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Computerization of heuristic-based decision-making problems in transportation engineering
Book Reviews This research effort is focused on the analysis of the unique characteristics of single-lane operations at signalized intersections, the development of a leftturn equivalent model which provides the basis for a capacity analysis methodology. The analysis is founded on the concept of the queue clearance time and the principle that single-lane approaches should not be viewed individually but rather in tandem with the opposing approach. The parameters utilized in the predictive equations were based on information provided from individual cycles rather than 15minute periods. The proposed general procedure is a three-step process. The first step involves the calculation of the ideal queue clearance time from an exponential model, while the second step involves the introduction of the adjustment factors incorporated in the 1985 Highway Capacity Manual (HCM) for estimating prevailing queue clearance time. The third step involves the calculation of the left-turn equivalent, based on variables reflecting the relative friction of the subject approach. The predictive equations proved to be useful not only for a microscopic analysis, but for a macroscopic one as well. Furthermore, the methodology can be applied in both operational and design capacity analysis.
Analysis of traffic spatial shift resulting from optimal signal timing and special generators. Dikun, Suyono, Ph.D. The University of Wisconsin-Mu&son, 1988. 241 pp. Supervisor: Robert L. Smith, Jr. Order Number DA8903274 Traffic spatial shift as a result of traffic signal optimization in an urban corridor was investigated based on both the existing condition and potential future conditions with higher travel demand. The impacts of this spatial shift on the optimal signal timing, and vice versa, was analyzed through an iterative application of a traffic signal optimization model and a traffic diversion model. TRANSYT7F was used to optimize the signal system in the corridor network and to estimate overall traffic performance, including route travel times. A simple traffic diversion model developed from a logit choice model was chosen to represent the aggregate response of travelers to the choice situation. An algorithm for the interaction of TRANSYT7F and the diversion model was developed so that traffic equilibrium can be reached quickly. The initial optimization of signal timing created differences in travel time on alternative routes of 5 %6%. The iterative application of the traffic diversion model followed by simulation of the new flow conditions with TRANSYT-7F resulted in changes in link flow levels of l %-3 %. The new traffic flow conditions at equilibrium, however, did not significantly
45
affect the overall network measures of effectiveness (MOEs). Subsequent reoptimization of the signal timing based on the new link flow levels followed by traffic diversion to reach equilibrium resulted in only a 1% reduction in the performance index (PI) after the third optimization. Incremental expansion of the base outbound flows by 10X-30% was used to model the potential impacts of special generators on signal timing and spatial shift. In contrast to the base flow simulation, the performance of the network with the higher flows declined (higher PI) by 2%-8% in reaching equilibrium. Subsequent reoptimization resulted in improvements in the PI at equilibrium of up to 5 % . For the highly limited range of network, traffic signal, and flow conditions examined in this research, a reoptimization may be warranted if the travel time differences exceed 15 % in both directions.
Computerization of heuristic-based decisionmaking problems in transportation engineering. Faghri, Ardeshir, Ph.D. University of Virginia, 1989. 292 pp. Order Number DA9002842 This study investigates the potential applications of knowledge-based expert systems in transportation engineering. The three major topics covered are: (i) A description of the fundamental concepts of knowledge-based expert systems and how they relate to transportation engineering. The general differences between expert systems and conventional computer programs are summarized, and the process of transferring knowledge from human experts to computers is described. The architecture of knowledge-based expert systems is shown to separate the knowledge of the problem domain (knowledge base) from general problem solving (inference engine). Different approaches to each of these tasks are described and recent applications to several transportation engineering problems are presented. (ii) The selection of appropriate representation techniques for different classes of transportation engineering problems. Three of the most commonly used techniques for representing knowledge in the knowledge base of knowledge-based expert systems are described; and the highlights, shortcomings, and applications of each technique are explained. This section focuses on an examination of the significance of the means of representing the knowledge base in the development of knowledge-based expert systems, with special reference to five classes of transportation engineering problems-planning, operations and control, design, construction and maintenance, and management and finance. Under each class, one or two transportation and traffic problems suitable for knowledge-based expert systems development are briefly described, and the most suitable representation technique(s) for their development is recommended. (iii) A descrip-
Book Reviews
46
tion of the development of one transportation engineering problem chosen from the previous section. The stages required in the development of a knowledge-based expert system -problem identification, conceptual analysis, formalization, implementation, and evaluation- for the chosen problem are described in detail.
Control of freeway traffic flow. Smulders, Stef A., Dr.ing. University 1989. 162 pp.
of i%ente
(Netherlands),
In this thesis, a freeway traffic control problem has been addressed and solved. The control problem consists of designing an optimal policy for the variable speed signs of the Dutch Motorway Control and Signalling System. The aim is to reduce the instabilities of traffic flow that occur if demand is high, and thereby to reduce the probability of congestion and increase safety. For the design of an optimal control policy, we proposed a criterion which measures the expected total throughput of a freeway section until the moment of congestion. Based upon the policies obtained with this criterion, a hysteresis type of control policy was proposed. This policy consists of switching on control in case traffic density exceeds a critical value, and switching off control again as soon as traffic density becomes lower than another, smaller critical value. The hysteresis prevents switching the control on and off too often. The hysteresis policy was shown to be capable of postponing congestion considerably and increasing the flow slightly. The homogenization measure turns out to be the most effective for traffic intensity values lo%-15% below capacity. The policy is based on exact knowledge of the traffic state at each moment. This information is not available, but the filter developed in Chapter 5 of this dissertation may be used to obtain an estimate of the state. This algorithm estimates the state of traffic, consisting of traffic densities and mean speeds of all freeway sections, from the available count and speed measurement data.
Cost-effective decisions and life-cycle cost in diamond interchange design. Oh, Young Tae, Ph.D. Polytechnic University, 1989. 194 pp. Advisor: William R. McShane Order Number DA89101 15 The conventional diamond interchange design is commonly used because of its low cost and design simplicity. However, as development takes place and traffic volumes increase, a revised design is often needed; but the amount of space which can be devoted to the additional right-of-way is often limited due to financial and social reasons, and preexisting devel-
opment in the vicinity. Therefore, it is necessary to consider other types of interchange designs (such as split diamond interchanges) at the time of initial construction. If the traffic demand levels and patterns were static, the selection of a configuration would be straightforward. However, demand is not static; therefore, the “life cycle” approach is used. Life cycle costing is a methodology that evaluates the relative advantages of various interchange designs by considering the total present value of an interchange over its life cycle, considering all identifiable cost elements. The cost elements considered herein are capital cost, maintenance and operation cost, vehicle operating cost, and accident cost. In order to support the life cycle cost approach in this application, extensive simulation work was required. It has been found that the traffic pattern determines the nature of an interchange. Traffic patterns with high left-turn movements especially impact the capacity of the conventional diamond interchange. A set of equations for signal coordination was developed for the various traffic patterns in the split diamond interchange. As a result of the simulation work and the life cycle cost model, it was found that the conventional diamond is more sensitive to traffic pattern changes and the volume growth than a split diamond. The conventional diamond generally has less initial capital cost. However, the split diamond generally has less total cost over the life cycle and provides more capacity. While the stacked diamond handles highly directional flows, it is an extremely expensive design in capital cost. A series of case study “widening retrofit” and “build it once” cases are considered; the former generally has less capital cost and more cost.in total present value than the latter.
The design and performance of signal-controlled intersections. Hounsell, N. B., Ph.D. University of Southampton 360 pp.
(United Kingdom),
1989.
Order Number BRDX88094 This thesis describes research undertaken into the design and performance of signal-controlled intersections in the U.K., with particular emphasis on the measurement and prediction of junction capacity. The research is based largely on analysis of data collected at over 70 signal-controlled junctions throughout the country and on simulation modelling to investigate specific detailed aspects of traffic performance. The data collection techniques employed also allowed alternative data measurement and parameter calculation procedures which are commonly used elsewhere to be evaluated and biases inherent in certain procedures to be identified and quantified. Models for predicting saturation flow, a key determinant of capacity, are developed to cover individual
Analysis of traffic spatial shift resulting from optimal signal timing and special generators. Dikun, Suyono, Ph.D. The University of Wisconsin-Mu&son, 1988. 241 pp. Supervisor: Robert L. Smith, Jr. Order Number DA8903274 Traffic spatial shift as a result of traffic signal optimization in an urban corridor was investigated based on both the existing condition and potential future conditions with higher travel demand. The impacts of this spatial shift on the optimal signal timing, and vice versa, was analyzed through an iterative application of a traffic signal optimization model and a traffic diversion model. TRANSYT7F was used to optimize the signal system in the corridor network and to estimate overall traffic performance, including route travel times. A simple traffic diversion model developed from a logit choice model was chosen to represent the aggregate response of travelers to the choice situation. An algorithm for the interaction of TRANSYT7F and the diversion model was developed so that traffic equilibrium can be reached quickly. The initial optimization of signal timing created differences in travel time on alternative routes of 5 %6%. The iterative application of the traffic diversion model followed by simulation of the new flow conditions with TRANSYT-7F resulted in changes in link flow levels of l %-3 %. The new traffic flow conditions at equilibrium, however, did not significantly
45
affect the overall network measures of effectiveness (MOEs). Subsequent reoptimization of the signal timing based on the new link flow levels followed by traffic diversion to reach equilibrium resulted in only a 1% reduction in the performance index (PI) after the third optimization. Incremental expansion of the base outbound flows by 10X-30% was used to model the potential impacts of special generators on signal timing and spatial shift. In contrast to the base flow simulation, the performance of the network with the higher flows declined (higher PI) by 2%-8% in reaching equilibrium. Subsequent reoptimization resulted in improvements in the PI at equilibrium of up to 5 % . For the highly limited range of network, traffic signal, and flow conditions examined in this research, a reoptimization may be warranted if the travel time differences exceed 15 % in both directions.
Computerization of heuristic-based decisionmaking problems in transportation engineering. Faghri, Ardeshir, Ph.D. University of Virginia, 1989. 292 pp. Order Number DA9002842 This study investigates the potential applications of knowledge-based expert systems in transportation engineering. The three major topics covered are: (i) A description of the fundamental concepts of knowledge-based expert systems and how they relate to transportation engineering. The general differences between expert systems and conventional computer programs are summarized, and the process of transferring knowledge from human experts to computers is described. The architecture of knowledge-based expert systems is shown to separate the knowledge of the problem domain (knowledge base) from general problem solving (inference engine). Different approaches to each of these tasks are described and recent applications to several transportation engineering problems are presented. (ii) The selection of appropriate representation techniques for different classes of transportation engineering problems. Three of the most commonly used techniques for representing knowledge in the knowledge base of knowledge-based expert systems are described; and the highlights, shortcomings, and applications of each technique are explained. This section focuses on an examination of the significance of the means of representing the knowledge base in the development of knowledge-based expert systems, with special reference to five classes of transportation engineering problems-planning, operations and control, design, construction and maintenance, and management and finance. Under each class, one or two transportation and traffic problems suitable for knowledge-based expert systems development are briefly described, and the most suitable representation technique(s) for their development is recommended. (iii) A descrip-
Book Reviews
46
tion of the development of one transportation engineering problem chosen from the previous section. The stages required in the development of a knowledge-based expert system -problem identification, conceptual analysis, formalization, implementation, and evaluation- for the chosen problem are described in detail.
Control of freeway traffic flow. Smulders, Stef A., Dr.ing. University 1989. 162 pp.
of i%ente
(Netherlands),
In this thesis, a freeway traffic control problem has been addressed and solved. The control problem consists of designing an optimal policy for the variable speed signs of the Dutch Motorway Control and Signalling System. The aim is to reduce the instabilities of traffic flow that occur if demand is high, and thereby to reduce the probability of congestion and increase safety. For the design of an optimal control policy, we proposed a criterion which measures the expected total throughput of a freeway section until the moment of congestion. Based upon the policies obtained with this criterion, a hysteresis type of control policy was proposed. This policy consists of switching on control in case traffic density exceeds a critical value, and switching off control again as soon as traffic density becomes lower than another, smaller critical value. The hysteresis prevents switching the control on and off too often. The hysteresis policy was shown to be capable of postponing congestion considerably and increasing the flow slightly. The homogenization measure turns out to be the most effective for traffic intensity values lo%-15% below capacity. The policy is based on exact knowledge of the traffic state at each moment. This information is not available, but the filter developed in Chapter 5 of this dissertation may be used to obtain an estimate of the state. This algorithm estimates the state of traffic, consisting of traffic densities and mean speeds of all freeway sections, from the available count and speed measurement data.
Cost-effective decisions and life-cycle cost in diamond interchange design. Oh, Young Tae, Ph.D. Polytechnic University, 1989. 194 pp. Advisor: William R. McShane Order Number DA89101 15 The conventional diamond interchange design is commonly used because of its low cost and design simplicity. However, as development takes place and traffic volumes increase, a revised design is often needed; but the amount of space which can be devoted to the additional right-of-way is often limited due to financial and social reasons, and preexisting devel-
opment in the vicinity. Therefore, it is necessary to consider other types of interchange designs (such as split diamond interchanges) at the time of initial construction. If the traffic demand levels and patterns were static, the selection of a configuration would be straightforward. However, demand is not static; therefore, the “life cycle” approach is used. Life cycle costing is a methodology that evaluates the relative advantages of various interchange designs by considering the total present value of an interchange over its life cycle, considering all identifiable cost elements. The cost elements considered herein are capital cost, maintenance and operation cost, vehicle operating cost, and accident cost. In order to support the life cycle cost approach in this application, extensive simulation work was required. It has been found that the traffic pattern determines the nature of an interchange. Traffic patterns with high left-turn movements especially impact the capacity of the conventional diamond interchange. A set of equations for signal coordination was developed for the various traffic patterns in the split diamond interchange. As a result of the simulation work and the life cycle cost model, it was found that the conventional diamond is more sensitive to traffic pattern changes and the volume growth than a split diamond. The conventional diamond generally has less initial capital cost. However, the split diamond generally has less total cost over the life cycle and provides more capacity. While the stacked diamond handles highly directional flows, it is an extremely expensive design in capital cost. A series of case study “widening retrofit” and “build it once” cases are considered; the former generally has less capital cost and more cost.in total present value than the latter.
The design and performance of signal-controlled intersections. Hounsell, N. B., Ph.D. University of Southampton 360 pp.
(United Kingdom),
1989.
Order Number BRDX88094 This thesis describes research undertaken into the design and performance of signal-controlled intersections in the U.K., with particular emphasis on the measurement and prediction of junction capacity. The research is based largely on analysis of data collected at over 70 signal-controlled junctions throughout the country and on simulation modelling to investigate specific detailed aspects of traffic performance. The data collection techniques employed also allowed alternative data measurement and parameter calculation procedures which are commonly used elsewhere to be evaluated and biases inherent in certain procedures to be identified and quantified. Models for predicting saturation flow, a key determinant of capacity, are developed to cover individual