for the whole number of roundabouts is assessed. The SI was assessed for 55 approaches of 15 urban roundabouts in Italy. For approaches, the correlation between the SI values and the EB safety estimates is highly significant (t = 15.62, p-value < 0.001), with 83% of the variation in the estimated number of crashes explained by the SI value. For all roundabouts, the correlation between SI values and EB safety estimates remains highly significant (t = 14.27, p-value < 0.001), with 94% of the variation in the estimated number of crashes explained by the SI value. The SI procedure makes it possible to support review recommendations by a quantitative safety evaluation. The SI can be used to rank both roundabouts and roundabout approaches by priority according to potential crash reduction from the safety measures. Furthermore, the SI procedure allows detection of safety issues that contribute the most to safety problems.
Automated Analysis of Road Safety with Video Data
Authors: Saunier Nicolas , Sayed Tarek
Published: February 2008

Traffic safety analysis has often been undertaken with historical collision data. However, well-recognized availability and quality problems are associated with collision data. In addition, the use of collision records for safety analysis is reactive: a significant number of collisions has to be recorded before action is taken. Therefore, the observation of traffic conflicts has been advocated as a complementary approach in the analysis of traffic safety. However, incomplete conceptualization and the cost of training observers and collecting conflict data have been factors inhibiting extensive application of the traffic conflict technique. The goal of this research is to develop a method for automated analysis of road safety with video sensors to address the problem of dependency on the deteriorating collision data. The method automates the extraction of traffic conflicts from video sensor data. This method should address the main shortcomings of the traffic conflict technique. A comprehensive system is described for traffic conflict detection in video data. The system is composed of a feature-based vehicle tracking algorithm adapted for intersections and a traffic conflict detection method based on the clustering of vehicle trajectories. The clustering uses a K-means approach with hidden Markov models and a simple heuristic to find the number of clusters automatically. Traffic conflicts can then be detected by identifying and adapting pairs of models of conflicting trajectories. The technique is demonstrated on real-world video sequences of traffic conflicts.
Method for Assessing Safety of Routes in a Road Network
Authors: Dijkstra Atze , Drolenga Hans , van Maarseveen Martin
Published: February 2008

In the Netherlands, the concept of sustainably safe traffic is the leading vision in road safety policy and research. The main goal of a sustainably safe road transport system is to reduce the annual number of road accident casualties to a fraction of the current levels. Important requirements resulting from this vision are that trips follow safe roads as much as possible, trips be as short as possible, and the quickest and safest routes coincide. Modeling route choice will provide answers to the planning issues of sustainably safe traffic; however, the safety effects of these requirements constitute a totally different issue, which needs to be dealt with. The focus of this study is on the design of a method that enables the planner to determine the safety effects of existing route choice and the changes in route choice. A description of road safety can be made in various ways. When a microscopic model is used, conflicts between vehicles will be an integral part of the simulation. The outcome will be used to compare the types of conflicts in a given simulation with the types of conflicts that would be acceptable in a sustainably safe road environment, for example, conflicts with opposing vehicles should be minimized at high speed differentials. A so-called route diagram of each route can be checked according to a series of criteria, each representing requirements for a sustainably safe route choice. Each criterion of the route diagram contributes to the total safety level of a route by the number of demerit points scored by the criterion. The criteria are described and tested in a microsimulation of alternative routes in a synthetic road network.
Safety Planning Study of Urban Freeways
Authors: Kononov Jake , Allery Bryan , Znamenacek Zane
Published: February 2008

Safety-conscious planning is a relatively new concept. It was developed in response to safety-related provisions of the Transportation Equity Act for the 21st Century (TEA-21) of 1998, which required explicit consideration of safety in the transportation planning process. The problem of using accident rates in transportation planning is revisited, and a case history of applying safety-conscious planning methods by the Colorado Department of Transportation is reviewed. A two-phase process that has been used to evaluate the safety impacts of multiple design alternatives is introduced. The evaluation process is based on the available safety performance functions calibrated specifically for urban freeways in concert with diagnostic investigations, pattern recognition analysis, and detailed accident diagramming. The critical importance of accident diagramming is discussed in reference to examining safety history at complex interchange locations.
Right-Angle Crash Occurrence at Signalized Intersections
Authors: Wang Xuesong , Abdel-Aty Mohamed
Published: February 2008

Right-angle crashes are prone to be severe at signalized intersections. To understand right-angle crash occurrence better and eventually to develop efficient countermeasures, this study investigated the effect of intersection traffic volume, geometric design features, and traffic control and operational features on right-angle crash occurrence at four-leg signalized intersections. Data from a total of 197 such intersections were collected from the Central Florida area. Right-angle crashes were modeled at the intersection, roadway, and approach levels. For the models at roadway and approach levels, crashes were assigned to a certain level, and then the disaggregated crashes were related to the specific roadway or approach features. The generalized estimating equations, which can account for site correlation among repeated observations from the same intersections, were used for the disaggregated models. The cumulative residuals method was used to evaluate the functional forms of the traffic volume and the models' overall performance. For the significant factors identified, the logarithm of the product of the conflicting through volumes, the number of through lanes, and the late-night and early-morning flashing operations is found to affect right-angle crash occurrence consistently. Left-turn offset, angle of the intersection, speed limit on the intersecting roadways, and yellow and all-red intervals also are significant in some models. The variables' relative significance was identified.
Identification of Intersections with Promise for Red Light Camera Safety Improvement
Authors: Hadayeghi Alireza , Malone Brian , Suggett Jeff , Reid Jeffrey
Published: February 2008

Red light cameras can be used as an alternative tool to supplement police efforts in enforcement against red light running, which is a major contributing factor to vehicle collisions at signalized intersections. The decision to install red light cameras should ensure overall improvement in traffic safety at signalized intersections. The major problem is deciding where and when to install the cameras in order to achieve the safety benefit. Therefore, guidelines are necessary for identifying and priority-ranking those intersections that have promise as sites for potential safety improvement. The primary objective of this study is to develop a safety analysis tool for estimating the safety impact of the installation of red light cameras at signalized intersections. Moreover, this research study provides a tool for identifying and priority-ranking problem intersections with respect to red light running within the entire roadway network under the jurisdiction of a particular agency. The proposed approach uses the empirical Bayes method, collision prediction models, and collision modification factors to estimate the safety changes upon installation of a red light camera at a signalized intersection. The generalized estimating equations technique with the assumption of negative binomial error distribution was used for development of the collision prediction models.
System for Digitizing Information on Wisconsin's Crash Locations
Authors: Dutta Arup , Parker Steven , Qin Xiao , Qiu Zhijun , Noyce David A.
Published: February 2008

One of the key hurdles in identifying unsafe intersections and roadways in Wisconsin is the lack of a complete crash location map, especially for crashes that occurred on local streets. Crash locations are reported in terms of relative offset from an intersection on the basis of on- and at-street name information, which identifies the intersection, and direction and distance information, which identifies the offset. For intersection crashes, the offset distance is typically set to zero. As described in this paper, the Traffic Operations and Safety Laboratory at the University of Wisconsin, Madison, has developed a system to automate the mapping of Wisconsin local road crash locations. The location mapping algorithm involves the integration of two separate Wisconsin Department of Transportation databases: the Wisconsin crash database of police traffic accident reports and the Wisconsin Information System of Local Roads (WISLR). The application of WISLR, which is an inventory of local roads with details such as traffic information, pavement condition, and roadway geometry, provides invaluable access to more comprehensive safety analysis. Although the methodology introduced is specific to these two databases, the general ideas can be applied to any similar sets of crash and geographic information system databases. The final result is a pinpoint map of all the intersection and segment crashes that occurred on local roads in Wisconsin, along with the complete crash information associated with each mapped crash. The algorithm developed with this methodology is able to map approximately 79% of the intended pool of available crashes. Quality evaluations indicate that the mapping is almost 98% accurate.
Potential Changes to 2004 Green Book's Adjustment Factors for Entrance and Exit Terminals
Authors: Fitzpatrick Kay , Zimmerman Karl
Published: February 2008

AASHTO's Policy on Geometric Design of Highways and Streets (Green Book) notes that acceleration and deceleration lengths should be adjusted on graded ramps. Factors are available in the 2004 Green Book to adjust acceleration lane and deceleration lane lengths for grades of 3% to 6%. The source of the adjustment factors was provided in the 1954 Policies on Geometric Highway Design, in which they first appeared as being based on applying “principles of mechanics to rates of speed change for level grades.” Reviews of this and other documents did not reveal a procedure for determining adjustment factors. A potential source for an adjustment factor for entrance terminals is the calculation of the distance needed to accelerate from one speed to another on different grades by means of vehicle performance equations available in the literature. Potential acceleration length adjustment factors were developed and presented in this paper. The 2004 Green Book provides equations to calculate stopping sight distances for different grades. This methodology was applied to the equations used to calculate deceleration lengths so as to determine deceleration lengths for different grades. The ratio of the deceleration length on a grade to the deceleration length on a level surface formed the basis for adjustment factors for deceleration. Actual performance of vehicles on grades and on a level surface should be measured and compared with the suggested adjustment factors to determine the accuracy of those factors.
Development of Accident Modification Factors for Rural Frontage Road Segments in Texas
Authors: Lord Dominique , Bonneson James A.
Published: February 2008

In some states, frontage roads are frequently used along freeway and fully controlled principal arterial corridors. Their primary function is to provide access between the arterial, or freeway, and adjacent developed property. Little information about the safety performance of rural frontage roads exists. This paper describes the development of a safety performance function (SPF) and accident modification factors (AMFs) for rural frontage road segments. Both one-way and two-way frontage road operations are addressed. The AMFs quantify the relationship between specific changes in geometric design and road safety. The findings from this research show that wider lanes and shoulders are associated with a reduction in segment-related collisions. In addition, the data suggest that the presence of edge marking has an impact on rural two-way frontage road safety. The SPF developed for this research indicates that, for the same traffic volume, rural frontage road segments experience about the same number of severe crashes as typical rural two-lane highways.
Decision Support System for Predicting Benefits of Left-Turn Lanes at Unsignalized Intersections
Authors: Ranade Sarang , Sadek Adel W. , Ivan John N.
Published: February 2008

Accommodating left turns at unsignalized intersections is one of the most challenging problems in traffic engineering. Over the past 40 years, a few studies developed guidelines to help traffic engineers in deciding when a left-turn lane was warranted for a given situation. Building on these previous attempts, the current study develops a refined decision support system (DSS) for assessing the likely benefits of left-turn lane installations as an aid in deciding whether a left-turn lane is warranted. The developed DSS is designed to predict these likely benefits on the basis of several measures, including delay savings, reductions in percentage of stops, increases in fuel efficiency, and reductions in emissions. The first step in development of the DSS was the use of microscopic simulation to model several real-world unsignalized intersections with different geometric configurations located in different area types. After careful calibration of these models, several scenarios covering a wide range of operational conditions were simulated. The output from these simulation runs was used to train a set of multilayer perceptron neural networks (NNs) and to generalize the results from the models' runs. The NNs were then incorporated into a DSS that can help an analyst quantify the impacts of a proposed new development as well as estimate the benefits of installations of left-turn lanes. The paper concludes by summarizing some conclusions derived from the study.
Operational and Safety Effects of Right-Turn Deceleration Lanes on Urban and Suburban Arterials
Authors: Potts Ingrid B. , Ringert John F. , Harwood Douglas W. , Bauer Karin M.
Published: February 2008

Right-turn deceleration lanes reduce the potential for rear-end collisions from vehicles slowing to make right-turn maneuvers. Right-turn lanes also improve arterial capacity by removing slower-moving vehicles from the main traffic stream. Transportation agencies must have an understanding of the traffic operational and safety effects of right-turn lanes to determine effectively where right-turn lanes are needed. Therefore, in this research, a computer simulation study of motor vehicles and pedestrians at right-turn lanes was conducted to determine their operational effects. A benefit-cost analysis of right-turn lanes that considered both their operational and safety effects was performed. The research indicates that right-turn maneuvers from a two-lane arterial at an unsignalized intersection or driveway can delay through traffic by 0 to 6 s per through vehicle where no right-turn lane is present. Delays to through traffic due to right turns in the same situation on a four-lane arterial are substantially lower, in the range from 0 to 1 s per through vehicle. Pedestrians at unsignalized intersections or driveways can have a substantial impact on delay to through vehicles due to slowing of right-turning vehicles yielding to pedestrians. Provision of a right-turn lane can reduce pedestrian-related delays to through traffic by as much as 6 s per through vehicle, depending on pedestrian volume. Also presented is an economic-analysis procedure that can identify unsignalized intersections and major driveways at which provision of right-turn lanes is cost-effective.
Placement Design of Ramp Control Signals
Authors: Wang Zhongren
Published: February 2008

Some current design guidelines specify that standard-mounted ramp control signals be placed almost aligned with the limit line. As a result, signal indications are typically placed outside of a driver's comfortable cone of vision, as required by the Manual on Uniform Traffic Control Devices (MUTCD). In this paper, the placement design of ramp control signals was analytically examined in relation to the satisfaction of a driver's comfortable cone of vision for stopped vehicles at the limit line and the satisfaction of stopping sight distance for approaching vehicles in accordance with MUTCD. Relationships between location of limit line, location of signal standard, ramp geometry, and approaching speeds were derived. Sample lookup design charts were also developed to facilitate the development and evaluation of signal placement design. A brief analysis using these relationships concluded that signal standards placed in alignment with the limit line would violate not only the comfortable cone of vision of stopped drivers but also the stopping sight distance of approaching vehicles. For a loop on-ramp with a 300-ft radius, standard-mounted signals on the left side of an on-ramp should be placed at least 22 ft downstream of the limit line to satisfy the requirements of both the stopped and approaching vehicles. In contrast, signals on the right side could satisfy only the stopped vehicles but not the approaching vehicles if placed at least 44 ft downstream of the limit line. (Left and right here are relative to the direction of travel.) Therefore, signals placed on the left side of the on-ramp curve (even with a radius of 500 ft) are more critical than those on the right side, especially when the approaching stopping sight distance is important.
Urban Freeway On-Ramps
Authors: Yi Hanwen , Mulinazzi Thomas E.
Published: February 2008

In this paper the influences of the ramp flow on the freeway flow are deemed invasive influences because the freeway vehicles' priority is violated and the freeway flow is interrupted. Understanding of the invasive influences of the freeway entry process helps to promote efficient and safe operations of the main-line facility and to identify more straightforward indicators of level of service (LOS) for freeway on-ramp segments. First, on the basis of field observations conducted at three on-ramp sites along I-35 within the greater Kansas City, Kansas and Missouri, metropolitan area, ramp merging behavior of vehicles in platoons was identified as the direct cause of invasive influences on the freeway flow. Then, the significance of the invasive influences was evaluated in accordance with the evasive events performed by freeway drivers. These evasive events, instigated by merging conflicts, include slowdown and lane change actions. Finally, more straightforward LOS indicators were recommended for improving the current (2000) Highway Capacity Manual LOS evaluation procedure for freeway on-ramp segments.
Potential Updates to 2004 Green Book's Acceleration Lengths for Entrance Terminals
Authors: Fitzpatrick Kay , Zimmerman Karl
Published: February 2008

AASHTO's Policy on Geometric Design of Highways and Streets (Green Book) notes that drivers entering a highway from a turning roadway accelerate until the desired highway speed is reached. Because the change in speed is usually substantial, provision is made for acceleration to be accomplished on an auxiliary lane, called an acceleration lane, to minimize interference with through traffic and to reduce crash potential. The 2004 Green Book contains acceleration lane lengths. The procedure identified to reproduce these values assumed running speed for the limited-access highway and the ramp along with acceleration rates from 1930s studies. Potential acceleration length values were then calculated by (a) updating the assumptions within the identified procedure and (b) using spreadsheets that can generate second-to-second acceleration. Findings from recent studies were compared with the existing Green Book values and the calculated suggested acceleration lengths. The suggested lengths determined in this paper, which are based on more realistic speed assumptions, more current acceleration lengths, and findings from recent research, are longer than the values in the Green Book. The paper recommends that additional research be done on acceleration lengths to determine whether the Green Book values should be increased.
Dynamic Traffic Equilibrium
Authors: Ramadurai Gitakrishnan , Ukkusuri Satish V.
Published: February 2008

The existence of equilibrium solutions in single-bottleneck models with homogeneous travelers having the same preferred arrival times is explored from both theoretical and experimental frameworks. First, an equal payoff solution obtained in past studies is proved not to be in dynamic user equilibrium (DUE). Necessary conditions for DUE are presented, and the nonexistence of DUE in a single-bottleneck model with homogeneous commuters is proved. Second, a multiplayer online experimental network game that emulates the single-bottleneck model is discussed. The game is played online by real players and is repeated 21 times, each under no-information and online-information settings. The experimental setup and the results are described with insights from graphical plots and analysis. Specific emphasis is placed on the system's dynamic evolution in each game and the pattern of a user's decision making. It is anticipated that these results will provide important insight into the underlying behavioral decision making of travelers and will thereby facilitate the development of better dynamic traffic assignment models.
Alpha Reliable Network Design Problem
Authors: Chen Anthony , Kim Juyoung , Zhou Zhong , Chootinan Piya
Published: February 2008

Uncertainties are unavoidable in engineering applications. A new model is proposed for designing networks under uncertainty of future demands. The objective is to minimize the total travel time budget required to satisfy the total travel time reliability constraint while considering the route choice behavior of network users. The model adopts the value-at-risk risk measure instead of the utility function to model planner risk preferences. It allows the planners to specify their risk preferences by using a confidence level of alpha on the total travel time reliability. This alpha reliable network design model is formulated as a stochastic bilevel optimization problem. The upper-level subprogram is a variant of the chance-constrained model that minimizes the total travel time budget subject to a chance constraint with a user-specified confidence level, a budget constraint, and design variable constraints; the lower-level subprogram is a user-equilibrium problem under demand uncertainty. A simulation-based genetic algorithm procedure is developed to solve this complex network design problem (NDP). Two numerical examples are presented to illustrate the features of the proposed NDP model.
Sensor Coverage and Location for Real-Time Traffic Prediction in Large-Scale Networks
Authors: Fei Xiang , Mahmassani Hani S. , Eisenman Stacy M.
Published: February 2008

The ability to observe flow patterns and performance characteristics of dynamic transportation systems remains an important challenge for transportation agencies, notwithstanding continuing advances in surveillance and communication technologies. As these technologies continue to become more reliable and cost-effective, demand for travel information is also growing, as are the potential and the ability to use sensor and probe information in sophisticated decision support systems for traffic systems management. This paper focuses on improving the efficiency of data collection in transportation networks by studying how sensor placement affects network observability. The objective of this study is to identify a set of sensor locations that optimize the coverage of origin–destination demand flows of the road network and maximize the information gains through observation data over the network, while minimizing the uncertainties of the estimated origin–destination demand matrix. The proposed sensor models consider problems where the numbers of sensors are limited and unlimited. The paper also provides several examples to illustrate the relative effectiveness of the proposed methodologies.
Approach to Time Dependence and Reliability in Dynamic Route Guidance
Authors: Kaparias Ioannis , Bell Michael G. H. , Bogenberger Klaus , Chen Yanyan
Published: February 2008

This paper presents a methodology for increasing the reliability of route suggestions in route guidance systems. The procedure, based on the A* path-finding algorithm and Chen's link penalty method, involves penalizing links with a high risk of being congested and obtaining a set of reliable route suggestions. Time dependence of travel times is considered by adapting the flow–speed model technique accordingly. The structure of the path-finding algorithms is also modified to account for real road network features. Finally, experiments using simulated travel time and reliability data are carried out on a road network, and the results are discussed.
Flexible Multipath Search Algorithm for Multipurpose Location-Based Activities
Authors: Jeong Yeon J. , Hong Young-Chae , Kim Tschangho John
Published: February 2008

An algorithm is developed that provides not only least-cost alternate routes but also ones that are close to the least-cost routes for users to select from multiple paths that route through points of interest. The algorithm utilizes a link-based search method rather than the traditional node-based search method. The link-based algorithm is able to use the existing transportation network by allowing U-turns and restricting left turns without modifications. The algorithm also uses relative prices rather than absolute prices in selecting paths. The relative price is the difference between the minimum price available in the market and the price that is available on a path. Introduction of relative prices enables the provision of flexible route guidance to meet the various needs of users. The algorithm developed has been applied to a virtual network, which successfully demonstrated the implementation of the multipath search algorithm for multipurpose activities.
Calibrating Dynamic Network Models for Traffic Operator Decision Support
Authors: Hoogendoorn Serge P. , Schreuder Marco , Hoogendoorn-Lanser Sascha
Published: February 2008

To support traffic operators in regional traffic management centers with their network control tasks, the Traffic Research Center of the Dutch Ministry of Transportation has proposed a two-step scenario-based approach. In the first step, traffic engineers prepare candidate traffic control scenarios that are likely to resolve problems that occur in real-world network traffic operations. In the second step, network operators can try out a limited number of control scenarios with an online prediction system to see which of these best resolves the problems at hand. To prepare the scenarios, a scenario assessment system is used that predicts the impacts of a specific control scenario by using a dynamic network traffic flow model (MetaNet). The development of a fully automated calibration approach for the input and parameters of this macroscopic network simulation model is described. The approach presented consisted of four steps—preparing inflows and turning proportions, establishing lane-specific traffic flow parameters, estimating the global simulation parameters, and determining unresolved model inputs—eventually leading to input data and a set of parameters that yield the best prediction of networkwide traffic conditions. Furthermore, the approach checks the available input data for inconsistencies in terms of network configuration and measurement errors. On the basis of the application examples tested, the approach is well suited for the calibration task at hand, yielding a remarkable improvement in the prediction error. Furthermore, the computation time for a realistic network is sufficient for most practical applications.
Investment in Transportation Network Capacity under Uncertainty
Authors: Sun Yao , Turnquist Mark A.
Published: February 2008

A model of investment planning for transportation networks is formulated. The model seeks to maximize expected system capacity subject to uncertainty that will occur in the future demand pattern and with a limited budget for investment. Simulated annealing is used to solve the investment planning problem. A case study of a simplified version of the western U.S. double-stack container network is included to illustrate the application of the model.
Steepest Descent Day-to-Day Dynamic Toll
Authors: Yang Fan , Yin Yafeng , Lu Jiangang
Published: February 2008

Day-to-day dynamic congestion pricing schemes have been recently proposed to force the traffic system to evolve from the status quo to a stationary state of system optimum instead of user equilibrium, considering drivers’ day-to-day behavior adjustments. From the perspective of traffic management, it may be desirable to expedite the evolution process such that the total travel cost across the process can be reduced. A novel steepest descent dynamic toll scheme is proposed that minimizes the derivative of the total system cost with regard to day t or reduces the total system cost the most for each day. The problem of finding the steepest descent scheme is first formulated as a piecewise linear nonsmooth optimization problem and then transformed into a standard linear programming problem. Its mathematical properties are discussed further and a solution procedure is proposed for specifying the steepest descent pricing scheme. A numerical study of the well-known Braess network and the Sioux Falls, South Dakota, network is conducted to compare the performance of different dynamic pricing schemes.
Rate of spontaneous hemorrhage in histologically proven cases of pilocytic astrocytoma
Authors: White J. Bradley , Piepgras David G. , Scheithauer Bernd W. , Parisi Joseph E.
Published: February 2008

Object

Spontaneous intracerebral hemorrhage is an uncommon but recognized initial presenting sign of both primary and metastatic brain tumors. The rate of tumor-related intracranial hemorrhage is variably reported from < 1 to 14.6%. Hemorrhage in primary gliomas occurs in 3.7–7.2% of gliomas, mainly in glioblastoma muliforme and oligodendroglioma with low-grade astrocytomas accounting for < 1%. Hemorrhage associated with pilocytic astrocytomas (PAs) is only sporadically reported. The authors report on a series of patients in whom PAs presenting as hemorrhages prompted them to examine the incidence of bleeding in these tumors.

Methods

Cases involving a confirmed tissue diagnosis of PA from 1994–2005 were reviewed retrospectively. The authors included only patients with evidence of hemorrhage on computed tomography and/or magnetic resonance imaging seen prior to biopsy or resection and in the absence of trauma or other vascular pathological entities.

Results

In 138 patients with histologically proven PAs, the mean age at diagnosis was 23 years. In 11 patients (8%; 5 male and 6 female) there was evidence of hemorrhage at presentation. There were no locations more susceptible to hemorrhage than any other, although no bleeding occurred within the cerebellum. All but 1 patient was treated with a gross-total resection.

Conclusions

Hemorrhage in association with PAs likely results from the frequently observed abnormal vasculature in these tumors, occurs with a greater frequency than previously thought, and should be considered in the differential diagnosis of spontaneous intracerebral hemorrhage.
Seizure characteristics and control following resection in 332 patients with low-grade gliomas
Authors: Chang Edward F. , Potts Matthew B. , Keles G. Evren , Lamborn Kathleen R. , Chang Susan M. , Barbaro Nicholas M. , Berger Mitchel S.
Published: February 2008

Object

Seizures play an important role in the clinical presentation and postoperative quality of life of patients who undergo surgical resection of low-grade gliomas (LGGs). The aim of this study was to identify factors that influenced perioperative seizure characteristics and postoperative seizure control.

Methods

The authors performed a retrospective chart review of all cases involving adult patients who underwent initial surgery for LGGs at the University of California, San Francisco between 1997 and 2003.

Results

Three hundred and thirty-two cases were included for analysis; 269 (81%) of the 332 patients presented with ≥ 1 seizures (generalized alone, 33%; complex partial alone, 16%; simple partial alone, 22%; and combination, 29%). Cortical location and oligodendroglioma and oligoastrocytoma subtypes were significantly more likely to be associated with seizures compared with deeper midline locations and astrocytoma, respectively (p = 0.017 and 0.001, respectively; multivariate analysis). Of the 269 patients with seizures, 132 (49%) had pharmacoresistant seizures before surgery. In these patients, seizures were more likely to be simple partial and to involve the temporal lobe, and the period from seizure onset to surgery was likely to have been longer (p = 0.0005, 0.0089, and 0.006, respectively; multivariate analysis). For the cohort of patients that presented with seizures, 12-month outcome after surgery (Engel class) was as follows: seizure free (I), 67%; rare seizures (II), 17%; meaningful seizure improvement (III), 8%; and no improvement or worsening (IV), 9%. Poor seizure control was more common in patients with longer seizure history (p < 0.001) and simple partial seizures (p = 0.004). With respect to treatment-related variables, seizure control was far more likely to be achieved after gross-total resection than after subtotal resection/biopsy alone (odds ratio 16, 95% confidence interval 2.2–124, p = 0.0064). Seizure recurrence after initial postoperative seizure control was associated with tumor progression (p = 0.001).

Conclusions

The majority of patients with LGG present with seizures; in approximately half of these patients, the seizures are pharmacoresistant before surgery. Postoperatively, > 90% of these patients are seizure free or have meaningful improvement. A shorter history of seizures and gross-total resection appear to be associated with a favorable prognosis for seizure control.