Showing papers in "Journal of Transportation Engineering-asce in 1996"
TL;DR: In this article, a negative binomial regression of the frequency of accidents at intersection approaches is proposed to estimate the accident reduction benefits of various proposed intersection improvements on operationally deficient intersections.
Abstract: Traffic accidents at urban intersections result in a huge cost to society in terms of death, injury, lost productivity, and property damage. Unfortunately, the elements that effect the frequency of intersection accidents are not well understood and, as a result, it is difficult to predict the effectiveness of specific intersection improvements that are aimed at reducing accident frequency. Using seven-yr accident histories from 63 intersections in Bellevue, Washington (all of which were targeted for operational improvements), this paper estimates a negative binomial regression of the frequency of accidents at intersection approaches. The estimation results uncover important interactions between geometric and traffic-related elements and accident frequencies. The findings of this paper provide exploratory methodological and empirical evidence that could lead to an approach to estimate the accident reduction benefits of various proposed improvements on operationally deficient intersections.
586 citations
TL;DR: This paper presents a method for estimating freeway travel times in real time directly from flow measurements, which is desirable for present and future Intelligent Vehicle-Highway Systems applications and has potential applicable to automatic traffic control and automatic incident detection.
Abstract: This paper presents a method for estimating freeway travel times in real time directly from flow measurements, which is desirable for present and future Intelligent Vehicle-Highway Systems (IVHS) applications. An inductive modeling approach adapted here is based on stochastic queuing theory and the principle of conservation of vehicles. The analytical expression for link travel times satisfies traffic dynamics where the new form of the conservation of vehicles has been derived under generalized traffic conditions. A computer program has been developed to implement the algorithm. Analysis results show that the estimates have good agreement with empirical data measured at 30-s intervals. This methodology has potential applicable to automatic traffic control and automatic incident detection.
109 citations
TL;DR: The development of a computer model based on genetic algorithms, an optimization tool capable of overcoming combinatorial explosion, to solve the pavement maintenance-rehabilitation trade-off problem at the network level is described.
Abstract: This paper describes the development of a computer model (known as PAVENET-R) based on genetic algorithms, an optimization tool capable of overcoming combinatorial explosion, to solve the pavement maintenance-rehabilitation trade-off problem at the network level. The formulation of the PAVENET-R model is described in detail. An integer coding scheme is selected for parameter representation in the model. Two genetic-algorithm operators, namely the crossover operator and the mutation operator, are used. A “change table” encodes constraints to the genetic-algorithm operations to ensure that only valid offspring are generated from a parent pool. Four numerical examples of road networks of 30 pavement segments, each with different relative costs of rehabilitation and maintenance activities, are analyzed to demonstrate the trade-off relationship between pavement rehabilitation and maintenance activities. The detailed maintenance and rehabilitation schedules of the solutions, and the convergence characteristics of each solution are presented.
109 citations
TL;DR: In this paper, an experimental program was carried out to investigate the influence that a geogrid has as reinforcement for the granular base layer of a flexible pavement constructed on sand, and two different mechanisms that reduced the permanent deformation of the pavement (rutting) were recognized.
Abstract: An experimental program was carried out to investigate the influence that a geogrid has as reinforcement for the granular base layer of a flexible pavement constructed on sand. Tests were performed using a model testing facility that allowed repeated passes of a tire across a section of pavement that was either unreinforced or reinforced with a geogrid. Measurements were taken of the surface deformations and of internal movements in the pavement and subgrade, and these were used as a means of assessing any improvement in pavement performance due to the inclusion of the geogrid. Two different mechanisms that reduced the permanent deformation of the pavement (rutting) were recognized. They were a significant reduction in the deformation of the base layer due mainly to the confinement and interlocking of the base material, and the improved load distribution on the subgrade layer that causes a reduction of subgrade deformation. Both single- and multiple-track tests were performed. It was found that in both cases, for a thin base layer, the least surface deformation was obtained with the geogrid at the center of the base layer.
73 citations
TL;DR: Investigators found that AADT estimation errors are very sensitive to the assignment effectiveness, which indicates that highway agencies should put more emphasis on sample site assignments to correct ATR groups than on the duration of count.
Abstract: Investigators examined the statistical precision of annual average daily traffic (AADT) estimates derived from short period traffic counts (SPTC). Many automatic traffic recorder (ATR) sites located on Minnesota's highway system are studied. Effects of various factors on estimation errors are explored. The appropriateness of volume adjustment factors is expressed in terms of assignment effectiveness, which mirrors the degree of correctness with which a sample site is assigned to an ATR group. Investigators found that AADT estimation errors are very sensitive to the assignment effectiveness. Study findings indicate that highway agencies should put more emphasis on sample site assignments to correct ATR groups than on the duration of count. By analyzing ATR data from two Canadian provinces--Alberta and Saskatchewan--the findings are confirmed. Highway agencies may find the material presented in this paper beneficial in the rationalization of their traffic volume counting programs.
71 citations
TL;DR: In this article, the effect of temperature variation on plain-jointed concrete pavements is studied using a finite-element model consisting of four slabs separated by longitudinal and transverse joints, where the interaction between ground and the concrete slab along with interaction at the joints were modeled using interface elements.
Abstract: The finite-element study of the effect of temperature variation on plain-jointed concrete pavements is presented. Temperature variation causes curling and thermal-expansion stresses. Curling stresses result from temperature gradients through a slab depth. Thermal-expansion stresses are induced due to uniform changes in temperature that cause the slab to expand. The developed three-dimensional (3D) model consists of four slabs separated by longitudinal and transverse joints. The interaction between the ground and the concrete slab along with interaction at the joints were modeled using interface elements. These elements gave the model the capability to solve for partial contact between curled slabs and the ground to investigate the effect of compressive stresses that may develop at the joints during curling, and to study the influence of friction between slabs and the ground. The data obtained using the finite-element model has shown reasonable agreement with the results obtained from three computer models: KENSLABS, ILLI-SLAB, JSLAB, and the analytical solution proposed by Bradbury. The best correlation was obtained with JSLAB. The model was used to perform parametric studies on curling and thermal-expansion stresses to study the effect of superposition of both stresses and to address the effect of uniform temperature changes on joint opening. Another simpler model using nine layers across the depth of a pavement slab was used to introduce the effects of nonlinear temperature distribution. The results of parametric studies are presented and compared with other solutions. The arithmetic addition of positive curling stresses and thermal-expansion stresses were less than those stresses obtained by superposition. In some cases, the calculated joint openings were higher than the allowable joint opening. Nonlinear temperature distribution caused higher tensile stresses than the linear distribution of temperature. The difference in tensile stresses between the two distributions was approximately 3–13% of the modulus of rupture of concrete.
64 citations
TL;DR: In this article, the authors examined composition, weather, and time-of-year count variability for a longitudinal bicycle count program and proposed a new bicycle functional classification system based on PM peak-period composition.
Abstract: This research examines composition, weather, and time-of-year count variability for a longitudinal bicycle count program. The results indicate greater variability in the PM peak period than in the AM peak period, and this variability is at least partially attributable to the presence of nonutility cyclists. Second, all locations display the same functional form for count volume by both temperature and amount of precipitation, and it appears that temperature may be a better predictor of volume than the amount of precipitation for these data. Third, the results of a Poisson model statistically confirm many of the factors thought to influence cyclists, and identify that a single count volume may be biased by as much as ±15% depending on the time of year in which the count was undertaken. Finally, a new bicycle functional classification system based on PM peak-period composition is proposed.
46 citations
TL;DR: In this article, the authors provided a comprehensive and detailed estimation of traffic delay due to a freeway workzone where the roadway in one direction is closed and the traffic usually on the closed roadway is diverted to share the road in the opposite direction.
Abstract: Vehicle delay is one of the most serious impacts of highway workzones on existing traffic operations. The present study provides a comprehensive and detailed estimation of traffic delay due to a freeway workzone where the roadway in one direction is closed and the traffic usually on the closed roadway is diverted to share the roadway in the opposite direction. The total delay was decomposed into speed reduction delay and congestion delay. Different procedures were developed to estimate speed reduction delay for several roadway conditions. A mathematical model was developed to find the length of the queue upstream of a workzone and a procedure was generated to estimate daily congestion delay under any given condition. Alternative roadway closure patterns along the length of a given project were evaluated in terms of traffic control cost and additional road user costs. The optimal workzone length for a given project was studied. Procedures were developed to determine the optimal workzone length.
41 citations
TL;DR: In this article, a critical review of pertinent research and related provisions in the design guidelines of the United States, Germany, and Great Britain is carried out in this paper, and shows that, although a variety of highway-design assessment methods with respect to the aforementioned research areas have been suggested in literature, the relevant findings have not yet been satisfactorily incorporated into highway design guidelines.
Abstract: Research of human factors in highway engineering may be seen to include two main areas: the effect of geometric design on driver behavior, and the consideration of driver behavior variability. A critical review of pertinent research and related provisions in the design guidelines of the United States, Germany, and Great Britain is carried out in this paper, and shows that, although a variety of highway-design assessment methods with respect to the aforementioned research areas have been suggested in literature, the relevant findings have not yet been satisfactorily incorporated into highway design guidelines. On the basis of the aforementioned research findings and existing guidelines' provisions, a framework is discussed that allows for the consideration of “nondesign” road users, such as older drivers, and also incorporates checks for the overall safety of design as a feedback loop in the design process.
34 citations
TL;DR: In this article, a new asphalt layer modulus degradation model for use with flexible-pavement analysis procedures is described, which is capable of determining the reduction in stiffness of the asphaltic material in a flexible pavement due to cumulative fatigue damage.
Abstract: A new asphalt layer modulus degradation model for use with flexible-pavement analysis procedures is described. The model is capable of determining the reduction in stiffness of the asphaltic material in a flexible pavement due to cumulative fatigue damage. Measured surface deflection bowls from a number of test pavements are used with a pavement parameter back-calculation procedure, to determine the reduction in stiffness of the asphaltic material throughout the life of the pavement. Results show an exponential relationship between the reduction in asphalt layer stiffness and cumulative fatigue damage. This type of relationship does not agree with an earlier theoretical continuum damage mechanics model, where the relationship between the reduction in asphalt layer stiffness and cumulative fatigue damage was predicted to be linear.
33 citations
TL;DR: In this paper, the spectral and statistical characteristics of actual road surface elevation records are discussed, and the deviation of the road profile distribution from the Gaussian distribution is revealed, and it is shown that roads of different roughness seem to retain their spectral shape.
Abstract: The power spectral density (PSD) estimate is a parameter commonly used to characterize the acceleration of vehicles and, in conjunction with closed-loop random vibration controllers, to simulate the transport environment. The vertical acceleration experienced by the loading tray of road transport vehicles is mainly a function of the type of suspension, load, vehicle speed, and road surface characteristics. While the first three parameters may vary considerably between and during journeys, the statistical parameters used to describe road surface profiles are much less susceptible to change with respect to time. This paper presents a brief analysis and discussion of the spectral and statistical characteristics of actual road surface elevation records. The deviation of the road profile distribution from the Gaussian distribution is revealed, and it is shown that roads of different roughness seem to retain their spectral shape. In addition, a range of statistical parameters are introduced and recommended for use in the classification of road profiles. A technique in which a random vibration controller is used to simulate road profile spectra by controlling the displacement instead of the acceleration of a shaker table is demonstrated. The technique uses a physical model of a vehicle suspension to account for the dynamic characteristics of the vehicle. Finally, the use of digital signal processors (DSP) together with a time domain adaptive filter control technique for the accurate reproduction of synthesized demand signals is presented.
TL;DR: An algorithm and strategy for transit providers to find best alternatives for the user, and how a geographic information system can be used in the development of transit advanced traveler information system (TATIS) to meet these needs are developed.
Abstract: The trip making process using transit versus private automobile differs in the use of time schedules, walking paths, transfer stops, plus issues such as fare and safety. Due to these factors, many of the standard shortest path algorithms do not apply. The purpose of this study is to develop an algorithm and strategy for transit providers to find best alternatives for the user, and to demonstrate how a geographic information system can be used in the development of transit advanced traveler information system (TATIS) to meet these needs. This paper presents a short introduction to TATIS systems, some commonly used algorithms in determining the shortest and multiple paths, and a new strategy that was developed in this study which differs from standard network algorithms. The major features of this proposed algorithm are: (1) Capability of handling multiple modes of transit; (2) providing paths that include walking distances from and to the transit path as well as between transfer points; and (3) provision of multiple optimal paths to allow the user flexibility in choosing a path.
TL;DR: In this article, the probit and logit models are compared from an analytical point of view, whereas the probits model has more relia... and the logit model is superior to probit from the analytical point-of-view.
Abstract: Logit and probit models are statistical tools that are well suited to analyze modal split situation. Logit is superior to probit from the analytical point-of-view, whereas the probit has more relia...
TL;DR: In this article, the effect of rest periods on the fatigue response of asphalt concrete mixtures due to repeated loading applications by using linear elastic fracture mechanics and Schapery's theory of viscoelastic media crack growth was studied.
Abstract: The purpose of this research is to study the effect of rest periods on the fatigue response of asphalt concrete mixtures due to the repeated loading applications by using linear elastic fracture mechanics and Schapery's theory of viscoelastic media crack growth. The results of a series of third-point bending tests indicated that the two fatigue damage properties K1 and K2 were in good agreement with those of the theoretical prediction having the expression of the constant values of failure zone size and fracture energy in the crack growth. Specimens with low temperature and asphalt content of 0.5% more than optimum content exhibited longer fatigue life due to the higher stiffness in the mixtures. Besides, the number of repetitions to failure increased with the rest period and was more significantly exhibited at higher temperature.
TL;DR: In this article, a mechanistic-probabilistic vehicle operating cost (PVOC) model was developed to estimate vehicle operating costs of different vehicles operating on different roads in Saskatchewan conditions.
Abstract: In the face of an aging road infrastructure and shrinking highway maintenance budgets, optimizing the allocation of limited highway resources is paramount to the Saskatchewan Department of Highways and Transportation (SHT). In order to make informed infrastructure management decisions, SHT have identified the need to accurately quantify vehicle operating costs on different roads in diverse operating conditions. SHT had previous experience with the HDM III model, but found they could not support HDM III because of the extensive data requirements. As a result, in 1991 SHT initiated a review of available road user cost models in the hope of identifying a model that would meet the specific needs of SHT. No such model was found primarily because accurately predicting vehicle operating costs on most Saskatchewan roads is difficult because of the inherent uncertainty associated with the parameters that influence vehicle operating costs. Therefore, a mechanistic-probabilistic vehicle operating cost (PVOC) model was developed to estimate vehicle operating costs of different vehicles operating on different roads in Saskatchewan conditions. The PVOC model computes a probabilistic estimate of vehicle operating costs, including the expected value and the associated uncertainty of the estimate. The PVOC model was validated for several vehicle types operating on Saskatchewan roads and was found to be within 20% of published industry averages and within 9% of historic Saskatchewan truck fleet data.
TL;DR: In this paper, the authors examined the use of Pasternak foundation model in the analysis of load-induced concrete pavement deflections and bending stresses, as well as thermal stresses caused by warping of slabs.
Abstract: This paper examines the use of Pasternak foundation model in the analysis of load-induced concrete pavement deflections and bending stresses, as well as thermal stresses caused by warping of slabs. Using theoretical solutions developed by the authors for structural responses of slabs supported on Pasternak foundation, predicted slab deflections and bending stresses are computed and checked against actual field data. The field data, containing pavement responses under applied loads and thermal gradients respectively, are obtained from the results of full-size slab experiments reported in the literature. Satisfactory slab deflection and bending stress predictions by the Pasternak solutions can be obtained by calculating subgrade shear modulus as the product of modulus of subgrade reaction and a coefficient θ. With reference to actual field measurements, the analysis in this study indicates that using a constant θ value of 0.35 m 2 in the proposed Pasternak foundation model would achieve 1 to 25 improvements...
TL;DR: An analytical framework for developing econometric models is presented and postfact analysis is used to test the accuracy of the models, suggesting that simple models with few independent variables perform as well as more complicated and costly models, and that external factors have a pronounced effect on air-travel demand.
Abstract: Air-transport demand forecasting constitutes an important determinant of airport planning, design, and operations. Errors in forecasting can be very costly. Underestimating demand may lead to increased congestion, delay, and inadequate airport facilities. Overestimating demand may also create serious economic problems for airport authorities. It is, therefore, very important for airport planners to develop reliable forecasting models and to understand possible limitations in the forecasting accuracy of these models. The objective of this paper is to examine the predicting ability and forecasting accuracy of air-travel demand models. In particular, an analytical framework for developing econometric models is presented and postfact analysis is used to test the accuracy of the models. Statistical data describing air-travel demand patterns for two major international airports, the Frankfurt and the Miami International Airports, are used to demonstrate the effectiveness of the proposed models. In addition, the effect of external factors such as the deregulation of the air-transport industry is examined. The results suggest that simple models with few independent variables perform as well as more complicated and costly models, and that external factors have a pronounced effect on air-travel demand.
TL;DR: In this paper, a binary logit model was used to model the mode choice of different groups of travelers in Tiruchirapalli, Tamilnadu state, India.
Abstract: A knowledge of the rip characteristics of different groups of travelers in an urban area is of great use in planning land use and transport-related facilities. Travelers in households without vehicles (not even bicycles) make their trips either by walking or by using public transport. The mode choice of this group in Tiruchirapalli, Tamilnadu state, India is modeled for work trips using a binary logit model. Stratified mode-choice models are developed based on the location of the travelers' residence in relation to the central business district (CBD). The trip distance is identified as the major factor influencing mode choice. The critical trip length, which is defined as the limiting distance beyond which a traveler is not likely to make the journey on foot, is estimated for different subgroups of travelers using the probability models of mode choice. It is found that the acceptable walking distance for the different subgroups varies between 1.3 and 2.5 km.
TL;DR: In this article, a time-domain solution to the problem of viscoelastic pavement response under moving dynamic loads is proposed, which takes into account the variation of the dynamic load within the area of influence of the moving load at any particular location.
Abstract: This paper provides a time-domain solution to the problem of viscoelastic pavement response under moving dynamic loads. It assumes linear material behavior and uses Boltzman's principle to superimpose the effect of a loading function with time-dependent amplitude to the influence function of a pavement response parameter. The unique element of this formulation is that it takes into account the variation of the dynamic load within the area of influence of the moving load at any particular location. This formulation is applied in evaluating the effect of two suspension types, generically referred to as air and rubber. Dynamic load data for these suspensions was experimentally obtained with an instrumented vehicle. The accumulation of strain cycles along the road was translated into number of repetitions to fatigue failure assuming spatial repetitiveness of dynamic loads. Overall pavement section failure was defined as the number of repetitions corresponding to the 90th percentile of the subsection survival ...
TL;DR: In this article, the influence of shape and surface texture of coarse aggregates on the deformation characteristics of asphalt concrete mixtures was evaluated in the laboratory using fractal dimension analysis.
Abstract: The influence of shape and surface texture of coarse aggregates on the deformation characteristics of asphalt concrete mixtures was evaluated in the laboratory. Shape and surface texture of aggregates was measured using fractal dimension analysis. Seven different aggregate blends of the same gradation containing coarse aggregate from 100% uncrushed to 100% crushed were used to prepare the asphalt concrete mixtures. Measured properties of these mixtures included Marshall and Hveem stability as well as creep and permanent deformation. Fractal dimension analysis was shown to be a viable technique for characterizing aggregate particle shape and surface texture. Researchers found a direct correlation between permanent deformation of asphalt concrete mixtures and surface texture of coarse aggregate particles used in the mixtures. This is indicative that fractal dimension of aggregate particles used to prepare asphalt concrete mixtures is related to rutting and shoving in an asphalt pavement.
TL;DR: In this article, the dynamic response of concrete pavements subjected to moving loads is analyzed by using the 3D finite-element method in conjunction with Newmark integration scheme, where moving vehicle loads are modeled as lumped masses each supported by a spring-dashpot suspension system and having a specified horizontal velocity and acceleration.
Abstract: Dynamic response of concrete pavements subjected to moving loads is analyzed by using the three-dimensional (3D) finite-element method in conjunction with Newmark integration scheme The dynamic vehicle-pavement-foundation interaction effects are considered in the 3D finite-element algorithm The moving vehicle loads are modeled as lumped masses each supported by a spring-dashpot suspension system and having a specified horizontal velocity and acceleration Concrete pavements are considered to respond elastically and are represented by a series of brick elements The present formulation considers a linear viscoelastic foundation model (Kelvin model) consisting of a system of discrete linear springs and dashpots The interaction between concrete pavements and underlying soil foundation is considered The present results are compared with the available theoretical results to validate the accuracy of the present algorithm A study is conducted to evaluate the effects of various parameters on the dynamic response of concrete pavements subjected to moving loads
TL;DR: In this paper, a minimum risk route model was developed to determine minimum risk routes between an O-D pair by using population or environment risk units as link impedances, and the risk units for each link were computed by taking into consideration the probability of an accident and its consequences on that link.
Abstract: The objective of this study is to determine the minimum risk route for transporting a specific hazardous material (HM) between a point of origin and a point of destination (O-D pair) in the study area which minimizes risk to population and environment. The southern part of Quebec is chosen as the study area and major cities are identified as points of origin and destination on the highway network. Three classes of HM, namely chlorine gas, liquefied petroleum gas (LPG), and sulphuric acid, are chosen. A minimum risk route model has been developed to determine minimum risk routes between an O-D pair by using population or environment risk units as link impedances. The risk units for each link are computed by taking into consideration the probability of an accident and its consequences on that link. The results show that between the same O-D pair, the minimum risk routes are different for various HM. The concept of risk dissipation from origin to destination on the minimum risk route has been developed and dissipation curves are included.
TL;DR: A review of the evolution of a rigid pavement pumping model is presented in this article, where extensions were made to an existing model to consider the effects of climate and drainage conditions, as well as soil composition on pumping magnitudes.
Abstract: The efficient utilization of construction and maintenance resources requires the ability to effectively predict and model subgrade pumping in rigid concrete pavements. A review of the evolution of a rigid pavement pumping model is presented in this paper. Extensions were made to an existing model to consider the effects of climate and drainage conditions, as well as soil composition on pumping magnitudes. Additional modifications permit the effect of nonconventional vehicle configurations to be considered in the calculation of pumping values. Finally, the process of calculating pumping volumes and distributing void areas was altered to provide a more realistic effect. This improved model allows proposed designs to be analyzed to determine optimum pavement characteristics. The model is implemented in a finite-element-based method for analysis of pavements that also includes the effects of concrete cracking and fatigue. Urgent need for experimental data on the size and growth of voids beneath a pavement slab is pointed out.
TL;DR: In this paper, a closed-form back-calculation scheme called NUS-BACK was proposed for rigid-pavement evaluation, which can be used with deflections measured by any type of nondestructive surface deflection measuring devices directly.
Abstract: This paper describes the development of a solution of surface deflections for the problem of infinite-slab-on-elastic foundation and its use in back-calculation analysis. Numerical integration is employed to compute the surface deflections. The method adopted simplifies calculations and leads to easy application in back-calculation of rigid-pavement parameters. A microcomputer closed-form back-calculation program called NUS-BACK is developed for this purpose, using the surface deflections measured by nondestructive testing devices as input. A comparison is made between the proposed approach and a widely reported closed-form back-calculation algorithm called ILLI-BACK. The proposed closed-form back-calculation scheme presents a more general solution to the rigid-pavement-evaluation problem. NUS-BACK can be used with deflections measured by any type of nondestructive surface deflection measuring devices directly. A major advantage of NUS-BACK over ILLI-BACK is its superiority in handling deflection data with measurement errors. Numerical examples are presented to illustrate the differences between the two closed-form back-calculation solutions.
TL;DR: In this article, the authors presented a model to quantify the risk of delays to individual trains, as well as to specific track segments and to the schedule as a whole, which can be used to estimate the likely impact on reliability or arrival times, changes in train frequencies, and operating practices.
Abstract: This paper deals with the scheduling of trains so as to minimize train trip times while maximizing reliability of arrival times. The amount of risk of delay (RD) associated with a schedule is used as the reliability component of a constrained schedule optimization model. The paper outlines the model developed to quantify the risk of delays to individual trains, as well as to specific track segments and to the schedule as a whole. The risk model, which deals with single track operations, can be used to estimate the likely impact on reliability or arrival times, changes in train frequencies, and operating practices; track and station infrastructure investment strategies; and train technology upgrading. An application of the model to the optimization of schedules on a track corridor is described. The results obtained using the model are compared with the schedules used by train operations planning staff, in terms of overall delay and timetable reliability. The results highlight the significance of including a measure of timetable reliability, such as risk of delays, in the objective function for scheduling optimization.
TL;DR: In this article, an improved reliability model for predicting thermal cracking of asphalt pavements is presented, which accounts for the variability in the component design variables and the correlation between the two failure modes.
Abstract: Thermal cracking of asphalt pavements is a serious problem in Canada and the northern parts of the United States. On many occasions, either at the design stage or during service, highway agencies demand a forecast of pavement performance rating, which is highly sensitive to the intensity of cracking. There are two failure modes of thermal cracking: low-temperature cracking and thermal-fatigue cracking. Low-temperature cracking is caused by accumulated thermal stresses in the pavement layer during cold winters or spring thaws. Thermal-fatigue cracking is caused by daily cyclic thermal loading. Classical probabilistic approaches have been applied to pavement design systems, including thermal cracking predictions, during the past three decades. Advances in reliability analysis, however, have proven that classical reliability methods are inconsistent, and mandate that current design procedures should be revised accordingly. This paper presents an improved reliability model for predicting thermal cracking. The proposed model accounts for the variability in the component design variables and the correlation between the two failure modes. The model results were verified using Monte Carlo simulation, and the sensitivity of the predicted intensity of cracking to various design variables was examined.
Journal Article•
TL;DR: To improve performance of incident detection algorithms on I-4, the subsections were regrouped by two factors: horizontal alignment and presence of ramps and no significant difference in incident detection rate was found between these subsections.
Abstract: The potential improvement in incident detection can be achieved by examining the major factors that may influence incident rates and incident detection rates. The subsections of the central I-4 corridor were grouped by geometric characteristics including horizontal alignment (straight or curved) and vertical alignment (upgrade, level, or downgrade); and also by presence of ramps (on-ramps, off-ramps, or none). It was found that subsections with off-ramps have significantly higher incident rate and incident detection rate than subsections with on-ramps or with no ramps. It was also found that upgrade subsections have significantly higher incident rate than level or downgrade subsections. However, no significant difference in incident detection rate was found between these subsections. Based on the study results and to improve performance of incident detection algorithms on I-4, the subsections were regrouped by two factors: horizontal alignment and presence of ramps.
TL;DR: Turned-down guardrail terminal sections were analyzed using LS-DYNA3D, a dynamic, nonlinear, large deformation finite-element modeling package with capabilities for simulating vehicular impacts into roadside hazards.
Abstract: Turned-down guardrail terminal sections were analyzed using LS-DYNA3D, a dynamic, nonlinear, large deformation finite-element modeling package with capabilities for simulating vehicular impacts into roadside hazards. A baseline simulation was conducted on the existing turned-down approach terminal section, as well as on various retrofit options. Simulation findings were used to identify potential design changes and to select the two most promising options. Modified designs were subjected to six low-speed and one high-speed full-scale crash tests with a minisize automobile. The crash testing verified that one of the retrofit designs would allow the W-beam rail to drop down without causing vehicle rollover when impacted end on by a minisize automobile. However, the revised design did not meet recommended safety standards when one of the weakened posts failed to break away as designed. It is believed that by revising the post installation procedures, the modified turned-down terminal section would perform satisfactorily.
TL;DR: In this article, the optimal number of pumping stages for a multistage pipeline with constant friction factor has been investigated and a closed-form solution for a long pipeline with relatively flat topography has been provided.
Abstract: Long-distance pipelines transporting fluids against gravity and frictional resistance involve multistage pumping. Equations for the optimal diameter and the pumping head for a single-stage pumping main are available. However, in the case of multistage pumping, the optimal number of pumping stages are worked out by an enumeration process. Such a process does not indicate functional dependence of input parameters on the design variables. In this paper, the multistage pumping main design is formulated as a geometric programming problem having a single degree of difficulty. The constant friction factor case of the problem yielded a closed-form solution for a long pipeline with relatively flat topography. The variation of the friction factor with diameter has been accounted for iteratively.