bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluating Impact on Safety of Improved Signal Visibility at Urban Signalized Intersections
Authors: Sayed Tarek , Esawey Mohamed El , Pump John
Published: February 2008

A study evaluated the safety impacts associated with improved signal visibility at urban signalized intersections. The improvements included one or a combination of the following upgrades: signal lens size, new backboards, reflective tapes added to existing backboards, and additional signal heads. Intersection collision data based on insurance claim records from the Insurance Corporation of British Columbia were used in the study to evaluate the effectiveness of the signal visibility improvement. These automobile insurance claim data are current, comprehensive, and considered quite reliable for intersection locations. Traffic volume and collision data were collected for treatment and comparison groups. The treatment group included 139 intersections and the comparison group included 85 intersections. The data for the comparison group were used to account for history and maturation confounding factors. An empirical Bayes analysis was used to ensure that the evaluation results were reliable and to account for the regression-to-the-mean confounding factor. The analysis was undertaken for both severe (injury + fatal) and property-damage-only (PDO) collisions and also for daytime and nighttime collisions. The evaluation results indicate statistically significant reductions of 8.5%, 5.9%, 6.6%, and 7.3% for PDO, daytime, nighttime, and total collisions, respectively. Severe collisions showed a nonsignificant reduction of 2.6%.
Macrolevel Collision Prediction Models to Enhance Traditional Reactive Road Safety Improvement Programs
Authors: Lovegrove Gordon R. , Sayed Tarek
Published: February 2008

The reactive use is described of 35 recently developed macrolevel collision prediction models (CPMs) to conduct a black spot study with data from 577 urban and rural neighborhoods across Greater Vancouver in British Columbia, Canada. The research objective was to investigate macrolevel CPM use in a traditional reactive safety application (macroreactive use): identification, diagnosis, and remedy of hazardous locations. The results suggested that macroreactive use has the potential to complement traditional road safety improvement programs. Several collision-prone zones were identified and ranked for diagnosis. Two zones were analyzed in detail and revealed several potential enhancements to conventional methods. If adopted for normal use by practitioners, macrolevel CPMs could facilitate improved decisions by community planners and engineers and ultimately could facilitate improved neighborhood road safety for residents and other road users.
Operational Criteria of Causality for Observational Road Safety Evaluation Studies
Authors: Elvik Rune
Published: February 2008

Nine criteria are discussed: they can be used to assess whether the effects attributed to road safety treatments in studies evaluating the effects of such treatments are causal or merely reflect randomness, confounding, or noncausal statistical association. The criteria are to a major extent based on similar criteria developed in epidemiology to assess the causality of factors associated with diseases. The criteria are related to (a) the presence of a statistical association between a treatment and changes in road safety (effect), (b) the strength of the statistical association between treatment and effect, (c) the internal consistency of the statistical association between treatment and effect, (d) the clarity of the causal direction between treatment and effect, (e) the invariance of the statistical association between treatment and effect regarding confounding factors, (f) the identification and measurement of causal mechanisms generating the association between treatment and effect, (g) the possibility of giving a theoretical explanation of the association between treatment and effect, (h) the presence of a dose-response pattern in the association between treatment and effect, and (i) the specificity of the association between treatment and effect to the intended target group of the treatment. These criteria can be used to assess the quality of road safety evaluation studies. The more criteria a study satisfies, the better is its quality. Use of the criteria is illustrated by means of examples.
Multiple-Model Framework for Assessment of Real-Time Crash Risk
Authors: Pande Anurag , Abdel-Aty Mohamed
Published: February 2008

This study is based on real-time models of risk assessment for rear-end and lane-change-related crashes on freeways. These models were developed in recent studies on the basis of historical crash data and corresponding traffic data collected through underground loop detectors on Interstate-4 in Orlando, Florida. In this study the potential of these models was explored for identification of crashes that were not part of the database used to develop the models. These crashes include single-vehicle crashes that might result from evasive actions taken by drivers to avoid vehicles in front (i.e., a rear-end crash) or in a neighboring lane (i.e., a lane-change-related crash). In addition, traffic data corresponding to rear-end and lane-change-related crashes reported on the short form (because they did not involve any injuries or loss of life) also were subjected to the models. The results indicate that the models satisfactorily identify single-vehicle crashes (other than rollovers) as well as the short-form crashes. The study also demonstrates virtual real-time application of these models over complete traffic data collected for a month. A careful analysis of the models' output on these data sets is used to make critical inferences about their expected performance in a real-time application scenario. The proposed real-time application framework for these models not only is expected to improve traffic safety but also could yield significant enhancement in traffic operation by eliminating some of the incident-related congestion.
Optimization of Highway Safety and Operation by Using Crash Prediction Models with Accident Modification Factors
Authors: Banihashemi Mohamadreza
Published: February 2008

The linear programming model that is presented optimizes the crash and delay costs of highway networks by selecting safety and operational improvements with implementation costs within a constrained budget. The costs that are minimized in this study are those of crashes plus the costs of delay times. This optimization model works with crash prediction models that estimate the expected number of crashes by using base models and accident modification factors (AMFs). In these models the base model predicts the expected number of crashes for a base highway or intersection. The AMFs modify the prediction on the basis of the specific characteristics of each highway segment or intersection. Several improvement alternatives for different highways and intersections within a network would mean many improvement combinations, each with a different cost for implementation, which would cause certain crashes and delay. The proposed model uses linear optimization to find the combination of improvements with the lowest total of crash and delay costs within an acceptable range of implementation costs. The optimization model is presented in conjunction with crash prediction models borrowed from the Interactive Highway Safety Design Model software. The optimization model could be modified to work with other types of crash prediction models. A test case study containing a network of three highways and 13 intersections is presented. The corresponding optimization problem is solved with the CPLEX software. The variations of crash and delay cost savings versus improvement costs are studied, and the results are discussed.
Application of Innovative Time Series Methodology to Relationship between Retroreflectivity of Pavement Markings and Crashes
Authors: Masliah Maurice , Bahar Geni , Hauer Ezra
Published: February 2008

The innovative time series methodology that is presented was used to examine the relationship between the safety impact of longitudinal pavement markings and their retroreflectivity. The need for the methodology was determined through an examination of the pavement marking safety literature, the desire to build on previous retroreflectivity research, and an understanding of how retroreflectivity is a function of the age of pavement markings and markers. The time series methodology involves solving for multipliers that represent the change in the expected number of crashes as a function of pavement marking retroreflectivity while simultaneously solving for seasonal effect multipliers. The time series methodology is explained in detail; its usefulness has been demonstrated through the analysis of 8 years of pavement marking and marker installation data, traffic volumes, and crash data. Safety effect multipliers were solved for yellow and white pavement markings separately and in combination. The multipliers covered different road types and crash severities by using retroreflectivity models and California's data for more than 118,000 nonintersection, nondaylight (night, dawn, and dusk) recorded crashes. To apply the time series methodology, it was necessary to develop retroreflectivity models as a function of age, color, marking material type or marker type, climate region, and amount of snow removal. The results showed that retroreflectivity levels have no effect to a small effect on the safety performance of those roadways maintained to a reasonable level of pavement marking.
Prediction of Fatality Rates for Comparison between States
Authors: Kweon Young-Jun
Published: February 2008

Comparisons using raw fatality rates (per vehicle miles traveled or per population, or both) are likely to lead to biased pictures of relative traffic safety in the states. This study attempts to provide better pictures for a state-by-state comparison by using random intercept models based on the state-level panel data from 2000 through 2004. The data include demographic economic characteristics and roadway characteristics of 46 U.S. states. Predicted fatality rates were computed with the estimated models and fixed factors tuned to the values for Virginia as a reference. New rankings were generated on the basis of predicted rates and compared with raw rankings based on the raw rates. About half of the top 10 safest states in the raw rankings dropped out of the top 10 in the new rankings, which took into account control factors. However, the uncertainty of the estimated random intercepts suggests that the new rankings can be varied considerably; this implies that the rankings should not be used as stable traffic safety yardsticks for comparison between states, although they are better than the raw rankings.
Safety Index for Evaluation of Two-Lane Rural Highways
Authors: Cafiso Salvatore , La Cava Grazia , Montella Alfonso
Published: February 2008

The methodological approach to safety evaluation of two-lane rural highway segments that is presented uses both analytical procedures referring to alignment design consistency models and safety inspection processes. A safety index (SI) that quantitatively measures the relative safety performance of a road segment is calculated from the procedure. The SI is formulated by combining three components of risk: the exposure of road users to road hazards, the probability of a vehicle's being involved in an accident, and the resulting consequences should an accident occur. This systematic and replicable procedure integrates two different, complementary approaches–one based on design consistency evaluations and the other on safety inspections–and makes it possible to address a wide variety of safety issues effectively. A further advantage of the procedure is its applicability on highways where crash data are either not available or unreliable. Validation of the procedure was carried out on a sample of roads by a comparison of the risk rank obtained by using the SI and accident history. The SI was assessed in 30 segments chosen from a sample of two-lane rural highways in Italy, and the actual accident situation was obtained with the empirical Bayes (EB) procedure. Spearman's rank correlation was used to determine the level of agreement between the rankings obtained with the two techniques. The results from the Spearman's rank-correlation analysis validate the SI, indicating that the ranking from the SI scores and the EB estimates agrees at the 99.9% level of significance with a correlation coefficient of 0.87.
Impact of Active Speed Limiters on Traffic Flow and Safety
Authors: Toledo Tomer , Albert Gila , Hakkert Shalom
Published: February 2008

Speed limiters, which control the maximum speeds of vehicles so equipped, have been proposed in recent years as speed management tools. A simulation-based evaluation is described of the impact of a wide installation of speed limiters on traffic flow characteristics and on safety. Microscopic traffic simulation is used; it models the driving behavior of individual vehicles in detail and so captures not only the impact of speed limiters on equipped vehicles but also the interaction between equipped and unequipped vehicles and the resulting impact on the latter. In the experiment, the impact is evaluated of preset speed limiters for two limiter-set speeds, 100 km/h and 120 km/h, at various desired speed distributions and congestion levels. The simulation results show that speed limiters can reduce average traffic speeds up to 10% and that the variability of traffic speeds may also be lowered. Consequently, a significant reduction in accident rates might be achieved.
Crash or Carcass Data
Authors: Knapp Keith K. , Lyon Craig , Witte Adrian , Kienert Cara
Published: February 2008

Reported animal-vehicle crashes (AVCs) and deer carcass removal have been used to define the deer-vehicle collision problem, identify its locations of concern, and evaluate its countermeasures. However, it has been shown that AVC magnitudes can be dramatically different. This research quantifies and compares the magnitude and patterns of AVC and deer carcass removal data from Iowa. Differences in these characteristics can affect the results produced by these activities. The difference in the magnitude of these two databases is confirmed, and some of the factors that may affect the size of this difference are discussed. Visual and quantitative comparisons are completed by using summary measures, geographic information system plots, and generalized linear regression models with a negative binomial error structure. This modeling approach has not been applied in the past to AVC or deer carcass removal data. AVC and deer carcass removal prediction (not causal) models for rural two-lane and multilane roadways were developed. The similarities and differences in the AVC and deer carcass removal models are discussed and the implications of these differences described. The differences found make the choice of database used critical to AVC-related roadway development decisions and policies, countermeasure location identification, and interpretation of research results. The recommendations provided focus on how AVC or carcass removal databases, as they typically exist, might be used and what improvements might be made for a more well-defined collection and application of these data.
Improving Reliability of Road Safety Estimates Based on High Correlated Accident Counts
Authors: Giuffrè Orazio , Granà Anna , Giuffrè Tullio , Marino Roberta
Published: February 2008

Calibrating a safety performance function (SPF) with many years of accident data creates a temporal correlation that traditional model calibration procedures cannot deal with. It is well known that generalized estimating equations (GEE) models are able to incorporate trends into accident data and thus overcome difficulties in accounting for correlation; the usual application of GEEs to safety analysis uses robust (or sandwich) estimates of regression coefficients under the independence hypothesis for the working correlation matrix. This practice is justified by the robustness of the GEE procedure against misspecification of the response correlation structure. Nevertheless, with this method, one has to renounce the entirety of the advantages of GEE estimates, and–especially when correlation within the subject is high–significant losses in efficiency and misleading conclusions in model interpretation can occur. In such a case, losses in efficiency of the estimates will be transferred to the reliability of the final safety estimation, for example, by the empirical Bayes method. On the basis of these considerations, the main idea of this study is that, in safety modeling, additional effort to obtain the true data correlation structure will result in better precision in the estimation of SPF parameters. An example to illustrate the methodological aspects of the proposed approach is included.
Estimating Safety Benefits of Shoulder Rumble Strips on Two-Lane Rural Highways in Minnesota
Authors: Patel Rushi B. , Council Forrest M. , Griffith Michael S.
Published: February 2008

Approximately 40% of all 2004 fatal crashes were single-vehicle, run-off-the-road (SVROR) crashes. The problem was even more significant on two-lane rural roads, where shoulder rumble strips were an important treatment in the prevention of these crashes and have proved effective on freeways. However, no studies have evaluated the effectiveness of shoulder rumble strips in reducing SVROR crashes on two-lane rural highways. An empirical Bayes before-and-after study was performed to evaluate the safety-effectiveness of milled-in continuous shoulder rumble strips on two-lane rural highways in Minnesota. The treatment was installed at 23 treatment sites (183 mi). This study reports a 13% reduction in all SVROR crashes and an 18% reduction in injury-producing SVROR crashes after installation of this treatment.
Comparison of Alternative Methods for Identifying Sites with High Proportion of Specific Accident Types
Authors: Lyon Craig , Gotts Brent , Wong Wai Kei Felix , Persaud Bhagwant
Published: February 2008

Modern road safety management programs are required to meet a number of objectives within the overall goal of reducing accidents on the road network. One of these objectives is the identification of hazardous locations through network screening. Often screening is focused on specific accident types to be mitigated by specific programs, for example, red light cameras for reducing right-angle accidents at signalized intersections. Recent methods developed for network screening utilize safety performance functions and the empirical Bayes methodology to overcome limitations in existing methods such as ignoring regression to the mean in using accident counts or rates as a ranking measure. These newer methods often are referred to as screening for the potential for safety improvement (PSI). In one version of the PSI method, sites are ranked according to their expected accident frequency; in another, sites are ranked by the expected excess frequency measured as the difference between the expected accident frequency and that expected at similar sites. This study focuses on a relatively untested method that screens for high proportions of specific accident types by using estimates of the probability that a site's observed proportion of an accident type is truly above a given critical proportion. The impacts on the method of selection for the critical proportion are examined and the efficiency of this method is evaluated by comparing its application with that of the two PSI methods for a data set of stop-controlled intersections. Results indicate that screening for high proportions may be a reasonable alternative where PSI-type approaches are not possible.
Long-Term Trends in Public Opinion following Construction of Roundabouts
Authors: Retting Richard A. , Kyrychenko Sergey Y. , McCartt Anne T.
Published: February 2008

Roundabouts can provide substantial safety and traffic flow benefits compared with traffic signals and stop signs and as a result are increasingly used in place of traditional intersections. However, construction of roundabouts can be hampered by the negative perceptions held by some drivers. Prior research has found that public support increases soon after roundabouts are built and drivers become familiar with them. The purpose of the current study was to measure longer-term changes in public opinion in six communities where stop signs or traffic signals were replaced with roundabouts. Telephone surveys were conducted approximately 6 weeks before, 6 weeks after, and 1 to 5 years after construction of the roundabouts. The proportion of drivers in favor of roundabouts ranged from 22% to 44% before construction compared with 48% to 67% soon after roundabouts were built and 57% to 87% after roundabouts were in place for at least 1 year. The majority of drivers of all ages favored roundabouts after they were in place for 1 year or more, although support was higher among younger drivers (ages 18 to 34) and lower among older drivers (65 and older). There were small but nonsignificant differences between the opinions of male and female drivers. Drivers who said the roundabouts improved safety or traffic flow, or both, had more favorable opinions of roundabouts 1 to 5 years after construction. Results indicate that public support continued to increase with time, presumably because drivers became more familiar and comfortable with this form of traffic control.
Safety Prediction Models
Authors: Hadayeghi Alireza , Shalaby Amer S. , Persaud Bhagwant N.
Published: February 2008

Urban transportation planning has traditionally focused on capacity and congestion issues with some attention paid to operation and management and with the treatment of such issues typically made proactively. In contrast, road safety has received little attention in the planning process. Safety-conscious planning is a new proactive approach that incorporates safety issues into the transportation planning process. This approach requires a safety planning decision-support tool to facilitate a proactive approach to the assessment of safety implications of alternative network planning initiatives and scenarios. The objective of this research study is to develop a series of zonal-level collision prediction models that are consistent with conventional models commonly used for urban transportation planning. A generalized linear regression modeling approach with the assumption of a negative binomial error structure was employed for exploring relationships between collision frequency in a planning zone and some explanatory variables such as traffic intensity, socioeconomic and demographic factors, land use, and traffic demand measures. Planning-level safety models developed in this study with data for the city of Toronto, Canada, are presented with illustrative applications of how they can be used as decision-support tools for planners to explicitly consider safety in the transportation planning process. Macrolevel collision modification factors are presented to illustrate how the models can be used to examine the impact of each individual planning variable on the safety of an urban zone.
Estimation of Safety Effectiveness of Changes in Shoulder Width with Case Control and Cohort Methods
Authors: Gross Francis , Jovanis Paul P.
Published: February 2008

The use of observational data to estimate safety effectiveness for changes in shoulder width is explored. Common statistical models are applied to estimate safety effectiveness of shoulder width; however, two unique approaches, the case control and the cohort methods, are used in the design stage. Case control and cohort designs are common methods in epidemiological studies; they are used to develop relationships between risk factors and disease. In highway safety, case control and cohort designs show potential for relating geometric and traffic characteristics to crashes. Case control and cohort methods produce estimates of the odds ratio and relative risk, respectively, which indicate the expected percentage change in the probability of an outcome, given a unit change in the risk factor. In the highway safety application, the odds ratio and relative risk may provide a reasonable estimate of the crash modification factor (CMF) for the risk factor in question. Geometric, traffic, and crash data were obtained for two-lane, rural, undivided highway segments in Pennsylvania. Conditional logistic regression models were developed to estimate the odds ratio for shoulder width, and Cox proportional hazard models were developed to estimate relative risk. Confounding variables were identified in the preliminary analysis and adjustments were made for confounders during the design and final analysis stages. Estimates from the two methods indicate that crashes decrease as shoulder width increases. Results are compared with the CMF presented in the Highway Safety Manual, and confidence intervals are included to illustrate the certainty of the estimates.
Lengths of Turn Lanes on Intersection Approaches
Authors: Kikuchi Shinya , Kronprasert Nopadon , Kii Masanobu
Published: February 2008

This paper examines the lengths of turn lanes when a single lane approaches a signalized intersection and is divided into three lanes: left-turn, through, and right-turn. These three lanes help to increase the capacity of the intersection by allowing more vehicles to enter the intersection during the green phase. The question is, What is the appropriate length of each turn lane? The vehicle queue pattern at the entrance to the turn lanes is examined first. The following conditions prohibit an arriving vehicle from entering the desired lane: (a) lane overflow (the lane is too short to accommodate all turning movements) and (b) lane entrance blockage (the overflow of the vehicles from other lanes blocks the entrance of the lane, even though space is available in that lane). A set of formulas to compute the probabilities of these events is developed. The lengths are calculated so that the probability that a lane does not overflow and the entrance of the lane is not blocked is greater than a threshold value. Tables of the recommended lengths are prepared for different turn volumes and threshold probabilities. These lengths are found to be shorter than what is traditionally recommended. The presence of three lanes (left-turn, through, and right-turn) allows arriving vehicles to spread among different lanes, and thus the chances of lane overflow and blockage are reduced. This is noticeable when the movements among the three directions are nearly even.
Dynamic Queuing and Spillback in Analytical Multiclass Dynamic Network Loading Model
Authors: Bliemer Michiel C. J.
Published: February 2008

A new analytical multiclass dynamic network loading (DNL) model is proposed as part of a simulation-based dynamic traffic assignment (DTA) model. In contrast to many other proposed DNL models, this model explicitly deals with queuing and spillback without relying on link travel time functions as input. Different vehicle types (e.g., cars and trucks) are considered with different speeds. Use of link travel times is likely to under-or overestimate the true travel times in a dynamic model if queues are considered. The proposed DNL model consists of a link model and a node model. The link model computes queue inflows and potential outflows, whereas the node model determines the actual outflows depending on the node structure. In the end, the link travel times are computed backward in time for each vehicle type separately. The model has been implemented in the Indy DTA software, and an application shows that the approach is viable in real-life networks.
Exploring User Behavior in Online Network Equilibrium Problems
Authors: Ukkusuri Satish V. , Patil Gopal R.
Published: February 2008

The availability of advanced traveler information systems technologies has provided opportunities for travelers to obtain online travel information and thereby improve their travel experiences. The resulting change in user behavior because of such information needs to be accounted for in traffic assignment models. A methodology that accounts for user recourse in the traffic assignment problem is proposed. This methodology accounts for the heterogeneity in user information perception by using a sequential form of logit model. Hyperpaths instead of elementary paths are used in this approach. A key difficulty in modeling online recourse in network assignment problems is in obtaining efficient hyperpaths. A methodology that uses a sequential form of logit model that obviates explicit enumeration of hyperpaths is proposed. Computational results from a hypothetical transportation network are presented to demonstrate the application of the proposed assignment approach.
Doubly Dynamic Traffic Assignment
Authors: Balijepalli N. C. , Watling D. P. , Liu R.
Published: February 2008

Properties of a doubly dynamic simulation assignment model were investigated. The model involves specifying a day-to-day route choice model as a discrete time stochastic process, combining a between-day driver learning and adjusting model with a continuous-time, within-day dynamic network loading. Such a simulation model may be regarded as the realization of a stochastic process, which under certain mild conditions admits a unique stationary probability distribution (i.e., an invariant probability distribution over time of network flows and travel times). Such a stationary state of the stochastic process is of interest to transport modelers, as one can then describe the stochastic process by its moments such as the means, variances, and covariances of the flow and travel time profiles. The results of a simulation experiment are reported in which the process of individual drivers' day-to-day route choices are based on the aggregate learning of the experienced within-day route costs by all drivers departing in the same period. Experimental results of the stationarity of the stochastic process are discussed, along with an analysis of the sensitivity of autocorrelations of the route flows to the route choice model parameters. The results illustrate the consistency of the link flow model with properties such as first in-first out, and a simple network is used to illustrate the properties.
Robust Dynamic Continuous Network Design Problem
Authors: Karoonsoontawong Ampol , Waller S. Travis
Published: February 2008

A robust optimization model is presented for the dynamic traffic assignment-based continuous network design problem, which accounts for a bilevel objective and long-term origin-destination demand uncertainty. The model also embeds Daganzo's cell transmission model. The objective minimizes the trade-off between expected total system travel time (TSTT) and expected risk. As such, the robust model provides the optimal solution that is least sensitive to the variation of travel demand, given the degree of robustness by transportation planners. The new robust model is compared with the existing network design models on a simple cell transmission test network. The robust model with greater degree of robustness yields less expected risk with the sacrifice of higher expected TSTT. The robust model yields the most robust solution, and no other model provides a satisfactory solution across the budget range. In addition, how a visualized graph may be used to elicit the preference information from transportation planners on the desired degree of robustness is illustrated.
Optimal Redesign of Dutch Road Network
Authors: Snelder M. , Wagelmans A. P. M. , Schrijver J. M. , van Zuylen H. J. , Immers L. H.
Published: February 2008

The Dutch national road network has been developed over centuries. In the past, roads were constructed according to contemporary spatial and transportation planning philosophies. Because the existing road network is a result of a long process of successive developments, the question can be asked whether this network is the most appropriate currently, especially considering the socioeconomic structure of the Netherlands. To answer this question, an optimization algorithm has been developed for designing road networks for a given spatial structure of cities, villages, and industrial activities. With this algorithm, the Dutch road network is redesigned on the basis of minimization of the travel and infrastructure costs and by taking into account the socioeconomic structure of the Netherlands. A comparison between the existing network and the new design shows that the redesigned Dutch national road network has significantly lower total costs than the existing road network. It is found that the construction of roads with more lanes on somewhat different locations leads to a reduction of the total travel time and the total vehicles kilometers traveled.
Multiple Path-Finding Models Using Kalman Filtering and Space Syntax Techniques
Authors: Lee Seungjae , Ryu Seungkyu
Published: February 2008

A study was done to develop a shortest path algorithm in which the realism of way finding had been improved by incorporating the concept of road cognition. The existing shortest path algorithms consider travel time and travel distance only. However, cognition of road configurations also can be considered for providing a realistically satisfied path. Surveys have shown that people prefer a high-cognition path rather than a low-cognition path. Therefore, the study developed a shortest path algorithm to provide a realistically plausible route that is preferred by many people and that considered the travel time, travel distance, and road cognition. The profiles of travel times, which are required to estimate arrival times up to destination, are predicted by using a Kalman filtering technique to reflect time-varying travel conditions. The travel distance is calculated by using the geographic information system (GIS) attributes, and road cognition is established by applying a space syntax technique to identify road configurations. Also, space data of the space syntax model are based on GIS data. By considering both the shortest path in terms of travel time and distance and the best cognition in terms of road configurations, multiple paths are determined.
Island Models for Stochastic Problem of Transportation Project Selection and Scheduling
Authors: Tao Xianding , Schonfeld Paul
Published: February 2008

The selection and scheduling of transportation projects can be expressed as a combinatorial optimization problem of finding the project implementation sequence that minimizes the total system cost over the analysis period. However, evaluating the total system cost is a challenging task for transportation researchers. Because of the uncertainty of travel times and project construction costs, the total system cost is usually stochastic instead of deterministic. This paper develops island models, which are variations of traditional genetic algorithms (GAs), for optimizing project selection and scheduling under resource constraints and explores the capability of the island models for solving a stochastic optimization problem. The total system cost is evaluated on the basis of equilibrium traffic assignment while a random term is introduced to emulate a stochastic environment. This work tests the sensitivity of the developed approach against the level of randomness and compares the results with those from traditional GAs. Analyses of results indicate that a well-designed island model is promising for solving a stochastic optimization problem.
Integrated Traffic Simulation–Statistical Analysis Framework for Online Prediction of Freeway Travel Time
Authors: Juri Natalia Ruiz , Unnikrishnan Avinash , Waller S. Travis
Published: February 2008

This paper introduces a novel approach to the online short-term prediction of point-to-point freeway travel time, combining statistical forecasting techniques with traffic simulation. At every freeway entrance point, a time series analysis model based on traffic detector counts is used to predict traffic demands, whose flow through the freeway segment is simulated by a cell transmission model. This procedure, applied within a rolling-horizon framework, generates online travel time predictions consistent with traffic flow theory. Experimental results obtained from synthetic data strongly suggest that the estimates obtained with this methodology are robust and accurate. For a wide range of congestion conditions and freeway segment lengths, more than half of the predictions errors were found to be smaller than 15%. Moreover, 80% of these errors fell below 40 s when the actual travel times ranged between 3 and 10 min. Further analyses of the model sensitivity to traffic detector coverage revealed that detector separations of approximately 1 mi resulted in the most precise travel time estimates. In addition to its satisfactory performance, the proposed framework is flexible, and it can make use of additional online data and easily incorporate different forecasting and simulation techniques. Therefore, this work provides a powerful tool for online travel time prediction, suitable for a variety of practical implementation conditions and requirements.
Associative Memory Techniques for Quick Estimation of Network Performance Measures
Authors: Naga R. Palavadi , Fan Yue Yue
Published: February 2008

Many important decision-making processes in transportation planning and engineering involve repetitive computation of network performance measured by total network delay, throughput, network efficiency, and other measures. The computational complexity imposed by repetitive evaluation of these measures, especially under user equilibrium conditions, is a serious obstacle to timely decision making in network-related problems. This study applies associative memory techniques, which are conceptually and computationally simple, to quick estimation of these performance measures. The results of the numerical experiments are encouraging, and the relative error on average was found to be less than 2%. Furthermore, the applicability of this approximation method to bilevel network problems, a class of important but complex problems, is explored through a study of the network recovery problem, which seeks a quick and effective repair strategy for disturbed networks following natural or human-induced disasters.
Boost Gamma Knife surgery during multimodality management of adult medulloblastoma
Authors: Germanwala Anand V. , Mai Jeffrey C. , Tomycz Nestor D. , Niranjan Ajay , Flickinger John C. , Kondziolka Douglas , Lunsford L. Dade
Published: February 2008

Object

The aim of this paper was to determine prognostic factors for adult medulloblastoma treated with boost Gamma Knife surgery (GKS) following resection and craniospinal irradiation.

Methods

The authors performed a retrospective analysis of 12 adult patients with histologically proven medulloblastoma or supratentorial primitive neuroectodermal tumor who between February 1991 and December 2004 underwent ≥ 1 sessions of GKS for posttreatment residual or recurrent tumors (6 tumors in each group). Before GKS, all patients had undergone a maximal feasible resection followed by craniospinal irradiation. Nine patients also received systemic chemotherapy. Stereotactic radiosurgery was applied to residual and recurrent posterior fossa tumor as well as to foci of intracranial medulloblastoma metastases. The median time interval from initial diagnosis and resection to the first GKS treatment was 24 months (range 2–37 months). The mean GKS-treated tumor volume was 9.4 cm3 (range 0.5–39 cm3).

Results

Following adjunctive radiosurgery, 5 patients had no evidence of tumor on magnetic resonance (MR) imaging, 3 patients had stable tumor burden on MR imaging, and 4 patients had evidence of tumor progression locally with or without intracranial metastases. All patients with tumor progression died. Eight patients survive with a mean cumulative follow-up of 72.4 months (range 21– 152 months). No acute radiation toxicity or delayed radiation necrosis was observed among any of the 12 patients. The majority of patients who achieved tumor eradication (80%) and tumor stabilization (67%) after GKS had residual tumor as the reason for their referral for GKS. The best outcomes were attained in patients with residual disease who were younger, had smaller tumor volumes, had no evidence of metastatic disease, and had received higher cumulative GKS doses.

Conclusions

Single or multiple GKS sessions were a well-tolerated, feasible, and effective adjunctive treatment for posterior fossa residual or recurrent medulloblastoma as well as intracranial metastatic medulloblastoma in adult patients.
Surgical management of cerebellar hemangioblastomas in patients with von Hippel–Lindau disease
Authors: Jagannathan Jay , Lonser Russell R. , Smith Rene , DeVroom Hetty L. , Oldfield Edward H.
Published: February 2008

Object

Despite the frequency of cerebellar hemangioblastomas in von Hippel–Lindau (VHL) disease, their optimum contemporary management has not been defined, and is made complex because of the multiple, progressive, and protean nature of the tumors found in patients with this disorder. To examine modern management and outcomes of cerebellar hemangioblastomas in VHL disease, the authors reviewed findings in patients with this disease who underwent resection of cerebellar hemangioblastomas.

Methods

Consecutive patients with VHL disease who underwent surgery for cerebellar hemangioblastoma(s) at the National Institutes of Health were included. Eighty consecutive patients (44 female and 36 male patients) underwent 126 operations for removal of 164 cerebellar hemangioblastomas (age at surgery 37.8 ± 10.3 years, follow-up duration 96.0 ± 60.3 months). Serial clinical examinations, imaging studies, and operative records were analyzed.

Results

Symptoms and signs included headache (94 operations; 75%), ataxia (55%), dysmetria (29%), and hydrocephalus (28%). Although the primary objective of surgery was resection of the hemangioblastoma considered responsible for symptoms (136 of the hemangioblastomas [83%]), 28 additional hemangioblastomas (17%) were removed during the same surgeries. Tumors associated with symptoms were larger (diameter 1.8 ± 1.9 cm; volume 2.8 ± 3.4 cm3; p < 0.05) and more likely to be associated with peritumoral edema or peritumoral cysts (100% associated with edema and/or cyst; p < 0.05) than asymptomatic tumors (diameter 1.1 ± 0.9 cm; volume 0.7 ± 0.4 cm3; 18%). More tumors were located in the posterior (74%) compared with the anterior (26%) half of the cerebellum (p < 0.05). Three months after resection, symptom improvement/stabilization had occurred following 124 of the operations (98%). Preoperative hydrocephalus resolved after tumor removal in 33 cases (94%) and did not require cerebrospinal fluid diversion. Long-term imaging follow-up (61.5 ± 15.0 months) revealed no recurrences.

Conclusions

Symptoms and signs caused by cerebellar hemangioblastomas in VHL disease are associated with edema and peritumoral cyst formation/propagation and are treated safely and effectively with resection. Cerebrospinal fluid diversion is rarely necessary after complete tumor removal in patients with preoperative hydrocephalus. Cerebellar hemangioblastomas are preferentially distributed in the posterior half of the cerebellum, as they are in the brainstem and spinal cord. Tumor recurrence is avoided by meticulous extracapsular resection.
Comparative risk of leptomeningeal disease after resection or stereotactic radiosurgery for solid tumor metastasis to the posterior fossa
Authors: Suki Dima , Abouassi Hiba , Patel Akash J. , Sawaya Raymond , Weinberg Jeffrey S. , Groves Morris D.
Published: February 2008

Object

The authors tested the hypothesis that patients with metastatic posterior fossa lesions (MPFLs) treated with resection have a higher risk of leptomeningeal disease (LMD) than those with MPFLs treated with stereotactic radiosurgery (SRS).

Methods

Between 1993 and 2004, 379 patients with MPFLs were treated with resection or SRS at The University of Texas M. D. Anderson Cancer Center. The authors' primary study outcome was the incidence of LMD, as diagnosed with cerebrospinal fluid cytological analysis and/or neuroimaging.

Results

Resection was performed in 260 patients, whereas 119 patients underwent SRS. The median patient age was 56 years, 51% of patients were male, and 93% had a Karnofsky Performance Scale score $ 70. The most common primary cancers were those of the lung, breast, and kidney, as well as melanoma. Leptomeningeal dissemination of cancer occurred in 33 patients: 26 in the resection group and 7 in the SRS group (resection group: rate ratio [RR] 2.06, 95% confidence interval [CI] 0.89–4.75, p = 0.09). Piecemeal tumor resection (137 cases) was associated with a significantly higher risk of LMD than en bloc resection (123 cases; RR 3.4, 95% CI 1.43–8.12, p = 0.006) or SRS (RR 3.37, 95% CI 1.41–8.04, p = 0.006), and there was no significant difference in the risk for LMD between en bloc resection and SRS (en bloc resection: RR 0.98, 95% CI 0.34–2.81, p = 0.98). The multivariate RR and significance associated with piecemeal resection, however, were consistent, with a strong effect (RR 2.45, 95% CI 1.19–5.02, p = 0.02) and no indication of biases associated with tumor size, location, or cystic/necrotic appearance.

Conclusions

There is an increased risk of LMD after piecemeal resection of an MPFL. This increase, although clinically and statistically significant, is not as alarming as previously reported and is absent when en bloc removal is achieved. Further assessment of the role of resection in a controlled prospective setting is warranted.
Preoperative functional magnetic resonance imaging assessment of higher-order cognitive function in patients undergoing surgery for brain tumors
Authors: Amiez Céline , Kostopoulos Penelope , Champod Anne-Sophie , Collins D. Louis , Doyon Julien , Maestro Rolando Del , Petrides Michael
Published: February 2008

Object

Resection of brain tumors has been shown to increase patient survival. The extent of the possible resection, however, depends on whether the tumor has invaded brain regions important for motor, sensory, or cognitive processes and whether the brain tissue surrounding the tumor maintains its functional role. The goal of the present study was to develop new pre- and intraoperative tools to specifically assess the function of the rostral part of the dorsal premotor cortex (PMdr) in 4 patients with brain tumors close to this region.

Methods

Using functional magnetic resonance (fMR) imaging and a task developed to assess accurate selection between competing responses based on conditional rules, the authors preoperatively assessed the function of the PMdr in 4 patients with brain tumors close to this region. In 1 patient, the authors developed an intraoperative procedure to assess performance on the task during the tumor resection.

Results

Preoperative fMR imaging data showed specific activity increases in the vicinity of the tumors, that is, in the PMdr. As confirmed by postoperative structural MR imaging, the extent of the tumor resection was optimal and the functional region within the PMdr was preserved. Furthermore, patients exhibited no postoperative deficits during task performance, demonstrating that the function was preserved. Intraoperative behavioral results demonstrated that the cognitive processes underlying performance on the task remained intact throughout the tumor resection.

Conclusions

These findings suggest that preoperative fMR imaging, together with intraoperative behavioral evaluation, may be a useful paradigm to assist neurosurgeons in preserving cognitive function in patients with brain tumors.