Showing papers in "Journal of Transportation Engineering-asce in 1991"

Nonparametric Regression and Short‐Term Freeway Traffic Forecasting

Abstract: After reviewing the problem of short-term traffic forecasting, a nonparametric regression method, the \Ik\N-nearest neighbor (\Ik\N-NN) approach, is suggested as a candidate forecaster that might sidestep some of the problems inherent in parametric forecasting approaches. An empirical study using actual freeway data is devised to test the \Ik\N-NN approach, and compare it to simple univariate linear time-series forecasts. The \Ik\N-NN method performed comparably to, but not better than, the linear time-series approach. However, further research is needed to delineate those situations where the \Ik\N-NN approach may, or may not be, preferable. Particular attention should be focused on whether or not regression methods, which forecast mean values, are appropriate for forecasting the extreme values characteristic of transitions from the uncongested traffic regime to the congested regime. In addition, larger data bases may improve the accuracy of the \Ik\N-NN method.

Realistic Simulation of Water Distribution System

Abstract: Due to financial constraints in developing countries, water supply to various consumers is quite less than actual demand. A technique for simulation of water distribution network duly considering this low supply situation is presented. This is accomplished by satisfying an additional constraint of head-flow relationship at each node. The conventional methods just give the resulting pressures at various nodes in the prescribed demand condition. This is meaningless in a low-supply situation. The proposed method gives actual supply quantity from each node based on inherent characteristics of the system. The practical advantages are also discussed.

Spectral Analysis of Highway Pavement Roughness

Abstract: This paper reports new findings in the spectral analysis of pavement roughness. Elevation profiles of federal and interstate highways were measured with a profilometer, and spectral analysis was used to compute power spectral densities for the longitudinal elevation of pavements. The longitudinal profiles obtained were also used to compute the International Roughness Index (IRI) using a quarter‐car simulation method. An extensive review of the existing techniques for pavement spectral analysis was done from which it was found that previously developed models do not explain pavement spectral properties very well, especially for long wavelengths in the spectral decomposition. A new equation that fits the power spectral density curves for several pavement types was developed. A set of models was also developed to predict the power spectral density as a function of pavement type and age, and the IRI.

Delphi study on bridge condition rating and effects of improvements

Abstract: As part of an effort to develop guidelines for appraising bridge improvement needs, a Delphi study was conducted to seek opinions from bridge inspectors and engineers in the Indiana Department of Transportation (INDOT). The specific objectives of the study were to: (1) Establish relationships between subjective bridge condition ratings and the FHWA's numeric ratings; (2) assess relationships between the subjective rating and the severity and extent of distresses; (3) find relationships between the numeric condition rating and the expected remaining service life of bridges; and (4) estimate the effect of improvements upon the numeric condition rating and expected remaining service life of bridge components. The perception of bridge condition and the interpretation of FHWA's numeric condition rating varied among the bridge inspectors. The Delphi rounds helped to evaluate the amount of variation and subsequently to decrease it. As for the remaining service life of bridges, results from the Delphi analysis an...

Delphi Methodology for Economic Impact Assessment

Abstract: In 1988, the Roads and Transportation Association of Canada (RTAC) funded a research project to provide a look at the road-funding situation in Canada, the parameters related to it, and its potential economic ramifications at the turn of the century. To do this, a Delphi forecasting approach was chosen, which looked at how the intensity of system use and the costs of building and operating the road system would change in the interval and identified technological, economic, and social factors that might affect road-infrastructure investment patterns in the future. This paper focuses on the methodology used in the study. The technique worked well, with good response levels from the panel members, reasonable response times, and convergence on the majority of questions within three rounds of questioning. Microcomputer technology was exploited to simplify older manual methods for processing such data. The technique offered significant advantages over quantitative forecasting through its ability to reach consensus on the validity of forecasts, basic assumptions underlying them, and potential key developments that might result in changes to them.

Older Drivers and Intersection Traffic Control Devices

Abstract: This paper examines the relationship between accidents of elderly drivers and intersection traffic control devices. The data was analyzed in two stages, and the analyses were performed using the induced exposure method, in which the exposure to an accident is defined as the probability of being the driver not cited for the accident occurrence. First the conditions under which elderly drivers have higher accident involvement were determined and then statistical tests were conducted to compare these conditions to the accident involvement of other drivers. The results indicate that the accident involvement of elderly drivers is higher than that of the other drivers under certain circumstances. This study documented the fact that the elderly experience difficulty as the complexity of the design and traffic control device application increases. To reduce the accident rates of elderly drivers and improve safety measures that affect them, modifications of the licensing testing and procedures and implementation of driver training programs for the elderly are suggested. Language: en

Traffic Conflicts in Expressway Merging

Abstract: The risk of collision in an expressway merging process is investigated using the traffic conflict technique. The severity of conflict in a merging event is quantified by a measure that is the inverse of the time measured to collision. To determine this measure, recordings of merging events were obtained at a merging area of an expressway in Singapore over eight periods, and the arrival times of vehicles at constantly spaced intervals were subsequently extracted in the laboratory. The errors in the data-collection process were minimized by using two video cameras simultaneously in the recording process to increase the size of images and playing back the tapes at a lower speed during data extraction. The systematic errors in the data due to observers' bias were also estimated to facilitate data adjustment. Based on the adjusted data, the computed measure from about 200 merging events in each observation period was found to be best fitted by the mixed Weibull distribution. Using the tail end of the distribution, the probability of near-accident per merge in each period was estimated.

Pavement performance and life-cycle cost analysis

Abstract: The current practice of life‐cycle cost evaluation for pavements does not take into account the differences in overall pavement serviceability performance among the alternatives considered. The solution derived from the evaluation may not be the most desirable to road users and the highway agency concerned. The need to consider pavement performance in assessing the merits of different design, maintenance, and rehabilitation strategies, together with the usual agency and user considerations, is highlighted. Two approaches for cost quantification of different pavement performance levels are suggested. One approach makes use of a quantitative performance measure, called the pavement‐performance quality index, to compare the different overall pavement performances of various strategies. The other approach relies on establishing a relationship between quantitative benefits and pavement serviceability values. For each approach, the analytical framework for incorporating pavement‐performance considerations into ...

Network Design Programming of U.S. Highway Improvements

Abstract: This paper describes a network design approach to the selection and programming of alternative route improvements to the U.S. highway network of interstates, four-lane urban highways, and principal rural arterials. Alternative route-improvement strategies are defined as mutually exclusive sets of link improvements that can be programmed for construction within any decade of a multidecade planning horizon. The two improvement strategies considered for each route are: (1) To make every link median divided with controlled access and at least four lanes; or (2) to make every link at least four lanes, but without any changes to median division of access control. The examples of this paper evaluate 536 potential improvements to 289 major highway routes between adjacent Bureau of Economic Analysis (BEA) regions, or nearly two improvement strategies per route. Route-improvement strategies programmed for each decade are constrained by 10-year funding allocations. A trip distribution model is used to distribute commodity shipments forecast for each decade among regions. Route-improvement benefits are computed as changes in the value of the objective function, which is the total discounted interregional shipment cost for all years of the planning period. Since different routes and interregional shipments can share common links, a rank-add-and-swap heuristic solution procedure was developed and applied that accounts for the interdependent costs and benefits of route improvements. Implications of this network design approach for planning future expansions and improvements of the interstate highway network are discussed.

Truck Movement and Access in Urban Areas

Abstract: This paper discusses ways in which trucks may be specifically incorporated in the planning, design, and operation of urban traffic facilities. It is argued that if traffic engineers were to take greater and more explicit recognition of the needs of trucks in traffic management, this would not only aid truck movements, and thus contribute to economic efficiency, but would also assist the movement of passenger vehicles, as well as contribute to broader goals related to such aspects as road safety and regional economic development. The paper provides practical guidelines, based upon the results of recent research, to assist the practicing traffic engineer. It includes a discussion of the objectives of truck‐oriented traffic management, a review of problems in urban trucking, on‐street and off‐street traffic management solution strategies for solving those problems, and information concerning truck trip generation.

Characteristics of Fixed‐Roadside‐Object Side‐Impact Accidents

Abstract: Each year approximately 160,000 people are involved in accidents where the side of a vehicle strikes a fixed‐roadside object such as a tree, utility pole, or guardrail. Of these 160,000 occupants, 60,000 are injured and 1,600 are killed. When a side‐impact accident with a fixed object occurs, an occupant has one chance in three that he will be injured and one chance in 100 that they will be fatally injured. This level of injury and death represents a loss to our society of $3 billion each year. Trees and utility poles are by far the most frequently struck objects, the objects that result in the highest risk of injury, and hence the objects causing the greatest loss to society. Data from the National Accident Sampling System and the Fatal Accident Reporting System are used to identify characteristics of this accident scenario.

Effects of Pavement Age and Traffic on Maintenance Effectiveness

Abstract: An evaluation of the effects of pavement age and traffic loading on routine maintenance effectiveness is presented. A conceptual framework for the evaluation was developed. Change in surface roughness was considered a measure of pavement surface deterioration. The conceptual framework was tested by using data on a selected number of pavement sections from the state highway system in Indiana. Regression models were developed to examine the effects of routine‐maintenance expenditure level, pavement age, and traffic loading on change in surface roughness. Routine maintenance effectiveness for pavements in fair or good condition was found to be higher than that for pavements in very good condition. In addition, the maintenance work involving premix leveling and seal coating was found to provide a relatively higher effectiveness than the work involving joint and crack sealing and patching.

Field effects of water pumping beneath concrete pavement slabs

Abstract: Water pumping beneath concrete pavement slabs is considered to be a major cause of pavement failure. The objectives of this work are to determine typical water pressures and velocities during pumping in the field as well as the effects of pressure, velocity, and thermal movement on erosion beneath slabs. The location of the water pumping is between the bottom of the concrete slab and the subbase. Field tests indicate that vehicle traffic produces high pressures beneath the second slab and suction pressures beneath the first, which induces water velocities in the opposite direction of vehicle motion. Field tests on Florida's Interstate 10 reveal pressure differences as high as 70 kPa, which produce velocities up to 0.9 m/s in the opposite direction of vehicle motion. Water pumping is more severe at the corner of the second slab and during upward thermal curling. Water movement may not be sufficient to cause subbase erosion based on this limited field data. The daily expansion‐contraction cycle is shown to ...

Use of FWD Data for Pavement Material Characterization and Performance

Abstract: Conventionally used FWD backcalculation and pavement stress-strain computation procedures are based on linear static layered elastic theory. This paper presents a simple hypothetical case study in which the applicability of the assumptions made in the foregoing procedures is investigated using the finite-element method. The pavement displacements computed using static/dynamic falling-weight deflectometer (FWD) loading and constant and stress-dependent material properties were used as input for the backcalculation analysis. The assumed and backcalculated layer moduli were compared. The backcalculated asphalt concrete (AC) moduli values were within acceptable limits for all pavement sections studied except for the case of the thin AC pavement with a shallow rigid base. The subgrade moduli were consistently underpredicted; the base course moduli were both underpredicted and overpredicted. Widely used traffic-induced pavement strains that are related to pavement performance that were obtained under different loading and material property characterizations were also compared. Results indicate that the conventional procedures are not conservative, especially for thick AC pavement sections.

Evaluation of errors in automated pavement-distress data acquisition

Abstract: The extent of degradation and decay of transportation infrastructure has created new demands on maintenance management systems. This, in turn, has emphasized the need for accurate condition assessment data for use in infrastructure management. At the same time, technological advances in automated inspection systems provide the opportunity to automate the collection of surface condition data. The effect of the technology on accuracy has not been previously evaluated. This paper evaluates the data-acquisition component of two automated optical technologies and identifies the main sources of error. Simulated longitudinal and transverse cracks are used to illustrate the results. The simulations indicate that correction factors are important to compensate for errors due to resolution and coverage limitations. Therefore, on a crack-by-crack basis, most technologies will perform poorly. When cracks are uniformly distributed, equipment with high resolution but poor coverage provides more accurate estimates of cracking extent but has more variability than equipment with good coverage. Finally, the results indicate that the inherent variability in the location, width, and length of cracks may lead to significant error.

Traffic Assignment in Practice: Overview and Guidelines for Users

Abstract: This paper presents an overview of the elements of traffic assignment and a synthesis of the problems that may be encountered in applying traffic-assignment models in practice. The elements include preparing the transportation network, establishing the origin-destination (OD) demands, identifying a traffic-assignment technique, calibrating and validating a model, and forecasting. The practical problems of traffic assignment are classified into four categories: network-representation problems, system-subarea data-translation problems, model-calibration problems, and forecasting problems. The paper presents the state of the art in traffic-assignment elements and provides specific guidelines on their implementation in practice and on the resolution of the identified problems. This paper is one of a series being produced by the Urban Transportation Division (UTD) Transportation Planning Committee of ASCE.

Centralized Hub‐Terminal Geometric Concepts. I: Walking Distance

Abstract: This paper analyzes and compares several airporthub passengerterminal layouts in terms of average total walking distance. A second paper extends the results to include baggagehandling operations. F...

Aspects of Highway Superelevation Design

Abstract: The method of calculating superelevation in highway curves and its effects on vehicle dynamics and safety is of great importance in highway design. United States and German guidelines' relevant methods are presented and compared in this paper. The main differences between these two methods are related to design and operating speed concepts and their use to calculate superelevation for curve radii exceeding the absolute minimum. Some modifications to the current AASHTO superelevation design approaches are proposed, based on the relationship between the degree of curve and actual operating speeds, to harmonize highway superelevation design with drivers' actual speed behavior, which could enhance highway safety.

Climatic Considerations in New AASHTO Flexible Pavement Design

Abstract: This research is undertaken to study and assess carefully the effect of climatic factors on the new American Association of State Highway and Transportation Officials (AASHTO) design for flexible pavements Climatic factors considered include seasonal changes in the subgrade moisture content and the annual variations in the ambient temperature Through a sensitivity analysis of the new AASHTO equation, the change in the structural number required to offset a reduction in the subgrade resilient modulus due to an increase in moisture content is evaluated; an adjusted structural number is thus calculated The impact of the ambient temperature on the asphalt-concrete layer is evaluated by considering the interactive result of temperature and fatigue damage; the concept of weighted effective dynamic modulus is thus used A rational method is proposed to select the appropriate asphalt grade to minimize both low-temperature cracking and rut depth By knowing the asphalt grade and the mix properties, the weighted, effective asphalt-layer coefficient is calculated An example to illustrate how climatic considerations can be incorporated into the AASHTO design is presented

Climatic consideration in new asshto flexible pavement design

Abstract: The new AASHTO design for flexible pavement provides the basic structural design model (equation presented). In this study, the effect of subgrade moisture on the structural number via resilient modulus is quantified through a sensitivity analysis of the AASHTO equation. The study also evaluated the impact of air-temperature variation on the asphalt-layer resilient modulus, thereby introducing the effective asphalt-layer coefficient concept. A rationaL method is presented by which the asphalt-concrete grade can be selected.

Knowledge Base on Semi‐Actuated Traffic‐Signal Control

Abstract: The efficient use of semi-actuated signal control requires careful selection of phasing plan, timing design, and detector configuration. Computer simulation can be used to assist in the search for efficient ways of operating such a control, but it has not been widely employed by practicing engineers. Analytical methodology for preoperational design of signal control are potentially easier to use than are simulation models. Their development, however, has not reached a mature stage. The objective of this study is to use a simulation model to develop an easily accessible knowledge base for the use of semi-actuated control at individual intersections. This knowledge base concerns semi-actuated operations that rely on inductive loop detectors for presence detection of vehicles and that do not accommodate pedestrian timing. It focuses on the following aspects of the signal operations: choice of phasing plan, timing design for nonactuated phase and actuated phase, timing setting of call-delay for delayed-call detectors, and the choice between semi-actuated and full-actuated control.

Remaining-life consideration in pavement overlay design

Abstract: The thickness deficiencybased approach is a widely used procedure for pavement overlay design. There is a need to incorporate a remaininglife consideration into this approach. The traditional thick...

Use of Gravel Properties to Develop Arrester Bed Stopping Model

Abstract: This study was undertaken to investigate the engineering properties of a river pea gravel and to develop a model that can be applied to predict the stopping distance of runaway trucks in arrester b...

Impact of Natural Site Variability on Nondestructive Test Deflection Basins

Abstract: A series of nondestructive tests (NDT) using a falling‐weight deflectometer and Dynaflect was performed at 20 test locations in Arizona. Deflection basins were obtained at 10 ft (3 m) intervals over 90 ft (27 m) length of highway. A statistical analysis of site variability, based on NDT test data, was conducted. The variability in deflection basins was found to result primarily from spatial variability of the subgrade materials. Results from cone penetrometer tests conducted at NDT test locations showed considerable spatial variability of subgrade materials both vertically and horizontally. Variation in pavement system response resulting from pavement and subgrade material stress‐level‐induced nonlinearities was found to be insignificant. Recommendations for assessing the significance of natural site variability are made, and a procedure for selecting analysis sections for overlay design purposes is suggested. A technique is also suggested for selecting length of test sections for NDT that takes into cons...

Centralized hub-terminal geometric concepts. II, Baggage and extensions

Abstract: This paper shows how the geometric concepts examined in the first paper perform for baggage operations, recognizing that passengers and bags travel different distances through the airport. The paper shows that the most effective geometry (minimizing total passenger walking plus baggage travel costs) can be selected by focusing on passenger walking alone, provided that one first calculates an equivalent percentage of transfers with a simple formula. The paper also introduces a “sun” terminal concept, consisting of a circular concourse (open or closed) with both gates and piers (possibly with branches), which generalizes the geometries of part one to some advantage. Finally, the paper introduces and compares the results of two techniques that are useful for more refined analyses. The first of these, calculus of variations, was used to develop simple approximate formulae for the optimal shape of parallel-pier terminals. The second technique, simulated annealing, does not lead to formulae but can be used without simplifications; e.g., to refine a preliminary design with the aid of a computer, recognizing real-world complications.

Development of Prototype Expert System for Roadside Safety

Abstract: Collision of vehicles with fixed objects adjacent to the roadway has been a concern of traffic engineers for many years. One solution to prevent or reduce the number of accidents of this type is to install a traffic barrier to shield the objects from being hit directly. However, because the barrier itself is a fixed object, the question is whether a barrier is more effective at a particular location than no barrier at all. If a barrier is needed, where should it be located and what type of barrier would satisfy the design criteria? Issues of this nature are ill‐structured and difficult to address using normal computing technology since many factors contribute to the problem. For roadside safety, the primary factors are diverse and interrelated. This paper presents a demonstration prototype knowledge‐based expert system (Roadside) for roadside‐safety analysis. In particular, this system is developed to evaluate whether a traffic barrier is necessary for a particular site in analysis. Development of this de...

Evaluation of outside and inside expressway ramps based on merging probability

Abstract: Japanese urban expressway networks contain not only the usual outside ramps, but also many inside ramps. Although the inside ramps do not block off adjacent and always‐expensive urban property, the design is less desirable operationally than one with outside ramps. This report describes a mathematical method to evaluate which of the two on‐ramp designs is better in terms of merging probability. Knowing the probability allows us to evaluate the operating conditions and capacities at merging area. A series of traffic surveys are conducted to accumulate data on the traffic‐flow characteristics of outside and inside ramps on the Hanshin Expressway network in Kobe, Japan. The headway distribution on the through lane and the acceptable gaps of the merging vehicles were measured from video tapes. The merging probabilities are calculated using those survey results. The results indicate higher merging probability for the outer parallel type. It is suggested that the inside‐ramp merging‐lane length should be longer...

Toward intelligent traffic signal design system

Abstract: A framework for an intelligent traffic signal design system, incorporating both expert system technology as well as conventional programming techniques, is presented. This system will help less trained engineers and traffic personnel achieve optimal traffic signal designs by closely mimicking the design process of experts in the field. As the first stage of development, an expert system is evolved to suggest phase plans for intersections to be signalized. The representation of the knowledge and the strategy used to arrive at phasing patterns are discussed.

Effects of horizontal-curve transition design on truck roll stability

Abstract: The intent of this article is to provide information that will facilitate the design of roads that are safer for heavy trucks, which have a greater tendency to roll over than passenger cars. The roll performance of tractor-semitrailer trucks on horizontal curves with three different types of transitions is investigated using computer simulation, and the results are used to develop guidelines for horizontal-curve transition design. The roll dynamics of a truck traveling on a transition and a superelevated curve are described, and the effect of superelevation on the rollover threshold of tractor-semitrailer trucks is also discussed. Three evaluation parameters (roll stability margin, acceleration overshoot, and critical speed) are proposed and used in evaluating different transition types. Three types of transition are investigated: one in which 2/3 of the maximum superelevation is developed before the start of the curve; one in which the superelevation is fully developed at the start of the curve; and one in which superelevation is developed in a short spiral section. A test matrix consisting of different truck speeds, different radius curves, and different transitions is used. The spiral transition is shown to be most desirable type of transition.

Testing, verification, and validation of expert systems

Abstract: This paper discusses how an expert system can be tested, verified, and validated. A prototype expert system, the Hazardous Location Analyst (HLA), which analyzes high‐accident locations, is used to illustrate the evaluation process and to examine the various aspects of testing, verification, and validation. Identified were several key issues that must be addressed when evaluating an expert system: problem complexity, no “correct answers,” the problem of defining expert‐level performance, and considerations in knowledge‐base refinement. The paper also suggests ways in which to make comparisons between expert‐system and human‐expert inferences so that ease of use, knowledge‐base adequacy, and completeness may be examined. The paper further suggests that although some quantitative performance measures are useful for the evaluation process, a qualitative evaluation is perhaps also appropriate for many aspects of these kinds of systems.