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A study of alternative approaches to combined trip distribution-assignment modeling
Bibliographic Section
291
DISSERTATION ABSTRACTS
The Economics of Airport Planning: The Case of Toronto, Sandford F. Borins, Department of Policy and Environment, Graduate School of Management, Northwestern University, Evanston, IL 60201. (Dissertation in the Department of Economics, Harvard University, Cambridge, MA 02138). There are two literatures on airport planning: the detailed simulation models of engineers and planners, which ignore the allocative use of prices, and the optimal pricing and investment models of economists, which fail to capture the physical complexity of airports. The thesis attempts to combine the best of both approaches. The thesis deals with Toronto because the proposal by the Canadian Ministry of Transport to build a second international airport for Toronto has aroused controversy, which has brought to light substantial planning data. The thesis reviews the Ministry of Transport's forecasts of air passenger demand for Toronto. They were based on a propensity model which employed 1971 survey data of Toronto-based passengers to generate per-capita trip-making coefficients for population groups and multiplied these coefficients b y forecasts of the sizes of the population groups. The model was criticized for several reasons: sampling errors; errors in applying sample data; the excessive use of judgment rather than measurement, the use of a questionable calibration factor, and the omission of prices in modifying trip-making coefficients; the application of cross-sectional trip-making coefficients to behavior over time; and the unwarranted assumption that trips to Toronto by passengers based elsewhere will grow at the same rate as trips of Toronto-based passengers. The forecasts were re-estimated and demand was predicted to grow at a slower rate. A network simulation model was built to determine optimal pricing and investment in Toronto airports. The model determined equilibrium flows through the congested facilities (runways, terminals, access roads) throughout a typical day. The model is solved as a system of N by T simultaneous non-linear equations in N by T unknowns, where N is the number of congested facilities and T the number of periods in the day. This was done using MARQRDT, a computer routine for solving systems of equations by means of a steepest-descent search. Operations of the existing airport in 1975 and 1980 were simulated: it was found that social welfare, defined as net economic surplus, would be increased relative to the status quo if marginal cost pricing were instituted at all facilities. Demand forecasts into the 1980's were used to determine optimal opening dates for additional facilities; the alternative locations considered were on-site expansion of the existing airport and construction of a new airport.
Some results were: expansion of facilities is required sooner if present airport pricing policies are used than if there is marginal cost pricing; optimal opening dates at either location, based on the economic surplus criterion, occur about five years later than those recommended by the Ministry of Transport, based on engineering criteria; and capacity should be added first at the existing airport rather than at a new site. A sensitivity analysis found that slower demand growth delayed all optimal opening dates but did not affect the preference for the existing airport and that more optimistic assumptions about future aircraft noise reduction technology increased the preference for the existing airport. The thesis explains the difference between the policies of the Ministry of Transport and those suggested by economic analysis. The Ministry of Transport is a client-oriented risk-averse organization. Marginal cost pricing conflicts with client orientation. Risk aversion dictates construction ahead of demand because the risk of displeasing the passenger is viewed as more serious than that of too-hasty spending of tax dollars. It is suggested that changes in the external environment, such as citizen opposition to new airports and central policy-makers according a lower priority to transportation project now than previously, may force the Ministry of Transport to change its policies to increase economic efficiency.
A Study of Alternative Approaches to Combined Trip Distribution-Assignment Modeling, Carolyn Frank, System Design Concepts, Inc., One Farragut Square South, Washington, DC 20006 (dissertation in the Department of Regional Science, University of Pennsylvania, Philadelphia, PA 19104).
The research problem is to analyze equilibrium-type combined trip distribution-assignment models. Combined models integrate two of the standard aggregate sequential transportation demand models, trip distribution and trip assignment. Equilibrium transportation models converge to a set of results which remain stable unless altered by an outside stimulus. Evans has derived the combined trip distributionassignment model and suggested an algorithm for its solution. Florian, Nguyen and Ferland have proposed an alternative derivation a n d algorithm. Although they differ in terms of derivation and solution technique, the two models share the same mathematical programming formulation.
292
Bibliographic Section
In order to study the properties of the combined model when confronted by a realistic planning problem, the two alternative algorithms were coded as computer algorithms. Questions about the properties associated with convergence and the limitations of the models were posed. Properties associated with convergence include the existence, speed and path to the equilibrium. Limitations of these models are studied by exploring the costs of using the models, and by analyzing the sensitivity of the results to changes in the input data and parameters. The method employed is to perform a set of computer experiments with each model. Both computer algorithms are applied to the same network for comparative purposes. Differences in the performances of the computer algorithms will thus only be caused by the underlying divergent solution techniques. The basic network and travel data are for a small region in Canada, the area in and around the city of Hull. This data set was selected because it is larger than typical constructed data sets and thus includes more natural complexity. Available computer funds did not permit consideration of larger networks. In order to investigate each research question, the input data or parameters were adjusted to reflect the hypothesis. Both iterative computer algorithms were applied to this data and the resulting trip tables and flows on the links of the network were analyzed. Each computer algorithm demonstrated convergent behavior; however, they did not converge to the same result. According to the gradient criteria, neither computer algorithm reached the equilibrium result. Each algorithm found a better solution during each iteration; this is a portrayal of convergent behavior. The Evans algorithm rapidly terminated, possibly due to the build up of rounding errors, shy of the equilibrium. The Florian et al. algorithm took twice as long to reach a local optimum much further away from the equilibrium. The predicted trip tables and flows on the links produced by the two computer algorithms are markedly different. Although the two algorithms have analogous structures, the different methods of predicting trip tables cause divergent paths to be taken towards the equilibrium. Both computer algorithms have successfully dealt with low and high levels of congestion. Because combined models utilize travel costs along the links which increase with increased flow, they are ideally suited to be used in situation with congested conditions. Both computer algorithms are sensitive to the value specified for the parameter of the negative exponential deterrence function. The computer algorithms are not very sensitive to modifications in the values of termination criteria required for some of the embedded routines. In comparison to the Florian et al. algorithm, the Evans algorithm approaches the equilibrium more rapidly and closer. The Evans algorithm is shown to be competitive in terms of cost with the separate trip
distribution and assignment models currently used. As a direct substitute for these two models, the combined model would provide complementary predictions of interzonal trips and link flows, while taking the underlying level of congestion into account throughout the entire modeling process.
Airports and Human Values: An Attempt to Increase the Weight of Ethical Considerations as Design Criteria, Elisha Novak (dissertation in the Department of
Architecture, University of California, Berkeley, CA 94720).
The activities of planning and design are supported by a variety of skills and tools, one of which is design criteria. These include standards, rules, laws, and commonly accepted notions. It is suggested by this dissertation, however, that ethical concerns do not receive proper treatment as compared with other design criteria. This treatise, therefore, draws heavily on a variety of fields, including philosophy, psychology, economics, sociology, architecture, management science, systems science, planning, health, and transportation engineering, in an attempt to give ethical concerns a more balanced consideration as a design criteria. The engineering and architectural approaches to design are described, and it is suggested that each type of professional emphasizes a single criterion (engineers---efficiency, architects--form) to the neglect of other relevant issues. It is concluded, therefore, that ethical concerns are not given a balanced consideration as a design criterion by these two design approaches. A more balanced consideration of ethical concerns is possible, according to this treatise, through the application of a humanistic design process, which obtains information about how people's values may be better accommodated. This task is accomplished through the identification and protection of fundamental human requirements as revealed by the primary values people hold. Information about primary values should be gathered from philosophical and religious writings on ethics, through unobtrusive observations of behavioral traits, and from other sources, when relevant. These are then to be converted into design criteria and implemented through an ethically appropriate institutional decision-making process. A discussion of the concept of human values reveals some ambiguities in the meaning of the term, its measurement, stability, and the application of knowledge about it. The thesis adopts the meaning of value
291
DISSERTATION ABSTRACTS
The Economics of Airport Planning: The Case of Toronto, Sandford F. Borins, Department of Policy and Environment, Graduate School of Management, Northwestern University, Evanston, IL 60201. (Dissertation in the Department of Economics, Harvard University, Cambridge, MA 02138). There are two literatures on airport planning: the detailed simulation models of engineers and planners, which ignore the allocative use of prices, and the optimal pricing and investment models of economists, which fail to capture the physical complexity of airports. The thesis attempts to combine the best of both approaches. The thesis deals with Toronto because the proposal by the Canadian Ministry of Transport to build a second international airport for Toronto has aroused controversy, which has brought to light substantial planning data. The thesis reviews the Ministry of Transport's forecasts of air passenger demand for Toronto. They were based on a propensity model which employed 1971 survey data of Toronto-based passengers to generate per-capita trip-making coefficients for population groups and multiplied these coefficients b y forecasts of the sizes of the population groups. The model was criticized for several reasons: sampling errors; errors in applying sample data; the excessive use of judgment rather than measurement, the use of a questionable calibration factor, and the omission of prices in modifying trip-making coefficients; the application of cross-sectional trip-making coefficients to behavior over time; and the unwarranted assumption that trips to Toronto by passengers based elsewhere will grow at the same rate as trips of Toronto-based passengers. The forecasts were re-estimated and demand was predicted to grow at a slower rate. A network simulation model was built to determine optimal pricing and investment in Toronto airports. The model determined equilibrium flows through the congested facilities (runways, terminals, access roads) throughout a typical day. The model is solved as a system of N by T simultaneous non-linear equations in N by T unknowns, where N is the number of congested facilities and T the number of periods in the day. This was done using MARQRDT, a computer routine for solving systems of equations by means of a steepest-descent search. Operations of the existing airport in 1975 and 1980 were simulated: it was found that social welfare, defined as net economic surplus, would be increased relative to the status quo if marginal cost pricing were instituted at all facilities. Demand forecasts into the 1980's were used to determine optimal opening dates for additional facilities; the alternative locations considered were on-site expansion of the existing airport and construction of a new airport.
Some results were: expansion of facilities is required sooner if present airport pricing policies are used than if there is marginal cost pricing; optimal opening dates at either location, based on the economic surplus criterion, occur about five years later than those recommended by the Ministry of Transport, based on engineering criteria; and capacity should be added first at the existing airport rather than at a new site. A sensitivity analysis found that slower demand growth delayed all optimal opening dates but did not affect the preference for the existing airport and that more optimistic assumptions about future aircraft noise reduction technology increased the preference for the existing airport. The thesis explains the difference between the policies of the Ministry of Transport and those suggested by economic analysis. The Ministry of Transport is a client-oriented risk-averse organization. Marginal cost pricing conflicts with client orientation. Risk aversion dictates construction ahead of demand because the risk of displeasing the passenger is viewed as more serious than that of too-hasty spending of tax dollars. It is suggested that changes in the external environment, such as citizen opposition to new airports and central policy-makers according a lower priority to transportation project now than previously, may force the Ministry of Transport to change its policies to increase economic efficiency.
A Study of Alternative Approaches to Combined Trip Distribution-Assignment Modeling, Carolyn Frank, System Design Concepts, Inc., One Farragut Square South, Washington, DC 20006 (dissertation in the Department of Regional Science, University of Pennsylvania, Philadelphia, PA 19104).
The research problem is to analyze equilibrium-type combined trip distribution-assignment models. Combined models integrate two of the standard aggregate sequential transportation demand models, trip distribution and trip assignment. Equilibrium transportation models converge to a set of results which remain stable unless altered by an outside stimulus. Evans has derived the combined trip distributionassignment model and suggested an algorithm for its solution. Florian, Nguyen and Ferland have proposed an alternative derivation a n d algorithm. Although they differ in terms of derivation and solution technique, the two models share the same mathematical programming formulation.
292
Bibliographic Section
In order to study the properties of the combined model when confronted by a realistic planning problem, the two alternative algorithms were coded as computer algorithms. Questions about the properties associated with convergence and the limitations of the models were posed. Properties associated with convergence include the existence, speed and path to the equilibrium. Limitations of these models are studied by exploring the costs of using the models, and by analyzing the sensitivity of the results to changes in the input data and parameters. The method employed is to perform a set of computer experiments with each model. Both computer algorithms are applied to the same network for comparative purposes. Differences in the performances of the computer algorithms will thus only be caused by the underlying divergent solution techniques. The basic network and travel data are for a small region in Canada, the area in and around the city of Hull. This data set was selected because it is larger than typical constructed data sets and thus includes more natural complexity. Available computer funds did not permit consideration of larger networks. In order to investigate each research question, the input data or parameters were adjusted to reflect the hypothesis. Both iterative computer algorithms were applied to this data and the resulting trip tables and flows on the links of the network were analyzed. Each computer algorithm demonstrated convergent behavior; however, they did not converge to the same result. According to the gradient criteria, neither computer algorithm reached the equilibrium result. Each algorithm found a better solution during each iteration; this is a portrayal of convergent behavior. The Evans algorithm rapidly terminated, possibly due to the build up of rounding errors, shy of the equilibrium. The Florian et al. algorithm took twice as long to reach a local optimum much further away from the equilibrium. The predicted trip tables and flows on the links produced by the two computer algorithms are markedly different. Although the two algorithms have analogous structures, the different methods of predicting trip tables cause divergent paths to be taken towards the equilibrium. Both computer algorithms have successfully dealt with low and high levels of congestion. Because combined models utilize travel costs along the links which increase with increased flow, they are ideally suited to be used in situation with congested conditions. Both computer algorithms are sensitive to the value specified for the parameter of the negative exponential deterrence function. The computer algorithms are not very sensitive to modifications in the values of termination criteria required for some of the embedded routines. In comparison to the Florian et al. algorithm, the Evans algorithm approaches the equilibrium more rapidly and closer. The Evans algorithm is shown to be competitive in terms of cost with the separate trip
distribution and assignment models currently used. As a direct substitute for these two models, the combined model would provide complementary predictions of interzonal trips and link flows, while taking the underlying level of congestion into account throughout the entire modeling process.
Airports and Human Values: An Attempt to Increase the Weight of Ethical Considerations as Design Criteria, Elisha Novak (dissertation in the Department of
Architecture, University of California, Berkeley, CA 94720).
The activities of planning and design are supported by a variety of skills and tools, one of which is design criteria. These include standards, rules, laws, and commonly accepted notions. It is suggested by this dissertation, however, that ethical concerns do not receive proper treatment as compared with other design criteria. This treatise, therefore, draws heavily on a variety of fields, including philosophy, psychology, economics, sociology, architecture, management science, systems science, planning, health, and transportation engineering, in an attempt to give ethical concerns a more balanced consideration as a design criteria. The engineering and architectural approaches to design are described, and it is suggested that each type of professional emphasizes a single criterion (engineers---efficiency, architects--form) to the neglect of other relevant issues. It is concluded, therefore, that ethical concerns are not given a balanced consideration as a design criterion by these two design approaches. A more balanced consideration of ethical concerns is possible, according to this treatise, through the application of a humanistic design process, which obtains information about how people's values may be better accommodated. This task is accomplished through the identification and protection of fundamental human requirements as revealed by the primary values people hold. Information about primary values should be gathered from philosophical and religious writings on ethics, through unobtrusive observations of behavioral traits, and from other sources, when relevant. These are then to be converted into design criteria and implemented through an ethically appropriate institutional decision-making process. A discussion of the concept of human values reveals some ambiguities in the meaning of the term, its measurement, stability, and the application of knowledge about it. The thesis adopts the meaning of value