Showing papers in "Journal of Transportation Engineering-asce in 1997"
TL;DR: This research effort focused on developing traffic volume forecasting models for two sites on Northern Virginia's Capital Beltway, and found that the nonparametric regression model was easy to implement, and proved to be portable, performing well at two distinct sties.
Abstract: The capability to forecast traffic volume in an operational setting has been identified as a critical need for intelligent transportation systems (ITS). In particular, traffic volume forecasts will support proactive, dynamic traffic control. However, previous attempts to develop traffic volume forecasting models have met with limited success. This research effort focused on developing traffic volume forecasting models for two sites on Northern Virginia's Capital Beltway. Four models were developed and tested for the freeway traffic flow forecasting problem, which is defined as estimating traffic flow 15 minutes into the future. They were the historical average, time-series, neural network, and nonparametric regression models. The nonparametric regression model significantly outperformed the other models. A Wilcoxon signed-rank test revealed that the nonparametric regression model was easy to implement, and proved to be portable, performing well at two distinct sties. Based on its success, research is ongoing to refine the nonparametric regression model and to extend it to produce multiple interval forecasts.
566 citations
TL;DR: Two statistical models for estimating incident delay and a model for predicting incident duration are provided that showed that up to 85% of variation in incident delay can be explained by incident duration, number of lanes affected,Number of vehicles involved, and traffic demand before the incident.
Abstract: Traffic congestion is a major operational problem on urban freeways In the case of recurring congestion, travelers can plan their trips according to the expected occurrence and severity of recurring congestion However, nonrecurring congestion cannot be managed without real-time prediction Evaluating the efficiency of intelligent transportation systems (ITS) technologies in reducing incident effects requires developing models that can accurately predict incident duration along with the magnitude of nonrecurring congestion This paper provides two statistical models for estimating incident delay and a model for predicting incident duration The incident delay models showed that up to 85% of variation in incident delay can be explained by incident duration, number of lanes affected, number of vehicles involved, and traffic demand before the incident The incident duration prediction model showed that 81% of variation in incident duration can be predicted by number of lanes affected, number of vehicles involved, truck involvement, time of day, police response time, and weather condition These findings have implications for on-line applications within the context of advanced traveler information systems (ATIS)
247 citations
TL;DR: The incident data systems that have evolved in several urban areas, often in connection with freeway service patrols and incident response team activities, already provide a valuable nationwide data resource for understanding incident patterns and their variations but better national coordination of locally collected incident data would be helpful for addressing issues beyond the scope of the local concerns.
Abstract: This paper presents a new model that predicts the number of freeway incidents and associated delays based on general freeway segment characteristics, traffic volumes, and incident management procedures. The model is intended to be used in planning capacity-enhancing freeway improvements and incident management programs. Estimates of incident frequencies, severity, durations, and delays are provided for seven standard incident types, each of which represents a significant fraction of total unplanned incidents and has severity and/or duration characteristics substantially different from the others. In addition to describing the incident prediction model, the paper addresses the need for a coordinated national strategy for collecting incident data, with particular attention to urban freeways. It concludes that the incident data systems that have evolved in several urban areas, often in connection with freeway service patrols and incident response team activities, already provide a valuable nationwide data resource for understanding incident patterns and their variations. However, better national coordination of locally collected incident data would be helpful for addressing issues beyond the scope of the local concerns for which virtually all current systems were originally designed. Specific areas for improvement include the definitions of incident types, descriptions of incident locations (relative to both the length and breadth of the highway), and data recording the critical times during incidents such as when detection, response, and clearing occur. Language: en
129 citations
TL;DR: In this paper, two approaches based on nonlinear fracture mechanics, the compliance approach and the R-Curve approach, were used to evaluate the low-temperature fracture parameters of conventional asphalt concrete and asphalt-rubber mixture.
Abstract: Current failure criteria of asphalt pavements are either empirical or assume linear elastic material response and use a single load level to relate the number of load repetitions to fatigue failure. To better understand the crack propagation properties of asphalt pavements, laboratory tests and nonlinear analysis were performed to evaluate the low-temperature fracture parameters of conventional asphalt concrete and asphalt-rubber mixture. Two approaches based on nonlinear fracture mechanics, the compliance approach and the R-Curve approach, were used. Beam specimens were prepared with different binder contents and tested under three-point bending flexural conditions at two test temperatures. A closed-loop servohydraulic test system was used with the crack mouth opening as the control parameter. Nonlinear fracture parameters were obtained at different stages of crack propagation. Results show that the asphalt-rubber mixture has higher fracture toughness and consequently larger resistance to cracking than asphalt concrete. Also, the asphalt-rubber mixture is less sensitive to temperature than asphalt concrete. Increasing the binder content increased the toughness values for both asphalt concrete and asphalt-rubber mixture in most cases. The R-Curve approach provides a good measure of characterizing the fracture behavior of asphalt mixtures.
115 citations
TL;DR: A system of disaggregate models that accounts for the effect of intersection, driver, and traffic characteristics on gap acceptance for left-turn maneuvers at urban T-intersections controlled by stop signs on the minor roads shows that the distribution of critical gaps is influenced by driver socioeconomic characteristics, expected waiting time, time of day, and trip purpose.
Abstract: This paper develops a system of disaggregate models that accounts for the effect of intersection, driver, and traffic characteristics on gap acceptance for left-turn maneuvers at urban T-intersections controlled by stop signs on the minor roads. The waiting time for each driver is first modeled using the hazard function. The binary probit model is then used to find the drivers' probabilities of accepting or rejecting a gap. These probabilities are used to calculate the critical gaps of individual drivers. The expected waiting time is included in the model as an explanatory variable. A multiple regression model is used for predicting the intersection mean critical gap. To estimate the parameters of the models, disaggregate data were collected by observing and interviewing drivers at 15 urban T-intersections in the Greater Amman area. The results show that the distribution of critical gaps is influenced by driver socioeconomic characteristics, expected waiting time, time of day, and trip purpose. The mean c...
109 citations
TL;DR: In this article, the search procedure and optimization technique of the long-term maintenance cost of a network-level bridge system are presented using a genetic algorithm, where a population of maintenance strategies evolves from one generation to the next generation by applying the principles of natural selection and survival of the fittest.
Abstract: With the rapidly increasing requirements of bridge maintenance and the limited budget available for this maintenance, the cost optimization of long-term maintenance strategy considering the network-level bridge system under an allowable deterioration level is becoming an important problem. However, the total maintenance cost is a function of the number of bridges and their deterioration degrees, the planning period, and the maintenance methods. The selection of the optimization algorithm is important to get the optimal solution of this problem. In this research, using the bridge deck as an example, the search procedure and optimization technique of the long-term maintenance cost of a network-level bridge system are presented using a genetic algorithm. A population of maintenance strategies evolves from one generation to the next generation by applying the principles of natural selection and survival of the fittest. The feasibility of this method is demonstrated using a real-world example, and the results are compared with the conventional maintenance planning. In addition, several maintenance policies are suggested and compared.
89 citations
TL;DR: A simulation laboratory for performance evaluation and design refinement of dynamic traffic management systems, which provides a unique tool for evaluating integrated ATIS and ATMS applications in a computer-based laboratory environment.
Abstract: This paper presents a simulation laboratory for performance evaluation and design refinement of dynamic traffic management systems. The laboratory consists of four integrated components : (1) a traffic management simulator, which mimics the generation of route guidance and operations of traffic signals and signs ; (2) a traffic flow simulator, which models individual vehicle movements and drivers' route choice decisions in the presence of real-time traffic information ; (3) a surveillance system module, which collects real-time traffic data from sensors and probe vehicles in the simulated network ; and (4) a control device module, which implements control strategies and route guidance generated by the traffic management system under evaluation. The simulation laboratory has been implemented in C++ using object-oriented programming and a distributed environment. It features a graphical user interface that allows users to visualize the simulation process, including animation of vehicle movements, state of surveillance sensors, traffic signals, signs, and so on. This modeling system provides a unique tool for evaluating integrated ATIS and ATMS applications in a computer-based laboratory environment.
86 citations
TL;DR: Using probe travel time data from a set of signalized arterials, it is shown that a is positive for well-traveled signalized links, implying that the variance of the mean of travel times obtained from n probes for the same link over a fixed time period does not go to zero with increasing n.
Abstract: An important design issue relating to probe-based Advanced Traveler Information Systems (ATISs) and Advanced Traffic Management systems is the sample size of probes (or the number of link traversals by probe vehicles) per unit time used in order to obtain reliable network information in terms of link travel time estimates. The variance of the mean of travel times obtained from n probes for the same link over a fixed time period may be shown to be of the form a+b/n where a and b are link-specific parameters. Using probe travel time data from a set of signalized arterials, it is shown that a is positive for well-traveled signalized links. This implies that the variance does not go to zero with increasing n. Consequences of this fact for probe-based systems are explored. While the results presented are for a specific set of links, the authors argue that because of the nature of the underlying travel time process, the broad conclusions would not hold for most well-traveled links with signal control.
84 citations
TL;DR: This model is designed to optimize a grid transit system in a heterogeneous urban environment whose demand and supply characteristics may vary arbitrarily among adjacent zones.
Abstract: Current analytic models for optimizing urban transit systems tend to sacrifice geographic realism and detail in order to obtain their solutions. The model presented here shows how an optimization approach can be successful without oversimplifying the spatial characteristics and demand patterns of urban areas. This model is designed to optimize a grid transit system in a heterogeneous urban environment whose demand and supply characteristics may vary arbitrarily among adjacent zones. Network characteristics (route and station locations) and operating headways are found that minimize the total cost, including supplier and user costs. Irregular many-to-many demand patterns, zonal variations in route costs, and vehicle capacity constraints are considered in a sequential optimization process.
77 citations
TL;DR: A recent freeway congestion prediction study for the Washington Department of Transportation (WSDOT) found that the sum of storage rates over time, SumSR(t) for a freeway section was a better variable for determining the best upstream ramp metering rates than the storage rate for time interval t, SR(t), which is the current WSDOT criterion.
Abstract: A recent freeway congestion prediction study for the Washington Department of Transportation (WSDOT) found that the sum of storage rates over time, SumSR(t), for a freeway section was a better variable for determining the best upstream ramp metering rates than the storage rate for time interval t, SR(t), which is the current WSDOT criterion. (Use of the SumSR(t) variable for this purpose requires that the summation be started during a period of low density flows.) Another finding was that the SumSR(t) variable was a better detector of loop “chattering” errors than WSDOT's current criterion, which misses chattering errors that occur at normal traffic volume levels. Since calculation of SumSR(t) is easily incorporated in the current WSDOT ramp metering algorithm, the writer recommends its use in futute WSDOT freeway metering schemes.
69 citations
TL;DR: There seems to be a significant lack of empirical results and real-world applications that are needed in order to promote the transfer of this modeling approach from research to professional practice.
Abstract: This paper reviews a class of models that combine equilibrium traffic assignment and intersection control into a single analysis framework under the assumption of flow-responsive signal settings. The most significant feature of these models is their capacity to take into account explicitly the mutual interactions between signal control policies and user route choices; such interactions are usually disregarded both in ordinary traffic assignment models and in traditional traffic engineering practice. After defining the combined traffic assignment and control problem, and reviewing alternative formulations and solution algorithms, this paper discusses possible approaches to modeling the various types of link interactions that arise from the joint use of intersections by competing traffic movements. Important conceptual issues and implementation aspects are considered, and their potential policy implications are emphasized. The main conclusion of the survey is that, while the theoretical properties of combined traffic assignment and control models have been studied over the last two decades and are now well understood, there seems to be a significant lack of empirical results and real-world applications, that are needed in order to promote the transfer of this modeling approach from research to professional practice.
TL;DR: In this article, the relative effectiveness of commercially available road dust suppressants in abating fugitive dust emission and loss of fines from unpaved road surfaces was assessed in a field-based research project.
Abstract: The relative effectiveness of commercially available road dust suppressants in abating fugitive dust emission and loss of fines from unpaved road surfaces was assessed in a field-based research project. The dust suppressants studied, lignin derivatives and chloride based compounds, were used on unpaved road test sections during the severe dusty months of 1993 and 1994 in Colorado, which fell in the late spring to autumn period. To measure the relative effectiveness of the different dust suppressants, comparative fugitive dust emission studies were conducted on unpaved road test sections using the Colorado State University Dustometer, a dust-sampling device developed during this research. In addition, total aggregate loss from the surfaces of the test sections was measured. Based upon the prevailing costs, analyses were performed to determine the economics of using the different dust suppressants. The research indicated that all three dust suppressants studied reduced fugitive dust emission from the unpaved roadways by 50-70%. The treated test sections retained 42-61% more aggregate than the untreated control test section. The cost savings of retaining aggregate on the treated test sections more than offset the costs of the dust suppressants, resulting in an estimated cost savings of 28-42% over the untreated control test section.
TL;DR: Improvements in traffic operations at the electronic toll collection plazas of the Orlando-Orange County Expressway Authority are reported and the measured capacity has tripled, the service time has decreased, and variability in the headway has been reduced significantly in the dedicated E-PASS lane.
Abstract: This paper reports the improvements in traffic operations at the electronic toll collection plazas of the Orlando-Orange County Expressway Authority. Service time, vehicle arrival times, and departure times, as well as vehicle counts were collected “before” and “after” the installation of automatic vehicle identification technology known as E-PASS. The findings indicate that, for the dedicated E-PASS lane, the measured capacity has tripled, the service time has decreased by five seconds per vehicle, the average queuing delay has decreased by one minute per vehicle, the maximum queuing delay has decreased by 2.5–3 minutes per vehicle, and the total queuing delay has decreased by 8.5–9.5 vehicle-hours per morning peak hour for that lane. Also, variability in the headway has been reduced significantly in the dedicated E-PASS lane. Capacity, headway, and service times of the mixed (manual/E-PASS or automatic/E-PASS) lanes did not change significantly. However, arrivals have shifted to the dedicated E-PASS lan...
TL;DR: In this article, a mixed integer linear programming model is introduced for the design of lane uses and signal phases, and performs the optimization simultaneously, and the results indicate significant improvement in minimizing overall delay, stop, and fuel consumption.
Abstract: The development of a codable model for the design of lane-use and signal-phase control at isolated intersections is valuable especially in developing countries where experienced traffic engineers are scarce. Extensive research concerning the design of signal phases and timing have been conducted in the past while very little has been done for the optimal design of the lane use or lane-configuration of intersection approaches. However, poor matching of lane-use design and signal-phase design also produces a poor overall result. It is therefore necessary to integrate the design of lane uses and signal phases, and perform the optimization simultaneously. A mixed integer linear programming model is introduced for this purpose. The resultant designs are verified by comparing their performance indices with that of the existing designs as computed by TRANSYT-7F. The traffic data used are collected from a selected area of Shenzhen, one of the largest special economic zones of the People’s Republic of China. The results indicate significant improvement in minimizing overall delay, stop, and fuel consumption.
TL;DR: In this article, a model developed by the writers is used to study the effects of considering three-dimensional (3D) alignment on design requirements for sight distance, and the authors concluded that 3D-based design standards should be developed and used in highway geometric design.
Abstract: According to current highway design standards, horizontal and vertical alignments are treated separately in two-dimensional (2D) projections. In this paper, a model developed by the writers is used to study the effects of considering three-dimensional (3D) alignment on design requirements for sight distance. First, the paper examines the required minimum radius of a horizontal curve combined with a crest or sag vertical curve in a cut section. Also, the required minimum length of a crest vertical curve combined with a horizontal curve in a fill section is studied. The results show that the 3D design requirements may differ significantly from those in separate 2D projections. Depending on the vertical alignment and on the cut side-slope, 2D design may underestimate or overestimate the required radius. In fill sections, the 2D alignment overestimates the required length of the crest vertical curve when combined with long horizontal curves. In summary, the 2D alignment can compromise both safety and economics of highways. As a result, it is concluded that 3D-based design standards should be developed and used in highway geometric design.
TL;DR: In this paper, the effect of pipe walls, coatings, and surrounding fill on water hammer in pipes is evaluated and it is shown that large volume standpipes can reduce water hammer due to air valve slamming by providing an air cushion.
Abstract: Many water hammer studies concentrate on the main pipeline and pump stopping. Important details can be overlooked. The rigidity of pipe walls, coatings, and surrounding fill on water hammer in pipes is evaluated. It is shown that backfill increases rigidity and celerity marginally, but pipe material is a major factor in water hammer pressures. The effect of air is to reduce wave celerity but increased surging can occur with some pipework configurations, particularly if air can be trapped. Pump startup can then result in severe water hammer. The correct selection of air valve size and standpipe used to minimize water hammer is discussed. The problem of air valves slamming shut during discharge is investigated and can be remedied with a nomograph. It is shown that large volume standpipes can reduce water hammer due to air valve slamming by providing an air cushion. Other problems of air release and sizing and positioning of air valves are discussed in order to reduce the problem of water hammer.
TL;DR: In this article, a new transition curve to be used in the design of the horizontal geometry of routes has been examined, which is an alternative curve to the well-known classical transition curve, formed by spiral curve-circular are spiral curve.
Abstract: In this paper, a new transition curve to be used in the design of the horizontal geometry of routes has been examined. This curve joins two straight lines with a single element. It is an alternative curve to the well-known classical transition curve, which is formed by spiral curve-circular are spiral curve. In order to compare the suggested transition curve with the classical transition curve in terms of the vehicle-road dynamics, the curvature and superelevation functions of both curves are derived, and funcions of the lateral change of acceleration of both curves are obtained and illustrated graphically for the seven selected motion models. The comparisons that take into account the discontinuities in the form of jumps in the graphics of the lateral change of acceleration have shown that the new transition curve is superior to the classical transition curve for all seven motion models. Language: en
TL;DR: In a theoretical sense, this paper shows that dynamic ride-sharing is a viable concept, and for a congested freeway corridor, the number of trips generated per unit time and space should be sufficient to yield a reasonably large population of potential ride-matches for a DR system.
Abstract: Dynamic Ride-sharing (DR) is envisioned as an automated process by which individuals find ride-matches on a trip by trip basis. This paper examines the DR concept on both a theoretical basis and on the basis of actual implementation in Los Angeles. Specifically, the paper investigates the likelihood that the user of a DR system would be successful in finding a ride-match. In a theoretical sense, this paper shows that dynamic ride-sharing is a viable concept. For a congested freeway corridor, the number of trips generated per unit time and space should be sufficient to yield a reasonably large population of potential ride-matches for a DR system. Unfortunately, as demonstrated in the experiment, theory and practice are not the same. Even when individuals share common trip patterns, consummating a ride-match is no easy task for logistical reasons. At best, one might expect a one in five chance of someone offering a ride when trip patterns are similar. This probability would decline for casual trips, and when contacting individuals who have not expressed a prior willingness to carpool.
TL;DR: In this paper, a deterministic simulation model has been developed to precisely estimate train motions and performance using basic equations for kinematics, resistance, power, and braking for a 1% dip (i.e., a vertical dip equal to 1% of station spacing).
Abstract: Dipped track profiles between rail transit stations can significantly reduce propulsive energy, braking energy, and travel times. This work quantifies their potential benefits for circumstances reflected in various values for dips, speed and acceleration limits, station spacings, and available power. A deterministic simulation model has been developed to precisely estimate train motions and performance using basic equations for kinematics, resistance, power, and braking. For a 1% dip (i.e. a vertical dip equal to 1% of station spacing) in which gradients never exceed 4%, our results show savings (compared with level tracks) exceeding 9% for propulsive energy, 15% for braking energy, and 5% for travel time between stations.
TL;DR: In this paper, a viscoelastic solution of the diametral compression of short cylinders has been presented for analyzing the haversine load history, and expressions for the real and imaginary parts of the complex compliance, as functions of phase angles and amplitudes measured in tests, are derived for their evaluation.
Abstract: A viscoelastic solution of the diametral compression of short cylinders has recently been presented by this paper's authors. The solution is based on Hondros's elastic solution and applies to any load history. In this paper, the viscoelastic solution is used for analyzing the haversine load history. Expressions are derived for the real and imaginary parts of the complex compliance, as functions of phase angles and amplitudes measured in tests, and algorithms are presented for their evaluation. The theoretical solution is illustrated with a series of tests on two asphalt concrete mixtures, subjected at room temperature to haversine loading over a wide range of frequencies. It is shown that power-law creep compliance satisfactorily describes the deviatoric viscoelastic behavior of the tested materials. The volumetric behavior, on the other hand, is nearly frequency-independent and can be approximated by a purely elastic law. The results of this paper demonstrate that incorporating viscoelasticity in the interpretation of the diametral compression test is viable and provides valuable information on asphalt concrete viscosity-related properties.
TL;DR: In this paper, the authors provide an overview of the results of recent research related to pavement and vehicle dynamics and their interaction and evaluate their potential use in the design and management of pavements.
Abstract: The interaction between vehicle and pavement is complex since pavement roughness excites the dynamic forces generated by vehicles, while these dynamic forces simultaneously increase the pavement roughness. The objective of this paper is to provide an overview of the results of recent research related to pavement and vehicle dynamics and their interaction and to evaluate their potential use in the design and management of pavements. Pavement dynamic models are capable of determining stresses, strains, and deflections in various directions when harmonic, pulse, or transient loads are applied. Vehicle dynamic models simulate the effect of pavement roughness on the inertia of various vehicle components. These models can predict the dynamic forces produced by different axles and wheels of traveling vehicles at different locations along the pavement. Pavement response computed using dynamic models matches field measurements closer than those computed using static models. The concept of vehicle-pavement interaction can be applied to weigh-in-motion, pavement design and performance, and vehicle regulations.
TL;DR: In this paper, the static and dynamic deflection responses from the ABAQUS model of an uncracked pavement are validated using field data from two in-service pavements, and regression equations that predict surface deflection bowls in terms of layer moduli and thicknesses are developed.
Abstract: The static elastic layer model is customarily used for analyzing deflection measurements and back-calculating pavement layer moduli. Estimation of in-situ layer moduli by means of a mechanistically based iterative technique is known as back-calculation. Despite the fact that the falling weight deflectometer (FWD) load induces a dynamic load, dynamic/impact analysis routines are seldom, because of the mathematical complexity. Dynamic deflection prediction models are developed in this study, which can be used in back-calculation routines. The first step in accomplishing this is to select an appropriate analysis model for which ABAQUS, a general purpose finite-element program, is used. Static and dynamic deflection responses from the ABAQUS model of an uncracked pavement are validated. Following this first step, cracks and joints along with other features of the pavement are modeled in addition to nonlinear behavior of pavement materials. Deflection responses of cracked pavement under a series of increasing loads, assuming linear and nonlinear behavior of base, subbase, and subgrade materials, are computed and compared. After finalizing the model, a synthetic deflection database, specifically with FWD load, is developed relying on a fractional factorial design layout in which thicknesses, layer moduli, and cracks are allowed to vary over a range. Making use of this database, regression equations that predict surface deflection bowls in terms of layer moduli and thicknesses are developed. Deflection equations are validated using field data from two in-service pavements.
TL;DR: Application and extensions of a dynamic network equilibrium model to the Advanced Driver and Vehicle Advisory Navigation Concept (ADVANCE) Network are described and computational results are presented and analyzed.
Abstract: Application and extensions of a dynamic network equilibrium model to the Advanced Driver and Vehicle Advisory Navigation Concept (ADVANCE) Network are described in this paper. ADVANCE is a dynamic route guidance field test designed for 800 km(superscript 2) in the northwestern suburbs of Chicago. The dynamic route choice model employed in this paper is solved efficiently by a modified version of Janson's DYMOD algorithm. Realistic traffic engineering-based link delay functions, instead of the simplistic Bureau of Public Roads (BPR) function, are used to estimate link travel times and intersection delays for most types of links and intersections. Further, an expanded intersection representation is utilized, resulting in a network of nearly 23,000 links and 10,000 nodes. Time-dependent link flows, travel times, speeds and queue spillbacks are generated for the ADVANCE Network. The model was solved on a CONVEX-C3880. Convergence and computational results are presented and analyzed.
TL;DR: In this paper, a study was conducted to determine the drainability characteristics of several types of unbound granular materials that are used in pavement bases, and the average hydraulic conductivities for the open and dense-graded materials were 3.6 × 10/u-¹ and 3.0 × 10\u-\u4 cm/s (1,021 and 0.85 ft/d), respectively.
Abstract: A study was undertaken to determine the drainability characteristics of several types of unbound granular materials that are used in pavement bases. From the literature, testing concerns were identified and analyzed. Hydraulic conductivity and effective porosity were determined for aggregates from two sources of crushed stone and two sources of gravel. For each material two open gradations were tested in a rigid wall permeameter. One dense gradation of each material, at two levels of compaction, was tested in a flexible wall permeameter as well. Efforts were made to reduce possible flow along the sides of the rigid wall permeameter and to eliminate problems with air bubbles. The average hydraulic conductivities for the open and dense-graded materials were 3.6 × 10\u-¹ and 3.0 × 10\u-\u4 cm/s (1,021 and 0.85 ft/d), respectively. The effective porosities for the open and dense-graded materials were 68 and 27% of the nominal porosities, respectively. Four regression equations representing a wide range of hydraulic conductivity were developed to estimate hydraulic conductivity based on the results of this study and others reported in the literature.
TL;DR: A three-dimensional evaluation taxonomy is formulated: road pricing strategies, impacted groups, and impacts, which serves as a framework to study the literature and highlight state-of-the-art evaluation approaches and available modeling tools as well as to identify those lacking.
Abstract: Recent advances in road pricing technology and the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991, which authorized $25,000,000 to fund congestion pricing demonstration projects, have created a resurgence of interest in the topic of road pricing, particularly in the form known as congestion pricing. However, review of the considerable literature on this topic has shown very little discussion on the need to evaluate the congestion pricing demonstration projects. Responding to this need, the paper presents an evaluation framework that may guide the evaluation efforts for these demonstration projects. We formulated a three-dimensional evaluation taxonomy: road pricing strategies, impacted groups, and impacts. We then used the taxonomy as a framework to study the literature so as to highlight state-of-the-art evaluation approaches and available modeling tools as well as to identify those lacking. Despite the large body of work published in this area, it appears that a major effort is needed to streamline and, in some cases, calibrate existing models so they may be used for evaluation purposes.
TL;DR: In this paper, the authors investigated the performance of safety evaluation methods and estimate the safety effectiveness of street bumps, closing of median openings, and divisional islands in an urban environment.
Abstract: The main objective of this study was to investigate the performance of safety evaluation methods and estimate the safety effectiveness of street bumps, closing of median openings, and divisional islands in an urban environment. Traffic accident data were obtained from the municipality of Irbid, Jordan, and its police records. In the analysis the performances of simple before-and-after and empirical Bayesian methods were compared with results obtained by comparison group methods. The results indicate that the simple before-and-after method overestimated the effectiveness of safety improvements and led to erroneous conclusions at specific locations, as well as at the aggregate level. The comparison group method and the empirical Bayesian method provided results comparable to each other. Based on the results of the comparison group and the Bayesian methods, the study indicates that street bumps and closing of median openings at intersections are effective in reducing total accidents. In contrast, implementation of divisional islands did not provide a significant reduction.
TL;DR: In this article, the effects of different trench backfill materials, pipe burial depths, and pipe materials on the amount of traffic load transferred to buried pipe was investigated. And the results showed that the use of trench backfills such as controlled low strength material (CLSM) instead of traditional materials such as sand and clay, results in significantly reduced stresses in polyvinyl chloride (PVC) pipe under traffic loading.
Abstract: Nonlinear finite-element analyses have been carried out to assess the effects of different trench backfill materials, pipe burial depths, and pipe materials on the amount of traffic load transferred to buried pipe The analyses show that the use of trench backfills such as controlled low strength material (CLSM) instead of traditional materials such as sand and clay, results in significantly reduced stresses in polyvinyl chloride (PVC) pipe under traffic loading This finding is in agreement with recent truck load tests carried out in the City of Edmonton, where strains were monitored on buried PVC water mains The protection of buried pipes under or in CLSM backfill from traffic loading becomes more significant with the decrease in pipe burial depth and stiffness The reasons behind the difference in load transfer between the traditional backfills and CLSM are the high elastic modulus and strength of CLSM, as well as uniform load transfer along the longitudinal axis of the pipe
TL;DR: In this paper, the data collected under the R-6 research project of the Ministry of Surface Transport, India, has been used to develop prediction models and growth curves for rebound deflection, rut depth, and crack area of pavements considering two types of surfacing: BM (bituminous macadam) + PC (premix carpet) and BM + AC (asphaltic concrete), commonly practiced in India.
Abstract: Due to the combined influence of traffic loading and environment, the structural condition of pavement deteriorates with time. Studies on structural damage, which usually results in functional deterioration, is important for the highway engineer to plan the maintenance/strengthening strategies to extend the life of pavements. In the present investigation, the data collected under the R-6 research project of the Ministry of Surface Transport, India, has been used to develop prediction models and growth curves for rebound deflection, rut depth, and crack area of pavements considering two types of surfacing: BM (bituminous macadam) + PC (premix carpet) and BM + AC (asphaltic concrete), commonly practiced in India. The performance of the pavements were studied and comparative analysis was made in terms of growth in deflection, rut depth, and crack area. An attempt has been made to develop failure envelopes based on selected critical rut depth criteria. The results are useful to decide the timing for maintenance/rehabilitation programs.
TL;DR: In this article, the authors introduce a systematic approach to determine the need for and location of truck escape ramps (TERs), which utilizes variables concerning the design vehicle, the road, and the driver.
Abstract: The main objective of this paper is to introduce a systematic approach to determine the need for and location of truck escape ramps (TERs). The approach utilizes variables concerning the design vehicle, the road, and the driver. These variables are included in either a stochastic or deterministic form. Vehicle variables include vehicle type, gross vehicle weight, and brake type. Road variables include the profile (length and steepness of grade), horizontal curvature (cornering speed), and the availability of a brake-check area at the top of the grade. Driver variables include information about the driver's actions at the brake-check area, brake checking, and gear selection. A number of supplementary variables are also included, such as accident history and the presence of objects in the path of a runaway vehicle. The approach also utilizes a number of existing vehicle-road performance models to generate relevant data concerning the descent speed, cornering stability, and brake temperature. The application of the methodology is illustrated with examples from highways in mountainous terrain of Jordan and western Canada. The examples selected are diverse and were chosen to illustrate the generalized nature of the methodology.
TL;DR: In this article, the authors determine the service lives of three different types of joint sealants (polyvinylchloride (PVC)-coal tar, rubberized asphalt, and silicone) and recommend maintenance strategies to improve the performance of concrete pavements in Utah.
Abstract: The objective of this research project is to determine the service lives of three different types of joint sealants—polyvinylchloride (PVC)-coal tar, rubberized asphalt, and silicone—and to recommend maintenance strategies to improve the performance of concrete pavements in Utah. The silicone material has been performing well for over 10 years. The PVC-coal tar material had failed in the test sections that are an average of 15 years old, and the rubberized asphalt material has aged beyond its expected service life in the test sections over 20 years old. Survival curves of the three sealants were developed with respect to their ages, and their performance correlated well with their ages. The conical spalling at the bottom of the joints increased after 10 years of service. Based on the limited field data, it is recommended that Utah Department of Transportation (UDOT) should consider the use of a narrower joint width of 6 mm instead of the current 9-mm design, use silicone or rubberized asphalt material, and implement a maintenance plan with a 10-year cycle for recutting and resealing of the joints to 9 x 9 mm.