bluuebunny/crossref_metadata_2025 huggingface dataset:
Why Field Measurements Differ from Model Estimates: Analysis Framework for Capacity and Level-of-Service Analysis of Unsignalized Intersections
Authors: Kyte Michael , Dixon Michael , Basavaraju Purushotham Murali
Published: April 2007

Several questions are considered relating to the variability between field measurements and model forecasts, with a focus on the need to moderate user expectations about this variability. Considered first are the degree of variability observed in field measurements of delay and the stochastic effects in delay estimates produced by microscopic simulation. Examined next are the structure of the models of two-way stop-controlled (TWSC) intersection capacity and delay and how this structure might cause differences between field measurements and model estimates. How much the end user can moderate these differences using backcalculations, observation, and calibration and a “correct” perspective for the end user regarding these differences and variability are also discussed. These questions are considered using data collected as part of the NCHRP project used to develop the TWSC intersection capacity and level-of-service procedures contained in the Highway Capacity Manual models.
Estimating Values for Traffic Parameters in Turning Lanes
Authors: Coeymans A. Juan Enrique , Herrera M. Juan Carlos
Published: April 2007

Following previous research in Chile that showed the influence of physical and operational characteristics of traffic signal junctions on capacity, in-depth research was done to capture the influence of turning vehicles as opposed to other vehicles sharing a lateral lane. Currently, equivalency factors and then saturation flows are estimated as a function of lane type and width, period of the day, and the proportion of public transport vehicles in the flow. A database containing more than 400 discharges and about 4,000 headways was collected at 12 signalized junctions in Santiago, Chile, and using the synchronous regression method, new formulations were obtained to estimate equivalency factors. These formulations were defined, besides the above-mentioned factors, as a function of turning-vehicle proportion, turn radius, and pedestrian level that interfere with turning vehicles. Validation of the results was successful. The difference between observed and estimated saturation flows was about 1%, which is an excellent accuracy level. In fact, it is far better than current estimations. As a result, a better and more realistic estimation for saturation flow in turning lanes in developing countries was obtained, and therefore, in order to improve traffic signal junction performance, the new formulations can be introduced into computational programs for simulation and optimization of different urban traffic projects.
Saturation Flow Rate, Start-Up Lost Time, and Capacity for Bicycles at Signalized Intersections
Authors: Raksuntorn Winai , Khan Sarosh I.
Published: April 2007

A review of the literature shows that capacity and saturation flow rate for on-street bicycle lanes at intersections have not been measured on the basis of bicycle discharge at intersections at the start of the green phase. The Highway Capacity Manual 2000 recommends a saturation flow rate of 2,000 bicycles per hour for a bicycle lane at a signalized intersection. However, this recommendation is not based on field studies at the intersection and is not a function of the width of the bicycle lane. A revised estimate is provided of saturation flow rate, and an estimate is provided of start-up lost time for bicycles based on data collected at the stop line of signalized intersections. In addition, the lateral stopped distance of automobiles from bicycle lanes, the lateral stopped distance of bicycles from adjacent lanes, and the lateral and longitudinal stopped distance between pairs of bicycles at a signalized intersections are presented. Bicycles may form more than one queue within a bicycle lane at the stop line. Since bicycles maintain a certain distance from the adjacent lane and the curb, the number of queues formed varies based on the width of the bicycle lane. Therefore, the saturation flow rate for a bicycle lane depends on the number of queues or the width of the bicycle lane. The saturation flow rates for bicycle lanes of varying widths are proposed on the basis of the lateral stopped distance of bicycles. Empirical evidence from intersections in Colorado and California is used to propose a new method to estimate the capacity for a bicycle lane.
Toward Benchmarking of Microscopic Traffic Flow Models
Authors: Brockfeld Elmar , Kühne Reinhart D. , Skabardonis Alexander , Wagner Peter
Published: April 2007

Several microscopic traffic flow models were tested with a publicly available data set. The task was to predict the travel times between several observers along a one-lane rural road, given as boundary conditions the flow into this road and the flow out of it. By using nonlinear optimization, the best matching set of parameters for each of the models was estimated. For this particular data set, the models that performed best were the ones with the smallest number of parameters. The average error rate of the best models is about 16%; however, this value is not very reliable: the error rate fluctuates between 2.5% and 25% for different parts of the data set.
Test of Behavioral Theory of Multilane Traffic Flow: Queue and Queue Discharge Flows
Authors: Banks James H. , Amin Mohammad R.
Published: April 2007

Daganzo recently proposed a behavioral theory of multilane traffic flow. This theory is the basis for several predictions related to flow phenomena, including several about the way that the relative speeds and flows in different lanes change in transitions to and from congested flow. In particular, the theory asserts that the more aggressive drivers (referred to as “rabbits”) always behave so as to maximize their speed. In congested flow, speeds are assumed to be nearly equal for all the lanes, and rabbits distribute themselves across the lanes so as to maintain this equality of speed. In acceleration downstream from queues, the equality of speed among the lanes breaks down once the free-flow speed of the slowest lane is reached, and the rabbits segregate themselves in the fastest lane. This redistribution of flow is expected to lead to two distinct flow states in queue discharge: capacity flow and discharge flow. Because the transition from capacity flow to discharge flow may lead to different overall flows and densities in the two states, a wave marking the transition between them may move either upstream or downstream. Automatically collected flow, occupancy, and speed data from freeways in the San Diego and Toronto areas were used to test these features of the theory at merge bottlenecks and in queue discharge following the removal of incidents. It was found that there are often speed differences among the lanes even in congested flow and that sudden redistribution of flow across the lanes can occur without speed equalization. These findings imply that Daganzo’s behavioral logic is oversimplified and that something more than just maximization of speed by aggressive drivers is involved in the distribution of flow across the lanes.
Numerical Analysis of Freeway Traffic Flow Dynamics for Multiclass Drivers
Authors: Zhu Zuojin , Chang Gang-len , Wu Tongqiang
Published: April 2007

A first-order multiclass model is presented for illustrating freeway traffic dynamics, especially regarding the temporal and spatial variation of both densities and flow rate along freeway segments without the disturbance from ramp flows. The proposed macroscopic model is grounded on the assumption that freeway traffic may consist of multiple classes of drivers who, characterized by their unique speed–density relation, are likely to react differently under the same driving environment. The distribution of various classes of drivers and their differences in responding to perceived driving conditions may contribute significantly to the observed freeway traffic dynamics that remain to be better explained by existing traffic flow theories. The numerical solution and simulation results reported in this study, however, indicate that this proposed first-order multiclass model offers the potential to explore the complex interactions between freeway drivers and their collective impact on traffic flow patterns.
Macroscopic Model and Its Numerical Solution for Two-Flow Mixed Traffic with Different Speeds and Lengths
Authors: Chanut Stéphane , Buisson Christine
Published: April 2007

A new first-order traffic flow model is introduced that takes into account the fact that various types of vehicles use the roads simultaneously, particularly cars and trucks. The main improvement this model has to offer is that vehicles are differentiated not only by their lengths but also by their speeds in a free-flow regime. Indeed, trucks on European roads are characterized by a lower speed than that of cars. A system of hyperbolic conservation equations is defined. In this system the flux function giving the flow of heavy and light vehicles depends on total and partial densities. This problem is partly solved in the Riemann case in order to establish a Godunov discretization. Some model output is shown stressing that speed differences between the two types of vehicles and congestion propagation are sufficiently reproduced. The limits of the proposed model are highlighted, and potential avenues of research in this domain are suggested.
Gas-Kinetic Traffic Flow Modeling Including Continuous Driver Behavior Models
Authors: Tampère C. M. J. , van Arem B. , Hoogendoorn S. P.
Published: April 2007

A modeling technique is presented that analytically bridges the gap between microscopic behavior of individual drivers and the macroscopic dynamics of traffic flow. The basis of this approach is the (gas-) kinetic or mesoscopic modeling principle that considers the dynamics of traffic density and generalizations thereof as a probability density function of vehicles in different driving states. In contrast to traditional kinetic models, deceleration of individual vehicles due to slower traffic is treated as a continuous adaptive process rather than a discrete event. An analytic procedure is proposed to aggregate arbitrarily refined individual driver behavior to a macroscopic expected acceleration or deceleration of flow as a whole that can be used in macroscopic differential equations for traffic flow. The procedure implicitly accounts for the anisotropy of information flow in traffic, for anticipation behavior of drivers, and for the finite space requirement of vehicles, as long as these properties have been specified at the level of individual driver behavior. The procedure is illustrated for a simple car-following model with overtaking opportunity. The results show that the procedure yields micro-based aggregate traffic flow models that capture the essential properties of traffic dynamics. The techniques presented can contribute to the development of traffic flow models with driver behavior and driver psychology as important explanatory factors of congestion formation and propagation. Moreover, the approach allows building macroscopic traffic flow equations from future traffic flows for which no empirical speed–flow–density relations are available yet.
Capacity and Queue Modeling for On-Ramp–Freeway Junctions
Authors: Albanese Marina , Camus Roberto , Longo Giovanni
Published: April 2007

With reference to the procedure in the Highway Capacity Manual (HCM) 2000 for estimation of measures of effectiveness, a model is proposed to estimate merge-area capacity and to predict traffic dynamics and queue evolution for on-ramp–freeway junctions. The aims of the study are to analyze the behavior of flows within the merge area and to propose a methodology to dynamically estimate the capacity of both ramp and main line according to inflow patterns and to develop a mesoscopic model of merge facilities that allows the prediction of merge-area traffic outflow according to inflow patterns and to estimate traffic queue dynamics. The most relevant finding of the study is a methodology for estimation of the capacity of the merge area referred separately to both the main line and the ramp. The proposed approach could be considered as a link between the HCM hypotheses and those of gap-acceptance theory; the capacity of the competitive streams within the merge area depends on the opposing traffic volumes. The model gives information about traffic flows and queue dynamics (including total delay and maximum queue length). The first results of the application to a case study are briefly discussed, and some further developments are suggested.
Creating Asset Management Reports from a Local Agency Pavement Management System
Authors: Dewan Shameem A. , Smith Roger E.
Published: April 2007

Reporting assets is an essential component of an asset management system. While asset management covers management of the whole range of assets an agency owns, several types of reports need to be produced depending on the types of assets and the purpose of reporting. These reports are used to convince lawmakers and taxpayers to allocate funds needed to keep the assets in a desirable condition. Reports produced from an individual management system, such as a pavement management system (PMS), a bridge management system, or a sewer management system, can be combined to support reporting on all assets combined. A study was conducted to demonstrate the production of asset management reports by using a local agency PMS. The study was conducted by using the Metropolitan Transportation Commission PMS, which is used by many local agencies to support managing pavement networks of cities and counties. It is evident from the study that several useful reports supporting an overall asset management system can be created by using this PMS.
Assessing Impact of Bus Traffic on Pavement Maintenance Costs: City of Los Angeles
Authors: Shahin M. Y. , Crovetti James A. , Keifer Kurt A.
Published: April 2007

Engineers for the city of Los Angeles have observed that lanes carrying Mass Transit Authority (MTA) bus traffic deteriorate at a faster rate than similar lanes without bus traffic. The increased rate of deterioration results in greater maintenance costs in these lanes. To properly apportion the increased maintenance costs, city engineers need an objective method for quantifying the impact of MTA bus traffic. Multiple evaluation techniques are presented that may be used to quantify the effect of buses in terms of increased deterioration rates and greater rehabilitation costs. State-of-the-art techniques that use the results of deflection testing and pavement condition surveys are presented. Data collection procedures, methods for condition and structural analyses, and life-cycle costing procedures are provided. A case study that uses data collected from the city is presented. This study indicates an average yearly additional maintenance cost of $800 per lane-mile caused by MTA bus traffic, excluding associated costs for curb and gutter or maintenance hole adjustments.
Deficiency Analysis of As-Built Database to Enhance a Pavement Management System
Authors: Khan Riaz Ahmed , Helali Khaled , Jumikis Andris A. , He Zhiwei
Published: April 2007

The ability to systematically collect and record as-built data for pavement layers benefits highway departments in many aspects. A well-established database of as-built pavements provides a tool for maintaining an up-to-date corporate record of the physical pavement structures, keeping track of unit construction costs, and reducing the amount of pavement excavations during pavement investigations. A reliable as-built database also provides inputs for falling weight deflectometer analysis and calibrating pavement performance models in pavement management systems (PMSs). A task within the development of the second-generation PMS for the New Jersey Department of Transportation is to review and analyze the existing pavement as-built database for completeness and quality. A computer program was developed to scan and categorize the as-built data into five status levels: complete, partially complete—missing original construction data, partially complete—missing recent rehabilitation data, questionable data, and no data. The results of this analysis can be used to recommend improvement for the data-collection process and to guide further investigations, such as coring and ground penetration radar tests. The general approach used in the analysis is described, data status levels are defined, results for distribution of the pavement as-built data are provided, and the significance of the analysis for PMSs is discussed. Recommendations for improving completeness and quality of the pavement construction history database also are provided.
Crack Propagation in Portland Cement Concrete Beams: Implications for Pavement Design
Authors: loannides Anastasios M. , Sengupta Siddhartha
Published: April 2007

Hillerborg's fictitious crack model is used to simulate numerically progressive crack development in simply supported concrete beams. The tools used in the simulation are a general-purpose finite element package for the linear elastic aspects of structural response and specially coded iterative program CRACKIT for tracking crack propagation. Data generated in this manner are used to study the specimen-size effect, that is, the dependence of fracture behavior on geometric, boundary, and loading conditions. The numerical approach presented is used successfully to reproduce experimental and numerical results obtained by independent investigators. The main objective for the research is to examine how principles of similitude proposed in recent years and the experience gained in the application of dimensional analysis to concrete pavement data interpretation can aid in the formulation of more mechanistic-based failure criteria, which would eventually lead to improved pavement design procedures. Because of its similarity to conventional fatigue curves, a plot prepared by Gustafsson, of the normalized bending stress against the brittleness number, is found to deserve additional consideration as a possible candidate for this purpose.
Micromechanics Study on Top-Down Cracking
Authors: Wang L. B. , Myers L. A. , Mohammad L. N. , Fu Y. R.
Published: April 2007

Top-down cracking is a type of cracking that rivals the severity and prevalence of reflective cracking. It significantly reduces the pavement's quality service life. Yet the nature of top-down cracking has not been completely understood. Recent studies of the causes of top-down cracking have focused on identifying the mechanisms that induce tensile stresses at the surface by applying different combinations of surface tractions and the finite element method. Asphalt concrete is treated as a uniform linear elastic material. A new and different approach is presented for investigating the causes of top-down cracking by means of micromechanics. In this approach, asphalt concrete is viewed as a bonded granular material, and the microstructure, including aggregate particle configuration and mastic stiffness, is considered. Theories that predict the existence of tensile stress under compressive loading were reviewed. Both qualitative and quantitative experimental methods were developed to observe the location of top-down cracking and to measure the tensile strains in the pavement. The experimental results indicate the following: ( a) top-down cracking may initiate not only at the pavement surface but also at some distance down from the surface; ( b) both tensile-type and shear-type cracking could initiate top-down cracking; and ( c) top-down cracking may most likely initiate when the mastic is weaker or the pavement temperature is higher. Therefore, a mix sensitive to rutting may also be sensitive to cracking.
Calibration of Flexible Pavement Performance Equations for Minnesota Road Research Project
Authors: Timm David H. , Newcomb David E.
Published: April 2007

As mechanistic-empirical (M-E) pavement design gains wider acceptance as a viable design methodology, there is a critical need for a well-calibrated design system. Calibration of the pavement performance equations is essential to link pavement responses under load to observed field performance. A field calibration procedure for asphalt pavements that incorporates live traffic, environmental effects, observed performance, and in situ material characterization was developed. The procedure follows the M-E design process, iterating the transfer function coefficients until the performance equation accurately predicts pavement distress. Test sections from the Minnesota Road Research Project were used to demonstrate the calibration process, and fatigue and rutting performance equations were developed. It is recommended that further calibration studies be undertaken with this methodology, possibly by using sections from the Long-Term Pavement Performance project.
Current Status and Variability of In-Service Truck Tire Pressures in Texas
Authors: Wang Feng , Machemehl Randy B.
Published: April 2007

Truck tire pressure is closely related to tire-pavement contact pressure and could be an easy index representing the tire-pavement contact pressure level. To characterize in-service truck tire pressures and truck configurations on Texas highways, a truck survey was conducted on major Texas trucking routes. The survey data demonstrate a significant increase in in-service truck tire pressures in the state of Texas. Analysis of the collected tire-pressure data showed that factors such as axle weight, tire temperature, geographic area, highway class, traveled distance, and axle type are related to the in-service tire-pressure values. In a survey study, a factorial experiment design and a stratified sampling design were used. Analysis of variance, analysis of covariance, and t-tests were used for comparisons of truck tire-pressure data. Laboratory experiments and linear regression were used to identify relationships between the parameters of tire pressure and tire temperature. The survey results for in-service truck tire pressures and the comparisons and analyses of factors differentiating truck tire pressures are presented.
Comparison of As-Constructed and As-Designed Flexible Pavement Layer Thicknesses
Authors: Mladenovic Goran , Jiang Y. Jane , Selezneva Olga , Aref Susanne , Darter Michael
Published: April 2007

Sound pavement design is important for improving pavement performance, but construction is equally critical. Because of variations in pavement construction, the as-constructed pavement layer thickness varies spatially within a pavement section, and the mean constructed pavement layer thickness often deviates from the designed values. The as-constructed pavement layer thicknesses are compared to their design values by using data from the newly constructed flexible pavement sections in the Long-Term Pavement Performance program. First, the distribution type of the mean layer thickness deviation was investigated, and a combined statistical test for skewness and kurtosis showed that the mean thickness deviations may be assumed to be normally distributed for a given layer type and target thickness. Typical thickness deviation summary statistics values were derived to estimate the extent of deviations from the design thicknesses. Second, the analysis showed that elevation thickness data differ from the core examination data. Furthermore, as-constructed layer thickness values were compared to their design values by looking into the percentage of the individual measurements falling into specified ranges from the design values and by using two-sided and one-sided t-tests to compare the mean constructed thicknesses and the design values. The analyses showed that the mean constructed layer thicknesses tend to be above the design value for the thinner layers and below the design value for the thicker layers for the same layer and material type. Results from the study will be useful as inputs for reliability-based design procedures.
Analysis of Trip and Stop Duration for Shopping Activities: Simultaneous Hazard Duration Model System
Authors: Srinivasan Karthik K. , Guo Zhiyong
Published: April 2007

A joint hazard-based model for the analysis of simultaneous (mutually interdependent) duration processes is proposed. The proposed model generalizes independent hazard-based models by accounting for correlations between simultaneous duration processes. Furthermore, the model also permits the use of flexible and variable hazard function parameters to capture realistic features observed empirically in activity duration data (e.g., bimodal peaks). To account for correlated processes (duration processes) that underlie observed stop and trip durations, the proposed model relies on an implicit component of error structure that combines a baseline hazard function (log–logistic distribution) with a mixing (log–normal) distribution. This model is estimated by the simulated maximum-likelihood technique and is used to analyze activity and trip duration for shopping activities. The results highlight the need to account for duration dependence effects in activity–travel durations. Furthermore, hazard-based models that disregard correlation across joint duration processes can provide biased estimates and inaccurate forecasts. Empirical results from San Francisco, California (1996), activity diary data imply that stop and trip durations for shopping activities are positively correlated. The hazard rate profile (shape and intensity) also varies significantly across individuals, suggesting the need for targeted demand management measures. At a substantive level, the results indicate the role of personal, household, and situational attributes on activity and trip duration decisions. These findings and models have important applications in the analysis of activity–travel dimensions of duration and timing and the evaluation of alternate travel demand management measures.
Attitudinal Market Segmentation Approach to Mode Choice and Ridership Forecasting: Structural Equation Modeling
Authors: Outwater Maren L. , Castleberry Steve , Shiftan Yoram , Ben-Akiva Moshe , Shuang Zhou Yu , Kuppam Arun
Published: April 2007

The San Francisco Bay Area Water Transit Authority is evaluating expanded ferry service, as required by the California Legislature. As part of this process, Cambridge Systematics developed forecasts using a combination of market research strategies and the addition of nontraditional variables into the mode choice modeling process. The focus of this work was on expanding the mode choice model to recognize travelers' attitudes and different market segments. Structural equation modeling was used to simultaneously identify the attitudes of travel behaviors and the causal relationships between traveler's socioeconomic profile and traveler attitudes. Six attitudinal factors were extracted, and three of these were used to partition the ferry-riding market into eight segments. These market segments were used to estimate stated preference mode choice models for 14 alternative modes, which separated the travelers' reactions to time savings by market segment and which recognized that mode choices are different for market segments that are sensitive to travel stress or the desire to help the environment. The new mode choice models were applied within the framework of the Metropolitan Transportation Commission's regional travel model and calibrated to match modal shares, modes of access to each ferry terminal, ridership by route and time period, and person trips by mode at screening line crossings. Additional validation tests of significant changes in ferry service in recent years were used to confirm the reasonableness of the stated preference model. The model has been applied for three future year alternatives and to test the sensitivities of pricing, service changes, and alternative transit modes.
Analysis of Elderly Mobility by Structural Equation Modeling
Authors: Kim Sungyop
Published: April 2007

Mobility is a critical element of quality of life. This is as true for the elderly population as for the larger population. The elderly often have limited physical abilities and financial constraints that might reduce their mobility. Helping the growing elderly population to maintain decent mobility is a critical challenge for transportation planning and policy. For this, the factors that influence the mobility of the elderly population (elderly mobility) must be understood. Only a few systematic studies, however, have been published. Descriptive statistics of the potentially influential factors make it difficult to assess their effects on elderly mobility. The transportation mobility of retired people age 65 years or older in the Puget Sound region of Washington State was analyzed by using a structural equation model. The statistical significance and relative effects of various personal and household characteristics and urban form on elderly mobility were tested. The structural equation model finds statistically significant relationships between age, gender, transportation disability, possession of a driver's license, and education level and elderly mobility. Among these variables, age and education level show the strongest effects. Urban form, however, seems to be insignificant.
Formulation and Solution Algorithm for Fuzzy Dynamic Traffic Assignment Model
Authors: Liu Henry X. , Ban Xuegang , Ran Bin , Mirchandani Pitu
Published: April 2007

An issue that is always important in the development of traffic assignment models is how travelers' perceptions of travel time should be modeled. Because travelers rarely have perfect knowledge of the road network or of the travel conditions, they choose routes on the basis of their perceived travel times. Traditionally, travelers' perceived travel times are treated as random variables, leading to the stochastic traffic assignment problem. However, uncertain factors are also observed in the subjective recognition of travel times by travelers, and these can be illustrated as fuzzy variables. Therefore, a fuzzy dynamic traffic assignment model that takes into account the imprecision and the uncertainties in the route choice process is proposed. By modeling the expressions of perceived travel times as fuzzy variables, this model makes possible the description of a traveler's process of choosing a route that is more accurate and realistic than those from its deterministic or stochastic counter parts. The fuzzy perceived link travel time and fuzzy perceived path travel time are defined, and a fuzzy shortest path algorithm is used to find the group of fuzzy shortest paths and to assign traffic to each of them by using the so-called C-logit method. The results of the proposed model are also compared with those from the stochastic dynamic traffic assignment model, and it is demonstrated that the impact of advanced traveler information systems on the traveler's route choice process can be readily incorporated into the proposed model.
Modeling the Choice to Use Toll and High-Occupancy Vehicle Facilities
Authors: Erhardt Gregory D. , Koppelman Frank S. , Freedman Joel , Davidson William A. , Mullins Andrew
Published: April 2007

Traditionally, mode choice models distinguish between drive-alone and shared ride modes, leaving the network assignment models to predict the assignment of vehicles to toll and high-occupancy vehicle (HOV) facilities. If the shortest generalized cost path in the user equilibrium assignment is a toll or HOV path, the trip becomes a toll or HOV trip. Mode choice models that include the use of general-purpose highways, toll roads, and HOV lanes simultaneously with the choice of the drive-alone and shared ride modes are developed. Multinomial logit and nested logit models are estimated for this full set of alternatives. The models are estimated from a sample of data enriched by special surveys of toll, HOV, and transit users in the Houston, Texas, region. These data provide an empirical basis for studying the behaviors of toll and HOV facility users that is not normally available. The results indicate that the time saved by using these facilities has a higher utility weight than the time differences between other modes. Furthermore, for each mile traveled on a toll or HOV facility, there is an additional benefit that is partially offset by any excess in total travel distance necessary to use the toll or HOV facility. The additional preference for toll and HOV facilities can be explained by a perception of lower travel time, less driving stress, and higher reliability on these facilities. These results suggest that selection of a least-cost path in trip assignment is not sufficient for modeling the use of toll and HOV facilities.
Long Transport Chains: Exporting from a Peripheral Island
Authors: Finlay Hugh , O’Mahony Margaret , O’Sullivan Donal
Published: April 2007

The crucial dependence on intermodal transport of an open island economy, where almost all external trade passes through the seaports, is examined. The rapid growth of the Irish economy puts great strains on the transport supply chains, particularly in the vicinity of the principal seaport in Dublin, where major congestion occurs. This adversely affects the competitiveness of small and medium-sized exporting companies. Increasing prosperity has resulted in an explosion in the numbers of private cars, which puts great strain on an inadequate internal infrastructure. A review of Irish ports confirms that congestion on the access routes to the Dublin port is the major bottleneck in the long transport chains for exporters. Relief from the freight traffic transiting the city center must await the completion of a dedicated port access tunnel, and interim solutions are needed. In the case of food exporters, globalization, the power of the retail conglomerates, and peripheral location demand a high level of supply chain efficiencies. A survey of export transport chains for selected products shows that transit costs can be a significant proportion of the total consignment value. At the level of the indigenous companies, supply chain management capabilities are shown to be below an acceptable standard in two-thirds of the firms surveyed. Possible solutions for facilitation of freight access in the vicinity of the port and for introduction of more sustainable solutions for goods deliveries in the historic city center are explored. Measures that can be taken to improve the logistics management capabilities in companies are also described.
Framework for Study of Carrier Strategies in Auction-Based Transportation Marketplace
Authors: Andres Figliozzi Miguel , Mahmassani Hani S. , Jaillet Patrick
Published: April 2007

Online markets for transportation services in the form of Internet sites that dynamically match shipments (shippers' demand) and transportation capacity (carriers' offer) through auction mechanisms are changing the traditional structure of transportation markets. A general framework for the study of carriers' strategies in a transportation auction market place is provided. The unique characteristics of these marketplaces and the sources of difficulty in analyzing the performance of these market places under different carrier bidding strategies are discussed. A simulation framework is used to explore the complex engineering and economic processes and issues that arise in a transportation marketplace and that are difficult to explore by using standard analytical or statistical tools. Some results and the overall simulation framework are also discussed.
Application of Adaptive Neuro-Fuzzy Inference System to Analysis of Travel Behavior
Authors: Prˇibyl Ondrˇej , Goulias Konstadinos G.
Published: April 2007

A relatively new method for data analysis called the adaptive neuro-fuzzy inference system (ANFIS) is illustrated with an example from travel behavior modeling. The options offered by this data analysis technique are illustrated by using data from Australia. In addition, an experiment was performed to identify the optimal split of data into an estimation sample and a validation sample. Comparisons of ANFIS and the more traditional regression methods such as ordinary least-squares linear regression and negative binomial regression were performed by using the mean square error and correlation coefficients. ANFIS is shown to be a useful tool, and its further use in travel behavior research and applications in transportation planning is recommended. However, many additional issues require further scrutiny and experimentation, which are discussed.
Developing a Commodity Flow Database from Transearch Data
Authors: Ahanotu Dike N. , Fischer Michael J. , Louch Hugh W.
Published: April 2007

A procedure is described for analyzing Reebie Transearch data to create a commodity flow database that is useful for transportation planning purposes. Several elements of the procedure were recently applied as part of the development of a commodity flow database for the Portland metropolitan area. The procedure begins with an overview of the robustness of various Transearch data elements. For less robust data elements, specific processes are described to improve on the Transearch data. This process generally includes acquiring additional data from federal and state agencies, acquiring additional information from primary industry sources, and applying these data to the geographic area of concern for the commodity flow database. A methodology for estimating the commodity distribution for goods movement that originates in warehouses and distribution centers is also described. Supplemental freight data sources are identified, and elements of these data sources that can be used to verify and refine the Transearch data are highlighted. In the case of discrepancies between the Transearch data and other freight data sources, a process is described to determine potential sources of the discrepancy and further improve on the Transearch data toward the creation of a full commodity flow database.
Development of a Hybrid Model for Dynamic Travel-Time Prediction
Authors: Kuchipudi Chandra Mouly , Chien Steven I. J.
Published: April 2007

Travel-time prediction has been an interesting research subject for decades, and various prediction models have been developed. A prediction model was derived by integrating path-based and link-based prediction models. Prediction results generated by the hybrid model and their accuracy are compared with those generated by the path-based and link-based models individually. The models were developed with real-time and historic data collected from the New York State Thruway by the Transportation Operations Coordinating Committee. In these models, the Kalman filtering algorithm is applied for travel-time prediction because of its significance in continuously updating the state variables as new observations. The experimental results reveal that the travel times predicted with the path-based model are better than those predicted with the link-based model during peak periods, and vice versa. The hybrid model derives results from the best model at a given time, thus optimizing the performance. A prototype prediction system was developed on the World Wide Web.
Application of Probe-Vehicle Data for Real-Time Traffic-State Estimation and Short-Term Travel-Time Prediction on a Freeway
Authors: Nanthawichit Chumchoke , Nakatsuji Takashi , Suzuki Hironori
Published: April 2007

Traffic information from probe vehicles has great potential for improving the estimation accuracy of traffic situations, especially where no traffic detector is installed. A method for dealing with probe data along with conventional detector data to estimate traffic states is proposed. The probe data were integrated into the observation equation of the Kalman filter, in which state equations are represented by a macroscopic traffic-flow model. Estimated states were updated with information from both stationary detectors and probe vehicles. The method was tested under several traffic conditions by using hypothetical data, giving considerably improved estimation results compared to those estimated without probe data. Finally, the application of the proposed method was extended to the estimation and short-term prediction of travel time. Travel times were obtained indirectly through the conversion of speeds estimated or predicted by the proposed method. Experimental results show that the performance of travel-time estimation or prediction is comparable to that of some existing methods.
Travel-Time Reliability as a Measure of Service
Authors: Chen Chao , Skabardonis Alexander , Varaiya Pravin
Published: April 2007

Statistics from a corridor along Interstate 5 in Los Angeles show that average travel time and travel-time variability are meaningful measures of freeway performance. Variability of travel time is an important measure of service quality for travelers. Travel time can be used to quantify the effect of incidents, and incident information can help reduce travel-time uncertainty. Predictability of travel time is a measure of the benefits of intelligent transportation systems. These measures differ from those defined in the Highway Capacity Manual and other aggregate measures of delay.
Simplex-Based Calibration of Traffic Microsimulation Models with Intelligent Transportation Systems Data
Authors: Kim Kyu-Ok , Rilett L. R.
Published: April 2007

In recent years, microsimulation has become increasingly important in transportation system modeling. A potential issue is whether these models adequately represent reality and whether enough data exist with which to calibrate these models. There has been rapid deployment of intelligent transportation system (ITS) technologies in most urban areas of North America in the last 10 years. While ITSs are developed primarily for real-time traffic operations, the data are typically archived and available for traffic microsimulation calibration. A methodology, based on the sequential simplex algorithm, that uses ITS data to calibrate microsimulation models is presented. The test bed is a 23-km section of Interstate 10 in Houston, Texas. Two microsimulation models, CORSIM and TRANSIMS, were calibrated for two different demand matrices and three periods (morning peak, evening peak, and off-peak). It was found for the morning peak that the simplex algorithm had better results then either the default values or a simple, manual calibration. As the level of congestion decreased, the effectiveness of the simplex approach also decreased, as compared with standard techniques.
Generating Vehicle-Specific Speed Profiles from Automatic Traffic Recorders
Authors: Meyer Eric
Published: April 2007

Conventional speed studies can be used to evaluate the effects of various aspects of highway design and traffic control on the speeds at which drivers choose to travel. Typical parameters examined are mean speeds, 85th percentile speeds, and speed variation indicated by standard deviation or mode. More detailed studies have been conducted by using manual techniques and specialized equipment to generate vehicle-specific speed profiles. A useful technique, called vehicle tracing, allows data from common automatic traffic recorders to be used to generate such profiles automatically. The availability of these profiles opens new avenues of analysis that ultimately promote safer highway design and traffic-control practices. This technique is discussed, and its benefits are illustrated through a case study—an evaluation of optical speed bars, an innovative technique for slowing traffic in highway work zones.
Collecting Vehicle-Speed Data by Using Time-Lapse Video Recording Equipment
Authors: Strong Christopher , Lowry Scott , McCarthy Peter
Published: April 2007

An innovative application of time-lapse video recording is used to assist in an evaluation of a highway safety improvement. The improvement is an icy-curve warning system near Fredonyer Summit in northern California that activates real-time motorist warnings via extinguishable message signs, based on weather readings collected from road weather information systems. A measure of effectiveness is whether motorist speed is reduced as a result of real-time warnings to drivers. Why indirect speed measurement with video was preferred over radar for this case is discussed, as is how specific methodological issues related to the custom-built equipment, including camera location and orientation, distance benchmarking, and data collection and reduction. Theoretical and empirical accuracy measurements show that the video surveillance trailers yield results comparable to radar and, hence, would be applicable for studies in which speed change is measured. Because this particular technology had not been used previously, several lessons are documented that may help determine where and how similar equipment may be optimally used in future studies.
Web-Based Rural Road Asset-Management System
Authors: Herabat Pannapa , Satirasetthavee Dussadee , Amekudzi Adjo
Published: April 2007

The Department of Accelerated Rural Development in Thailand has undergone major structural reforms according to the direction of National Economic and Social Development Plan 9, which decentralizes government authority into subdistrict levels. The goals for subdistrict level management are to improve the quality of life and the living standard through economic and social development in rural areas. By restructuring the maintenance practice and policy to complement the new orientation of the plan and to enable the proper planning of rural road asset maintenance activities, a systematic rural road asset-management system was implemented to achieve the goal of the subdistrict and central management. A web-based technology was used to provide an easy linkage between the central and the remote offices for both network and project-level management. The organizational barriers, development process, tools and technology, data integration, and benefits of the improved data-management system are discussed. The developed system includes data regarding pavement, bridge, drainage system, traffic sign, pavement marking, and vegetation problems. How web-based information technology can be applied to an asset-management system is discussed. The benefits are measured for productivity, profitability, and rural road user effects.
Temporal Variability of Car Use as an Input to Design of Before and After Surveys
Authors: Richardson A. J.
Published: April 2007

Before and after surveys are a common method for measuring the effect of specific policies and projects designed to cause changes in travel behavior. Design issues of before and after surveys used to evaluate projects designed to change travel behavior are addressed. A quantitative understanding of the underlying variability of the parameters to be measured was needed—in particular, the variation over time in car travel by individuals and households. Since no data were available locally, a detailed analysis was made of the 6-week travel diaries from the MobiDrive survey conducted in Germany to estimate the coefficients of variation in key travel parameters. These results were then adapted for use in the presented project. Several features emerged from this analysis. First, in general, larger sample sizes are needed to detect changes in either distance traveled or travel time than for trips undertaken. Second, larger sample sizes are needed to detect changes from repeated cross-sectional surveys than from a panel survey. Third, larger sample sizes are needed to detect changes when using a daily travel diary, compared with use of a weekly travel diary (although this difference can be substantially reduced in a panel survey by maintaining the same day of the week for each household in later waves of the panel). Finally, larger sample sizes are needed to detect changes from person travel data than from household travel data. However, some of the design parameters that allow smaller sample sizes also make the survey more difficult to conduct.