Showing papers in "Journal of Transportation Engineering-asce in 1995"

Short-Term Prediction of Traffic Volume in Urban Arterials

Abstract: This paper attempts to develop time-series models for forecasting traffic volume in urban arterials. The Box-Jenkins approach is used to estimate the time-series models. A 1-min data set representing traffic volume on five major urban arterials were available to estimate time-series models. The Box-Jenkins autoregressive integrated moving average (ARIMA) model of order (0, 1, 1) turned out to be the most adequate model in reproducing all original time series. The developed model is easy to understand and implement. Further, the model is computationally tractable, and only requires the storage of the last forecasted error and current traffic observation.

Poisson Regression Models of Infrastructure Transition Probabilities

Abstract: Markovian transition probabilities have been used extensively in the field of infrastructure management, to provide forecasts of facility conditions. However, existing approaches used to estimate these transition probabilities from inspection data are mostly ad hoc and suffer from several statistical limitations. In this paper, econometric methods for the estimation of infrastructure deterioration models and associated transition probabilities from inspection data are presented. The first method is based on the Poisson regression model and follows directly from the Markovian behavior of infrastructure deterioration. The negative binomial regression, a generalization of the Poisson model that relaxes the assumption of equality of mean and variance, is also presented. An empirical case study, using a bridge inspection data set from Indiana, demonstrates the capabilities of the two methods.

Optimal Scheduling of Urban Transit Systems Using Genetic Algorithms

Abstract: Scheduling of urban transit network can be formulated as an optimization problem of minimizing the overall transfer time (TT) of transferring passengers and initial waiting time (IWT) of the passengers waiting to board a bus/train at their point of origin. In this paper, a mathematical programming (MP) formulation of the scheduling problem at one transfer station is presented. The MP problem is large and nonlinear in terms of the decision variables, thereby making it difficult for classical programming techniques to solve the problem. We apply genetic algorithms (GAs)-search and optimization methods based on natural genetics and selection-to solve the scheduling problem. The main advantage of using GAs is that the problem can be reformulated in a manner that is computationally more efficient than the original problem. Further, the coding aspect of GAs inherently takes care of most of the constraints associated with the scheduling problem. Results from a number of test problems demonstrate that the GAs are able to find optimal schedules with a reasonable computational resource. The paper concludes by presenting a number of extensions to the present problem and discusses plausible solution techniques using GAs. The success of GAs in this paper suggests their efficacy as a solution tool for similar optimization problems arising in transportation systems.

Airport choice in multiple-airport regions

Abstract: A logistic model is constructed to predict airport choice in a multiple-airport region and estimated using passenger data from the Washington, D.C./Baltimore area. In agreement with previous work, it was found that airport access time and flight frequencies were significant predictors of airport choice, although, as might be expected, decreased access time and additional flight frequencies were more important to the business traveler than to the nonbusiness traveler. Additional estimations indicated that when only those passengers within reasonable proximity of more than one airport were included in the estimation, the significance of access time decreased and that of flight frequencies increased. Additional variables for a passenger's experience with an airport were then included in the model and were significant. This would indicate that passengers who have used an airport will tend to continue to use the same airport, all other factors being equal.

Model to Reduce Airline Schedule Disturbances

Abstract: A wide variety of factors result in disturbances in carrying out planned airline schedules. Technical failures in the aircraft, meteorological conditions, crew delay, crews not showing up for flights, breakdowns in aircraft ground servicing equipment, and bottlenecks at airports lead to cancelation and/or delay of some flights. This paper develops a model to reduce airline schedule disturbances. The heuristic model that is developed [using the first in, first out (FIFO) principle and a sequential approach based on dynamic programming] can greatly facilitate the work of the dispatcher when making decisions regarding traffic management. The developed models and corresponding software package were tested on a large number of hypothetical numerical examples. The software package provides the dispatcher with an active role in choosing the final solution. Relying on his or her experience and intuition, the dispatcher can change the type of aircraft on a specific flight, departure times of individual flights, or...

Viscoelastic approach to rutting in flexible pavements

Abstract: Permanent deformation (rutting) in bituminous pavements is treated as a linear viscoelastic flow phenomenon and is calculated using the linear elastic layered pavement model VESYS, reported by Kenis in 1978, supplied with equivalent viscous material properties. After an initial compaction period, the model predicts that the permanent deformation per wheel pass is proportional to the static axle load and inversely proportional to the vehicle speed. The predicted permanent deformation field is realistic and independent of the material elasticity. To determine the viscosity of asphalt mixtures operating under a wide range of environmental conditions, a simple new theoretical method is introduced which is based on routine test data and requires only one parameter to be fitted to experimental data. Published wheel-tracking tests were used to determine this parameter. Rut depth predictions are compared with experimental data from a recent full-scale test in France. Agreement is generally good, indicating the applicability of this linear rutting model.

Development of No-Fines Concrete Pavement Applications

Abstract: No-fines concrete is a type of concrete from which the fine aggregate is totally omitted and single-sized coarse aggregates are held together by a binder consisting of a paste of hydraulic cement and water. The earliest application of no-fines concrete dates back to 1852 when two houses and a seagroin of 61 m (200 ft.) long and 2.15 m (7 ft.) high were constructed in the United Kingdom. Its extensive use came about after World War II when nearly the whole of Europe was in vast housing need. The unprecedented demand for bricks, and the subsequent inability of the brick-making industry to provide bricks in sufficient quantity, led to the adoption of no-fines concrete as a construction material since it required considerably less cement per volume than conventional concrete. Earlier use of no-fines concrete was confined to building construction and other nonpavement applications. The present paper cites the use of no-fines concrete for pavement applications in the United States and Europe.

Identifying Accident-Prone Locations Using Fuzzy Pattern Recognition

Abstract: This paper describes a method to identify accident-prone locations (APLs) based on an assessment of factors that contribute to accidents. Current methods to identify APLs make no distinction between accidents that result from road- and nonroad-related factors. Combining accidents that are treatable and nontreatable by road improvements can be misleading and may lead to a misallocation of funds by road authorities. This paper presents a computerized procedure that uses safety experts' knowledge on classifying accidents into a finite set of categories. In practice, the categories can include any one or a combination of the three basic highway system components: the driver, the vehicle, and the road environment. Realizing the complex interaction of these components within the accident environment, the procedure employs fuzzy pattern recognition techniques for the classification process. Accidents that do not belong to the road environment category are excluded from the identification of APLs. The method is tested using data from the accident database of the British Columbia Ministry of Transportation and Highways. The method and results are described.

Investigation of bonding between asphalt layers on road construction

Abstract: Bonding of asphalt layers on road construction is usually examined with the pull-off test, measuring the adhesive power. This value however, is not appropriate to characterize the fracture-mechanical behavior of layer bondings and is thus inappropriate to be introduced into fracture-mechanical finite-element simulations. Therefore a simple procedure for measuring the fracture-mechanical behavior of layer bondings has been developed in this study. Cubic or cylindrical specimens (with their interface in their middle and a starter notch in the interface) are split under stable crack growth conditions. During testing, the complete load-displacement curve is determined until final fracturing of the bonding takes place. The load-displacement curve characterizes the mechanical behavior of the material bonding in the crack opening mode and is an important basis for a numerical treatment of interface problems. Results obtained with this new measuring procedure are presented and discussed. As an example, propagatio...

Analysis and Verification of Thermal-Gradient Effects on Concrete Pavement

Abstract: An experimental and analytical study was conducted to develop an effective method for determining realistic thermal-load induced stresses in concrete pavements. Temperatures throughout the concrete slabs were measured over an extended time period. Resulting critical stresses were then analytically derived following the procedure developed in this study. To verify these analytical stresses, load-induced strains and deflections were recorded at numerous locations on the test slab at various time periods, using the falling weight deflectometer as a loading device. The findings confirmed the importance and the need to account for the thermal gradient in the design and analysis of concrete pavements. The temperature data indicated that the temperature distributions were mostly nonlinear and can be represented fairly well by a quadratic equation. In addition, theoretical analysis of the induced stresses suggests the consideration of the total temperature distribution throughout the concrete slab depth rather th...

Random Field Modeling of Railway Track Irregularities

Abstract: Track irregularity is considerably important in track-vehicle studies. Recorded data of these irregularities form a basis to develop track standards. This also helps specify track inputs to the vehicles. In this paper random field models for vertical irregularity data obtained from Indian railways has been presented. It is shown that irregularity in the vertical profile can be modeled as stationary Gaussian random field, which can be defined in terms of the power spectral density (PSD) function. Such a model can predict the values of peak amplitudes in a given track length. Further, the absolute vertical profile of the left and right rails belong to the isotropic random field. The implication of this in describing the input matrix of multiaxle vehicles is discussed.

Component Dowel-Bar Model for Load-Transfer Systems in PCC Pavements

Abstract: A component dowel-bar model has been developed to simulate the doweled joint in portland-cement-concrete (PCC) pavements. The model consists of two bending beams of finite length, embedded in concrete, connected by a shear-bending beam. The objective is to model the dowel-bar load-transfer mechanism in PCC pavements. The new model can appropriately consider the interaction between concrete and embedded dowels. The model allows a rigorous numerical analysis without an increased number of unknowns. The model can be integrated into a finite-element program to predict the responses of the load transfer system, including distributions of bending moment, shear force and bearing stress of each dowel without using the assumption of effective length. A comparison between experimental and analytical results has verified that the component model can be used to reasonably predict the responses of a dowel bar load transfer system.

Comparative Assessment of AHP and MAV in Highway Planning: Case Study

Abstract: A comparative analysis is made between the analytic hierarchy process (AHP) and the multiattribute value (MAV) functions, using the MAV theory as the basis of reference, in the evaluation of transportation projects. The analysis considers three different perspectives: theoretical support, practicality, and ability to capture the decision maker's (DM) preferences. From the theoretic-behavioral standpoint, it appears that the validity of some of the assumptions of the AHP remain to be formally established, as concluded by several researchers. Secondly, the practicality of AHP was analyzed, in terms of the quantity and type of information demanded from the DM. For an even mix of ratio scale variables and nonratio scale variables the AHP requires less information than the MAV, provided the number of alternatives is less than five. Beyond this limit, the AHP requires more information than MAV. The ability to capture the decision maker's preference structure is analyzed through a case study, to which both metho...

Classifying highways: hierarchical grouping versus kohonen neural networks

Abstract: Neural networks may be useful alternatives for statistical classification techniques when the available data is incomplete. This paper discusses the results obtained from a statistical technique called hierarchical grouping and the Kohonen neural network for classifying traffic patterns. The Kohonen neural network is shown to be a reasonable approximation of the hierarchical-grouping technique. It is suggested that hierarchical grouping of a small sample of typical traffic patterns may be a useful first step in setting up a Kohonen neural network for traffic-pattern classification. The Kohonen neural network can be used for classifying a large number of complete as well as incomplete traffic patterns as they become available. The neural network can also adapt the classification process to the change in the typical traffic patterns over time.

Use of nonlinear subgrade modulus in AASHTO design procedure

Abstract: Resilient modulus ( M r ) of subgrade is a very important factor in the pavement design and evaluation process. Typically, this factor is evaluated using simple empirical (non–stress-dependent) relationships with CBR (California-bearing-ratio) values as defined by several agencies. However, with the current state of knowledge, it is evident that the response of typical unbound subgrade materials may be nonlinear and hence, a function of the state of stress. Because of this material's stress dependency, different pavement cross sections (due to change in layer thickness) and/or layer moduli will cause a change in the M r response of the subgrade material under given moisture-density conditions. Three approaches are presented in this paper to estimate the nonlinear resilient modulus response of fine grained soils to be used in the flexible design procedure from the American Association of State Highway and Transportation Officials (AASHTO). These approaches are based on stress-dependent Lotfi and Moossazade...

Effect of Heterogeneity of Traffic on Delay at Signalized Intersections

Abstract: The average delay caused to vehicles at signalized intersections is an important criterion in the evaluation of performance at these intersections. Various models have been developed to estimate delay to traffic at signalized intersections. All the models are based on homogeneous traffic conditions; these models may not estimate the delays satisfactorily under heterogeneous traffic conditions. A probabilistic approach based on first-order second-moment method has been adopted to estimate the saturation flow and the delay caused to traffic, at signalized intersections, under heterogeneous traffic conditions. Here, the interaction between the different types of vehicles are incorporated in the modified 1958 Webster model by considering the intercorrelation between different vehicle groups. The input data required for these models and the data required to validate the calculated values were collected by conducting extensive traffic surveys. Results showed that the delay estimated using the probabilistic approach was close to the observed values of delay.

Steel Pipe Wrinkling due to Longitudinal Permanent Ground Deformation

Abstract: The behavior and design of a straight buried steel pipe subject to permanent ground deformation (PGD) where the movement is parallel to the pipe axis is considered. The PGD zone is characterized by the amount of movement, δ, and the length or spatial extent, L , of the zone. Because of the ability of steel pipe to deform in tension well beyond the effective yield strain, wrinkling of the pipe wall in compression is taken as the failure mode of interest. Critical values for δ and L , which result in wrinkling of the pipe wall in compression are determined for five different pipe materials and various burial conditions. In most situations, it is found that the behavior and onset of wrinkling are governed by the length of the PGD zone. The utility of this information is illustrated by a design example.

Network design effects of dynamic traffic assignment

Abstract: This paper examines the effects of dynamic user-equilibrium (DUE) traffic assignment with scheduled trip arrival times on network design outcomes in comparison to outcomes with steady-state travel demands. The objective is to minimize systemwide travel cost by considering alternative link improvements to an existing network (e.g., select among budget-constrained subsets of link-improvement candidates). DUE is a temporal generalization of static user-equilibrium (SUE) assignment with additional constraints to insure temporally continuous trip paths and first-in first-out (FIFO) trip ordering between all origin-destination pairs. Previous research has not investigated the effects of dynamic travel demands and schedule delay (i.e., shifts by trips to earlier or later arrival times) on network design with multiple trip origins and destinations. DUE is formulated as a bilevel program of two subproblems solved successively by an iterative algorithm that consistently converges to solutions that closely satisfy t...

Vehicle and Pedestrian Accident Models for Median Locations

Abstract: It has long been recognized that medians are an effective method of increasing vehicular safety and capacity on urban and suburban arterials. Medians can provide an additional lane for through traffic by removing left turning vehicles from the traffic stream. Medians are also generally considered to be beneficial to pedestrian safety and operations. A number of studies have been conducted on modeling the expected number of vehicle accidents, and, hence, incremental benefits resulting from the installation of different median types. These studies did not, however, determine the expected pedestrian benefits resulting from the installation of medians. This paper presents the results of a study conducted for the Federal Highway Administration. It presents the activities and results of developing accident predictive equations for both vehicle-vehicle and pedestrian-vehicle accidents due to different median types. The model was developed for urban and suburban unlimited access arterials. The results are not applicable to rural environment or to limited access arterials.

Future of airline hubbed networks: some policy implications.

Abstract: By hubbing at a few airports, airlines can maintain high levels of aircraft utilization and take advantage of the economies of aircraft size. Passengers also benefit in the form of increased frequency of service. However, increased aircraft operations at major hubs imply certain diseconomies that include congestion delay, increased workload on air-traffic controllers, noise, and pollution. Using a network equilibrium model, this study attempts to project the future structure of domestic networks and to discuss some policy implications. The results suggest that network hubbing will continue to persist as an important feature of air transportation, but in a multihub system. Unless expanded substantially, major hubs will suffer from escalated levels of delays and will become mostly traffic-generator airports instead of connecting and transfer points. Some implications to the concept of wayports, hub pricing, and the role of aircraft technology in relieving delays at major hubs are also discussed.

Goal-programming methodology for integrating pavement and bridge programs

Abstract: A goal-programming methodology is presented for integrating the decisions involved in the development of annual pavement and bridge programs. The methodology involves four major steps: (1) identification of multiple objective functions with specific numerical goals; (2) assessment of the “importance” of each objective; (3) development of an assignment model that enables both project and network levels of integration; and (4) formulation of a goal program for optimal program development. Project-level integration is achieved by defining integrable highway units that constitute a bridge and adjacent pavement sections whose repair work can be implemented simultaneously. Network-level integration is achieved by defining objectives and constraints that link the decision variables corresponding to the entire population of pavement sections and bridges. The methodology has the advantage of capturing economies of scale and scope, and determines an optimal program that best achieves the goals. The results from the...

Rheological properties of rubber-modified asphalt

Abstract: The performance of rubber (from used tires) as an asphalt cement modifier was evaluated by performing experiments on the shear-flow properties and creep-rupture behavior of modified asphalt cements. Results indicate that various asphalt/rubber samples exhibit shear-thickening, Newtonian, and shear-thinning behavior depending on the shear rate. The shear viscosity, linear viscoelastic functions, elasticity, and creep resistance of asphalt cement increased with the addition of rubber. These increases indicate that the addition of rubber will improve the low temperature properties of asphalt cement, and that such modifications are necessary to reduce the tendency of asphaltic-paving materials to crack in cold climates and to increase the life cycle of the road.

Incorporating life-cycle costs in highway-bridge planning and design

Abstract: Many state departments of transportation employ life-cycle cost analysis in their highway bridge-management systems as a means of decision-making in maintenance, rehabilitation, and replacement. Life-cycle cost analysis is based on the concept of discounted cash-flow analysis. The authors of this technical paper present a brief review of current methods for life-cycle cost analysis implementation, and based on that review, identify key factors that influence life-cycle cost analysis. The value index model is introduced, which considers bridge age, condition rating, and cost--the most critical factors in the decision-making process. The value index parameter incorporates these variables for the optimization strategy. This allows rational decisions to be made regarding the type of work to be performed that best suits a bridge's needs within the appropriate constraints. The "objective function," or the function to be optimized, is written in terms of the key factors that control the decision-making process. The method is demonstrated in several case studies for highway bridges in Illinois. Also discussed is the significance of certain limits imposed on the key factors in the optimization process and the various options that can be selected within these limits. Although the proposed model is suggested for project-level analysis, it can be extended for use in a network-level analysis as well. This application, however, necessitates development of a separate allocation-of-fund process that in turn needs input from the bridge engineer and information on the individual bridges in the network in terms of their needs and priorities for rehabilitation, repair, or replacement.

Positive feedback model of multiple-airport systems

Abstract: A model for allocating passenger traffic in a multiple-airport system is proposed and tested The model treats the supply-side of the system as endogenous, and represents it implicity using the principle that as traffic using an airport increases, the airport becomes more attractive This positive feedback effect and the preferences of air travelers for airports near their trip terminus are argued to be the key factors determining the distribution of traffic in a multiple-airport system The model is applied to the San Francisco Bay Area, served by airports in Oakland, San Francisco, and San Jose A disaggregate logit airport-choice model, in which airport utility is a function of travel time to trip origin, airport enplanements, is estimated The calibrated choice model, combined with estimates of the distribution of trip origins, is used to calculate equilibrium market shares Comparison of equilibria with observed shares shows high correlation, particularly for larger markets, and for the San Francisco and Oakland airports

Pavement thickness design for no-fines concrete parking lots

Abstract: A uniformly graded coarse aggregate and a cement-water paste comprise no-fines concrete. No-fines concrete is beneficial in areas that receive frequent or excessive rainfall because of its excellent drainage properties. This paper discusses thickness design of no-fines concrete parking lot pavements. Based on its engineering properties, traffic conditions, and subgrade characteristics, a determination about thickness of no-fines concrete pavements is made. Two design procedures were used for the thickness evaluation of no-fines concrete parking lots--American Association of State Highway and Transportation Officials (AASHTO) and Port Cement Association (PCA). Laboratory results indicate that if proper proportioning and densification occurs, no-fines concrete can be successfully employed as a surface paving material for parking lots. The thickness design tables reveal that the PCA design procedure is more appropriate for thinner pavements, while AASHTO yields a more conservative outcome for thicker pavements. Both design methods offered similar thickness results for intermediate traffic categories.

Parametric study of factors affecting flexible-pavement performance

Abstract: A new whole–life pavement–performance model (WLPPM) that is capable of making deterministic pavement–damage predictions due to realistic traffic and environmental loading has been developed A vehicle simulation is used to generate dynamic tire forces that are a function of distance along the pavement These dynamic tire forces are then combined with the appropriate pavement primary–response influence functions to give primary–response histories at regularly spaced points along the pavement The primary–response histories are then transformed into an increment of damage at each point along the pavement due to a single vehicle pass, and the surface–roughness profile is updated This procedure is then repeated until pavement failure occurs Using the WLPPM, the performance of two classes of pavement are examined operating under climatic conditions typical of the United Kingdom It is concluded that both dynamic vehicle loads and asphalt–layer stiffness variations can significantly influence long–term flexible–pavement performance

Development of effective rockfall barriers

Abstract: As a part of the construction of Interstate 70 through Glenwood Canyon, in Colorado, three new types of barriers for protection against rockfall were developed through a program of prototype testing, numerical simulation of rockfall events, and analysis of barrier response to impact by boulders. New barriers include a suspended pendulum system that attenuates the kinetic energy of falling boulders, a flexibly mounted fence of steel cables and mesh, and a free-standing mechanically stabilized earth wall. The capacity of rockfall barriers, stated as a limiting translational kinetic energy of falling boulders, ranges from 41 kJ (30,000 fts˙lb) for light fences to more than 1,400 kJ (1,000,000 fts˙lb) for mechanically stabilized earth walls. Earth walls can halt falling boulders that weigh as much as 13,700 kg (30,100 lb). The three barriers reported here are useful as options to ditches, berms, rigid fences, and rigid walls of rockfall protection for highways. This paper provides a summary of barriers develo...

Evidence on Transferability of Trip-Generation Models

Abstract: Full and partial transfer results of trip-production models among intercity, intracity, and intraregional locations are reported in this paper. Nineteen models were transferred 208 times among the locations. The variety of transfer conditions and number of transfers permitted inferences to be drawn on the conditions influencing transferability. It was observed that the quality of local data seriously affects the ability to discern transferability, and may account for the variable results observed in the literature. It was also observed that model quality and income affect transferability. For all transfers conducted in this study, the transferred models explained an average of 57% of the variation in trip-making behavior explained by locally estimated models. When locally estimated constants were used to replace transferred constants in the model, the transfer models explained, on average, 87% of the variation in trip-making behavior explained by locally estimated models. It was concluded that the adjustment of transfer-model parameters with local information (partial transfer) has the potential to improve transferability to such an extent that the need to predict transferability becomes redundant.

Contact-element model for dynamic analysis of jointed concrete pavements

Abstract: A finite-element algorithm is developed to analyze the dynamic response of multiple, jointed concrete pavements to moving aircraft loads. In the finite-element idealization, the pavement-subgrade system is idealized by thin-plate finite elements resting on a Winkler-type viscoelastic foundation represented by a series of distributed springs and dashpots. The dowel bars at the transverse joints are represented by plane frame elements. The dowel-pavement interaction effects are accounted for by employing contact elements between the pavement and the dowel bar. Keyed joint or aggregate interlock joint is assumed for the longitudinal joint and is represented by vertical spring elements. The dynamic aircraft-pavement interaction effects are considered in the analysis by modeling the aircraft by masses supported by spring-dashpot systems representing the landing gear of the aircraft. The accuracy of the computer code developed is verified by the available experimental and analytical solutions. A parametric study is conducted to investigate the effects of various parameters on the dynamic response of pavements.

Effects of routine maintenance on flexible pavement condition. discussion

Abstract: A discussion of a paper with the aforementioned title by Al-Mansour, Sinha, and Kuczek, published in this journal (Volume 120, Number 1, January/February 1994), is presented. The discussion focuses on the use of roughness-progression profiles as a means of selecting routine maintenance options. Fekpe asserts that the relationship between maintenance and pavement performance as measured by roughness modeling is weak, adding that sufficient detail is lacking in both the statistical analysis and discussions. No closure is offered by the authors.