Showing papers in "Journal of Transportation Engineering-asce in 1998"
TL;DR: The use of genetic algorithms (GAs), a search and optimization method based on natural genetics and selection, in solving the route network design problem is reported.
Abstract: Urban bus route network design involves determining a route configuration with a set of transit routes and associated frequencies that achieves the desired objective. This can be formulated as an optimization problem of minimizing the overall cost (both the user's and the operator's) incurred. In this paper, the use of genetic algorithms (GAs), a search and optimization method based on natural genetics and selection, in solving the route network design problem is reported. The design is done in two phases. First, a set of candidate routes competing for the optimum solution is generated. Second, the optimum set is selected using a GA. The GA is solved by adopting the usual fixed string length coding scheme along with a new variable string length coding proposed in this study. The former assumes a solution route set size, and tries to find that many best routes from the candidate route set, using a GA. The route set size is varied iteratively to find the optimum solution. In the newly proposed variable stri...
344 citations
TL;DR: In this article, a continuum-based finite-layer approach is proposed to evaluate pavement strain response under actual traffic loading, incorporating important pavement response parameters such as the dynamic tire-pavement load variations and corresponding complex contact stress distributions (normal and shear), vehicle speed, and viscoelastic material characterization.
Abstract: This paper presents the formulation and the application of a continuum-based finite-layer approach to evaluate pavement strain response under actual traffic loading. The model incorporates important pavement response parameters such as the dynamic tire-pavement load variations and corresponding complex contact stress distributions (normal and shear), vehicle speed, and viscoelastic material characterization. Results of a parametric study in which two typical thin and thick pavement sections were subjected to traffic loading moving at different speeds are included. As an important application of the proposed method, pavement strain responses generated by wide-base and dual tires have been presented. This study reveals that contradictory to the past studies, the impact of tire-pavement contact shear stress on tensile strain at the bottom of asphalt concrete is insignificant.
164 citations
TL;DR: In this article, the authors investigated the behavior of pedestrians in choosing between escalators and stairways in Hong Kong Mass Transit Railway (MTR) stations during peak hours and found that pedestrians are more sensitive to the relative delays when using the vertical pedestrian facilities in the descending direction than in the ascending direction.
Abstract: Passenger demands on underground stations are always excessive and can cause severe congestion. The study of pedestrian behavior is particularly important in planning and design of the underground stations during peak hours. This paper reports an investigation on the behavior of pedestrians in choosing between escalators and stairways in Hong Kong Mass Transit Railway (MTR) stations during peak hours. Time-lapse photography surveys were conducted in six selected MTR stations to collect the relevant data. The travel time functions of the vertical pedestrian facilities have been calibrated and are used for developing the pedestrian route choice model. Service levels have been defined for the vertical pedestrian facilities based upon the service levels defined by previous researchers. It was found that the stairway capacities in the ascending and descending directions in the Hong Kong Mass Transit Railway stations are higher than in London Underground stations. It was also found that the pedestrians are more sensitive to the relative delays when using the vertical pedestrian facilities in the descending direction than in the ascending direction.
144 citations
TL;DR: The results show that the genetic algorithm is able to search for two sets of parameter values that enable FRESIM to produce 30-s loop-detector volume and speed closely matching the field data under two different traffic conditions.
Abstract: FRESIM is a microscopic time-stepping simulation model for freeway corridor traffic operations. To enable FRESIM to realistically simulate expressway traffic flow in Singapore, parameters that govern the movement of vehicles needed to be recalibrated for local traffic conditions. This paper presents the application of a genetic algorithm as an optimization method for finding a suitable combination of FRESIM parameter values. The calibration is based on field data collected on weekdays over a 5.8 km segment of the Ayer Rajar Expressway. Independent calibrations have been made for evening peak and midday off-peak traffic. The results show that the genetic algorithm is able to search for two sets of parameter values that enable FRESIM to produce 30-s loop-detector volume and speed (averaged across all lanes) closely matching the field data under two different traffic conditions. The two sets of parameter values are found to produce a consistently good match for data collected in different days.
112 citations
TL;DR: The results of a laboratory study on the influence of standard Proctor and West African standard compactive efforts as well as compaction delays up to 3 h on the compaction and strength characteristics of lateritic soil treated with a maximum of 8% lime (by dry weight of soil) is presented in this paper.
Abstract: The results of a laboratory study on the influence of standard Proctor and West African standard compactive efforts as well as compaction delays up to 3 h on the compaction and strength characteristics of lateritic soil treated with a maximum of 8% lime (by dry weight of soil) is presented. The results obtained show that the compaction and strength properties of the lime-treated soil decreased with increases in compaction delays. The decreases that were generally greater at higher lime contents were more prominent in specimens compacted at the energy of the West African standard. The determination of properties of lime-treated soil at no compaction delay defines optimum properties of the soil-lime mixtures, while compaction and strength properties determined following compaction delays define the minimum that can be achieved in the field for the specified elapsed times between mixing and compaction.
95 citations
TL;DR: This paper examines how new objectives and environmental considerations can be modeled within the traditional, macroscopic traffic assignment methodology and develops a new methodology for modeling the assignment of vehicles in realistic networks based on equitable, rather than user-equilibrium or system-optimal, principles.
Abstract: In the past 10 years increased importance has been placed on public participation and environmental concerns in transportation system decision-making. While there are numerous societal objectives to consider when planning and operating a transportation system, it is not clear whether the optimal strategy with respect to one objective is also the optimal strategy with respect to the other objectives. This paper examines how new objectives and environmental considerations can be modeled within the traditional, macroscopic traffic assignment methodology. In addition, a new methodology for modeling the assignment of vehicles in realistic networks is developed based on equitable, rather than user-equilibrium or system-optimal, principles. The basic premise is that with the advent of intelligent transportation systems (ITS) the operation of the transportation system based on the objectives of the general public, rather than the traveling public and system operators, is feasible. A methodology for modeling these situations is required. All of the approaches discussed here were tested on a calibrated network from Edmonton, Alberta, Canada.
93 citations
TL;DR: In this article, the effect of lime content, curing period, and compactive effort on the permeability of lateritic soil-lime mixtures prepared at various maximum dry densities and corresponding optimum moisture contents was evaluated.
Abstract: Laboratory investigations were carried out on a residual lateritic soil treated with quicklime (up to 8% by weight of dry soil) in order to evaluate the effect of lime content, curing period, and compactive effort on the permeability of lateritic soil-lime mixtures prepared at various maximum dry densities and corresponding optimum moisture contents. The permeability of uncured specimens (standard Proctor) increased to a maximum at 4% lime content and decreased with increasing lime content. Specimens compacted at the energy of the West African Standard had coefficients of permeability that decreased with increasing lime content. For the cured condition, the permeability of all the lime-treated specimens compacted at the two energy levels increased with curing age up to 14 days and decreased with curing age beyond 14 days.
86 citations
TL;DR: In this article, a series of statistical characteristics of wheel loads in frequency domain and time domain are presented, and the motion properties of dynamic loads were described by means of Dirac-delta and Heaviside functions, and its randomness property was studied using a quarter-truck vehicle model.
Abstract: Dynamic loads caused by vehicle-pavement interaction are either moving loads or random loads. The motion property of dynamic loads was described by means of Dirac-delta and Heaviside functions, and its randomness property was studied using a quarter-truck vehicle model. A series of statistical characteristics of wheel loads in frequency domain and time domain are presented in this paper. It was found that dynamic loads are a constant mean Gaussian stationary ergodic process whose power spectral density is in proportion to the power spectral density of pavement roughness, whereas the ratio coefficient relates to dynamic properties of vehicle and velocities of travel. Numerical simulation based on the specifications of the International Organization for Standardization (ISO) indicated that only at low speed could dynamic loads be treated as quasi-narrow bandwidth random processes, which covers the frequency range of 1.0-4.0 Hz. At high speed, main frequency distributions of dynamic loads occur in 1.0-4.0 and 10.0-15.0 Hz. Further analysis also showed that according to the ISO specifications, the root mean square of dynamic loads is proportional to the square root of C sub(SP), an important index related to pavement levels.
74 citations
TL;DR: In this article, the authors demonstrate the usefulness of the finite-element method in the analysis of three-layer pavement systems subjected to different types of loading, such as axle load with different tire pressures, axle loads with different configurations, and axle loads traveling at different speeds.
Abstract: This study illustrates the usefulness of the finite-element method in the analysis of three-layer pavement systems subjected to different types of loading. The method is capable of simulating the observed responses of pavements subjected to axle loads with different tire pressures, axle loads with different configurations, and axle loads traveling at different speeds. A variety of material constitutive models such as linear elastic, nonlinear elastic, and viscoelastic are employed in the analyses to describe the behavior of the pavement materials. Finite-element modeling of pavements, if validated, can be extremely useful, because it can be used directly to estimate primary response parameters without resorting to potentially costly field experiments. If accurate correlations between the calculated and the measured primary response parameters can be obtained, then the analytical model can be used to calculate primary response load equivalency factors, utilizing deflection-based or strain-based equivalency factor methods.
72 citations
TL;DR: This paper presents an analysis of freeway traffic flows under congestion based on the principle of traffic dynamics, using the example of recurring congestion, to imply that the guidelines of the 1994 Highway Capacity Manual may result in the underestimation of congestion-related statistics.
Abstract: This paper presents an analysis of freeway traffic flows under congestion based on the principle of traffic dynamics, using the example of recurring congestion. Queuing and discharging mechanisms are analyzed using the fundamental concept of conservation of vehicles. These analysis results are applied for reviewing the two conventional macroscopic analysis tools, deterministic queuing analysis and shock-wave analysis. Comparative study results have demonstrated that (1) the two methods are fundamentally different from the traffic modeling point of view; (2) deterministic queuing analysis always underestimates the overall magnitude of delays compared to shock-wave analysis; and (3) the area between the demand and the capacity curves in a queuing diagram is analytically equivalent to total vehicle-hours of travel in congestion as opposed to the widely accepted total vehicle-hours of delay. The study results imply that the guidelines of the 1994 Highway Capacity Manual may result in the underestimation of congestion-related statistics. For the purposes of illustration and verification, a numerical example problem is provided.
61 citations
TL;DR: The proposed maximal O-D selection method is proved to provide results with a comparable level of reliability, and a sensitivity test is conducted with different objective functions to verify this proposed method.
Abstract: Origin-destination (O-D) trip matrix estimation from traffic count surveys is regarded as the most economical and effective methodology in road network analysis for transport planning and traffic management. Despite the numerous mathematical estimation techniques previously developed, the fundamental procedure of selecting count locations itself is a prime determinant in the quality of the ultimate estimation and deserves more in-depth exploration. In this paper, some existing methods being adopted in practice are reviewed. Two basic rules are established based on previous works and are formulated in a linear programming model to determine the best survey locations for O-D estimation. However, technical problems will be incurred when applied to a large network with huge number of variables involved. The proposed maximal O-D selection method is proved to provide results with a comparable level of reliability, and a sensitivity test is conducted with different objective functions to verify this proposed str...
TL;DR: In this paper, a plate consisting of one or more layers, resting on a general elastic foundation, is subjected to a nonlinear through-the-thickness temperature distribution, together with arbitrary wheel loads.
Abstract: This study considers a plate consisting of one or more layers, resting on a general elastic foundation, and subjected to a nonlinear through-the-thickness temperature distribution, together with arbitrary wheel loads. The resultant bending stress distribution in the plate is presented as the sum of the bending stresses due to the applied loading and to an equivalent linear temperature gradient, plus the pure thermal stresses due to the nonlinear part of temperature distribution. The resulting algorithm has been implemented into finite-element code ILSL2, capable of accommodating one- or two-layered slabs with a temperature distribution through the individual layers described by a linear function, a quadratic function, or explicitly provided by the user at a number of individual depths. Several examples are used to illustrate application of the method.
TL;DR: A simulation model for estimating the delay on an approach to a signal-controlled intersection with a bus stop upstream is developed and a new delay formula was established and calibrated for use in the design of a signal -controlled intersection.
Abstract: Because of the tight constraints on many streets in urban areas, it is not uncommon to situate a bus stop upstream of a signal-controlled intersection without the provision of a proper bus bay or setback. For a single-lane approach, where the overtaking of a stopped bus at the bus stop is prohibited, the setup of such a bus stop would significantly affect the delay incurred by road users. It is believed that the delay in such situations depends on a number of factors, such as the distance between bus stop and stop line, traffic and bus flows, dwell time of buses and signal settings. In this paper, a simulation model for estimating the delay on an approach to a signal-controlled intersection with a bus stop upstream is developed. To test the reliability of the model, field surveys were conducted to validate the simulation model. A good agreement between the observed and simulation results was obtained. When the simulation model was used, a new delay formula was established and calibrated for use in the design of a signal-controlled intersection.
TL;DR: In this article, a simple and practical safety margin, based on an established driver behavior model, is used to investigate two sources of inconsistency: (1) the choice of design speed; and (2) the selection of superelevation and side friction when the curve radius exceeds the minimum.
Abstract: Growing awareness exists of the important role of consistency in highway alignment design in minimizing the frequency and extent of violations of driver expectancy, to improve highway safety. A simple and practical safety margin, based on an established driver behavior model, is used to investigate two sources of inconsistency: (1) The choice of design speed; and (2) the choice of superelevation and side friction when the curve radius exceeds the minimum. This paper describes a method for choosing the design speed for a horizontal curve, taking into account the extent of the curve. The paper also describes alternative methods for choosing the superelevation and side friction. Using a practical numerical example, the design speed selection and superelevation and side friction selection methods are evaluated with respect to consistency of the safety margin. It is concluded that use of the design speed selection method, and having the superelevation and friction varying linearly with the degree of curvature,...
TL;DR: In this article, a frequency-domain back-calculation program, BKGREEN, is introduced to determine the elastic modulus for each pavement layer. But the program is not suitable for the case where the pavement is modeled as a layered elastic s...
Abstract: This paper introduces a frequency-domain back-calculation program, BKGREEN, that can be used to determine the elastic modulus for each pavement layer. The pavement is modeled as a layered elastic s...
Abstract: Traffic volume and travel time data collected at a number of arterial roads in Singapore were used to analyze the speed-flow relationships for radial and ring arterial roads. A new travel time–density model was formulated by incorporating “minimum delay per intersection” and “frequency of intersections per kilometer” as model parameters. The appropriate values of these model parameters also were established. The adjusted R2 value of this model was higher than those for the journey speed–density and running speed–density relationships. The free-flow speed and maximum flow values of the travel time–density model also fitted favorably well with field data compared with those of the journey-speed models. The radial road capacity estimates range from 835 passenger cars per hour per lane (pc/h/l) for segments with uncoordinated (unlinked) traffic signals to 905 pc/h/l for segments with proper signal (linked) coordination. Not much difference in estimated capacities is observed between linked and unlinked segmen...
TL;DR: In this paper, a closed-form analytical solution is presented for a three-layer pavement system, subjected to a periodic variation of either ambient air temperature or pavement surface temperature, coupled with a plate theory with Winkler foundation to calculate curling stresses and bending moments.
Abstract: Temperature is an important factor influencing the functioning of concrete pavements. In the past, analysis of temperature distribution in pavement has been done using numerical techniques such as finite difference or finite element method; both require significant computational efforts. In this paper, a closed-form analytical solution is presented for a three-layer pavement system, subjected to a periodic variation of either ambient air temperature or pavement surface temperature. The thermal analysis is coupled with a plate theory with Winkler foundation to allow for calculation of curling stresses and bending moments. The methods for characterizing periodic temperature variations are also described. The main findings from the numerical studies show that the temperature distribution with depth can be highly nonlinear, particularly when daily temperature variation is considered. Thus, the frequency of temperature variation, rather than the amplitude, has the most significant effect on the calculated temperature distribution with depth in the concrete pavement layer. A frequency of 2 pi rad/d or higher can be expected to cause nonlinear temperature distribution and require that calculation of curling stresses be based on a nonlinear distribution model.
TL;DR: In this article, the authors examined the nature of uncertainty present in transport planning and explored appropriate mathematical treatment, and applied the appropriate mathematical technique to model these types of uncertainty, along with the basic properties of fuzzy set theory and evidence theory.
Abstract: This paper examines the nature of uncertainty present in transport planning and explores appropriate mathematical treatment. Two types of uncertainty are dealt with: vagueness and ambiguity. The former refers to the uncertainty caused by the lack of definition of words, and the latter refers to the uncertainty caused by the lack of information about the subject matter. The mathematical framework that can deal with vagueness is fuzzy set theory, and that for ambiguity is evidence theory. Differences in the nature of problems that these two types of uncertainty present are examined. How to apply the appropriate mathematical technique to model these types of uncertainty is discussed, along with the basic properties of fuzzy set theory and evidence theory. Domains of transport problems that are conducive to these theories are explained, and the issues that need to be examined when using these theories are discussed.
TL;DR: The present study describes the methodology of simulating the traffic flow and thereby estimating the number of conflicts in varying traffic flow conditions, and the model was validated externally, using field observed data, and was found to predict thenumber of conflicts well.
Abstract: The behavior of traffic in the heterogeneous environment of an urban uncontrolled intersection is complex and difficult to model. The present study describes the methodology of simulating the traffic flow and thereby estimating the number of conflicts in varying traffic flow conditions. The arrival pattern of vehicles was represented by a multivariate distribution to generate input to the simulation model. The model was validated externally, using field observed data, and was found to predict the number of conflicts well. As an illustration of usefulness of the model, variation of conflict rate (the probability of a vehicle's getting involved in conflict) due to variation in traffic volume and the proportion of right-turning traffic has been quantified. Under the prevailing traffic composition and turning movements, the conflict rate is estimated to lie in the range of 0.66-0.70, 0.79-0.84, and 0.80-0.87 for intersection volumes of 2,000, 2,500, and 3,000 vehicles per hour, respectively. Issues related to the applicability of the proposed model are briefly discussed.
TL;DR: In this article, a new elastoplastic model is presented for predicting the stress-strain response of asphalt concrete under cyclic loading, which utilizes multi-yield surfaces and isotropic hardening.
Abstract: A new elastoplastic model is presented for predicting the stress-strain response of asphalt concrete under cyclic loading. The model utilizes multiyield surfaces and isotropic hardening. Rowe's stress dilatancy theory is used to obtain the relationship between the permanent volumetric and vertical strains as well as the hardening law for the changes in the sizes of the plastic moduli caused by cyclic loading. These relationships considerably simplify the task of predicting the plastic deformation under cyclic loading of both triaxial compression and extension tests. A complete description of the plastic deformation of asphalt concrete under cyclic loading is treated, including the elastic, viscoelastic, and plastic components as well as the relationship between rutting and cracking. A computer program, called Rutting in Asphalt Concrete (RUT), determines the plastic deformation under cyclic loading. Good agreement exists between the model predictions and experimental data that include data published by other researchers.
TL;DR: A mathematical model is presented that enables the determination of the safe PSD and calculates the desired trajectory for overtaking on two-lane highways and explains why the standards given in the AASHTO study of 1994 could be thought to be conservative.
Abstract: The maximum permitted length of trucks in North America and other parts of the world has increased significantly over the past 20 years This has led to concern regarding the interaction of trucks with other elements in the traffic stream There are many highway infrastructure design criteria that need to be reassessed in light of recent evidence on the behavior and properties of trucks One of them is the passing sight distance (PSD), which is crucial for a safe overtaking maneuver In addition, to overcome the increased congestion of modern roads, the development of the Intelligent Transportation System also requires an on-line overtaking model, which is able to provide the desired trajectory for the control This paper presents a mathematical model that enables the determination of the safe PSD and calculates the desired trajectory for overtaking on two-lane highways In addition to vehicle length, 10 other parameters that have an an effect on the PSD are also included in this model Specifically, the effects of various input parameters have been examined Simulation results from this model are compared with those suggested by the American Association of State Highway and Transportation Officials (AASHTO) to test the validity of the model Also, we explain why the standards given in the AASHTO study of 1994 could be thought to be conservative
TL;DR: In this paper, the Task Committee on Freight Pipelines, Pipeline Division, ASCE, issued a report on freight pipelines of various types (including slurry pipeline, pneumatic pipeline, and capsule pipeline).
Abstract: This report is issued by the Task Committee on Freight Pipelines, Pipeline Division, ASCE. Freight pipelines of various types (including slurry pipeline, pneumatic pipeline, and capsule pipeline) h...
TL;DR: The serviceability rating of roads has been an interesting and important subject ever since it was introduced to measure the road performance as mentioned in this paper, and the present paper analytically addresses this problem.
Abstract: The serviceability rating of roads has been an interesting and important subject ever since it was introduced to measure the road performance. The present paper analytically addresses this problemn...
TL;DR: Video detection systems that currently seem to be the most attractive alternative to the traditional intrusive methods are described, and a few popular video systems are presented in some detail.
Abstract: There is a need for advanced traffic management systems (ATMS) on a local and network level to effectively utilize today`s transportation system. An automated operating system, with round the clock incident detection, would help to initiate the required action on time in case of an accident and would minimize the effect of the incident. One of the key elements of ATMS is the vehicle detection unit. The most commonly used inductive loop detectors have a relatively short life span and frequently malfunction. Any maintenance of loop detectors requires road closures. Also, safety of the crew is an issue. An overview of currently available technologies for traffic control and monitoring is presented, with special emphasis on systems that can be installed and maintained without significantly interfering with the traffic. The paper presents the available technologies, provides comparative information about them, and discusses the technical and conceptual problems typically arising during the deployment. The paper describes video detection systems that currently seem to be the most attractive alternative to the traditional intrusive methods. The new perspectives for traffic monitoring and management not available so far are drawn. The typical architecture of these systems is described, and a few popular video systems aremore » presented in some detail. The most critical deployment issues, such as the choice of the equipment, are described, the location of the sensors is discussed, and data transmission problems are considered.« less
ILOG1
TL;DR: A network-based method is proposed to transform all the sequence and constraint relations of aircraft at gates into a network and the superiority of the proposed method over the event-driven method is revealed through comprehensive comparisons of their overall simulation performance.
Abstract: Simulation is becoming an essential tool for planning, design, and management of airport facilities. A simulation of aircraft at gates at an airport can be applied for various periodically performed applications, relating to the dynamic behavior of aircraft at gates in airport terminals for analyses, evaluations, and decision supports. Conventionally, such simulations are implemented using an event-driven method. For a more efficient simulation, this paper proposes a network-based method. The basic idea is to transform all the sequence and constraint relations of aircraft at gates into a network. The simulation is done by calculating the longest path to all the nodes in the network. The effect of the algorithm of the proposed method has been examined by experiments, and the superiority of the proposed method over the event-driven method is revealed through comprehensive comparisons of their overall simulation performance.
TL;DR: In this paper, an analytical model is developed to optimize bus service with their demand characteristics, while route spacing and headway are included with or without vehicle capacity constraints, and the optimal levels of these variables are obtained analytically for the objective functions of profit maximization.
Abstract: Analytical models are developed to optimize bus service with their demand characteristics. The optimizing bus services design options are analyzed in this paper, while route spacing and headway are included with or without vehicle capacity constraints. Optimal levels of these variables are obtained analytically for the objective functions of profit maximization. The analysis uses an equilibrium framework with transient ridership sensitive to the level of service provided by the bus system. The major results consist of closed-form solutions for the optimal area operating policies that are dependent upon local conditions (vehicle capacity constraints) and coefficients of the demand.
TL;DR: In this article, the authors explore the use of small-scale models of accelerated pavement testing devices to evaluate the performance of pavements in conjunction with full-scale tests and conclude that even when full similitude is not satisfied, it is possible to obtain valid results that can be extrapolated to predict prototype performance if one were interested primarily in the behavior of the asphalt layer.
Abstract: This paper presents the results of a study conducted to explore the use of small-scale models of accelerated pavement testing devices to evaluate the performance of pavements in conjunction with full-scale tests. The motivation for the study was the availability of a model mobile load simulator (MMLS), which had been built originally to illustrate the operation of the full-scale mobile load simulator under design at the time. The scaling requirements will be different depending on whether dynamic (inertia), viscous, or gravity effects are important. One must thus decide which one of these effects controls the behavior to try to reproduce it exactly. In the preliminary tests conducted with the MMLS, emphasis had been placed in reproducing accurately the viscoelastic behavior of the asphalt layer. The possibility of obtaining valid results, even if similitude is not maintained in relation to inertia forces, is explored in this paper. The effects of load frequency or velocity and the effects of layer thicknesses are studied. The total thickness of the model pavement, which must be finite, and its effects on displacements and strains are also considered. It is concluded that even when full similitude is not satisfied, it is possible to obtain valid results that can be extrapolated to predict prototype performance if one were interested primarily in the behavior of the asphalt layer. Preliminary analyses should be conducted, however, to guide on the selection of the model dimensions.
TL;DR: In this paper, the response of a G4(1S) strong post steel w-beam guardrail system to pendulum impacts has been investigated in a series of full-size physical tests and in simulated experiments using the explicit finite-element analysis code DYNA3D.
Abstract: The response of a G4(1S) strong post steel w-beam guardrail system to pendulum impacts has been investigated in a series of full-size physical tests and in simulated experiments using the explicit finite-element analysis code DYNA3D. The physical tests were conducted at the Federal Outdoor Impact Laboratory at the Turner Fairbank Highway Research Center of the Federal Highway Administration in McLean, Va. In the pendulum tests, an 880-kg mass was used to strike the rail perpendicular to its face. The rail section was attached to steel posts and blockouts and supported in a specially designed fixture. Initial velocities of the pendulum at impact were 9.25, 20, 30, and 35 km/h. Acceleration, force, velocity, and displacement histories of the impact event were obtained from accelerometer data taken during the testing. Data from the DYNA3D simulations of the impact tests compared well with the data obtained from the full-scale testing. Displacement plots of the deformed shapes of the rails at 25-ms intervals compared favorably with high-speed film images. Force versus displacement histories showed good agreement with those obtained from quasi-static experiments. The use of pendulum impact tests for screening and evaluation of alternative guardrail systems is recommended.
TL;DR: For instance, this paper found that more than 60% of trips for work in urban areas represent complex trip-chaining patterns, while females are more likely to use a simpler work trip pattern than males.
Abstract: This study examines the trip-chaining behavior of workers. It develops nine work-related trip-chaining patterns from the 1990 Nationwide Personal Transportation Survey data, based on the sequential link of activities occurring in a single day. The study finds that more than 60% of trips for work in urban areas represent complex trip-chaining patterns. Males are more likely to use a simpler work trip pattern than females. From the results of analysis of variance, there are gender variations between trip-chaining patterns in trip rates for nonwork activities, travel distance, and travel time. There are also significant gender differences in trip rates and travel resources in each trip-chaining pattern.
TL;DR: In this article, the authors define or reconstruct the track of a vehicle when passing the elements of a continuous curve (straight lines, circles) so the track (curve) suits all requirements to which transition curves must be adapted.
Abstract: Road and railway transition curves have again become the subject of important scientific research and serious traffic engineering analyses because of high driving speeds and demands for automatic drive (i.e., car pilots). This article shows, in an original way, how to define or reconstruct the track of a vehicle when passing the elements of a continuous curve (straight lines, circles) so the track (curve) suits all requirements to which transition curves must be adapted. The praxis whereby a known mathematical curve (e.g., a cubic parabola, lemniscate, or chlotoid) was assumed as a transition curve and its suitability was analyzed has been passed over. On the basis of assumed kinematics models of the motion of a vehicle along joint alignment elements with a changing radius of curvature, the writers have analyzed different transition curves resulting in safe, comfortable, and economic driving. The curve resulting from a parabolic velocity chart of front wheel rotation during such movement which found the most suitable has been named POLUSA; a geometrical analysis of POLUSA has been performed and a manual for practical use completed.