Analytic optimization of bus systems in heterogeneous environments
出版項
1990
說明
1 online resource (172 pages)
文字
text
無媒介
computer
成冊
online resource
附註
Source: Dissertations Abstracts International, Volume: 52-04, Section: B
Publisher info.: Dissertation/Thesis
Advisor: Schonfeld, Paul M
Thesis (Ph.D.)--University of Maryland, College Park, 1990
Includes bibliographical references
Analytic models for optimizing transportation systems have typically sacrificed geographic details and temporal variations in demand and supply parameters in order to identify optimal relations among certain decision variables and parameters in closed form. The applicability of such models has been limited by their simplifying assumptions about idealized environments. In this work, analytic optimization models are developed for bus systems with temporal and/or spatial heterogeneity in their supply and demand characteristics. Such characteristics are specified directly with general empirical distributions rather than smoothed functions. These models allow the optimal values of some design variables to vary over space (e.g., stop spacing) and/or time (e.g., service headway) while determining unique values for other design variables (e.g., route spacing) which represent the optimal compromise over the relevant set of space and time elements. Several bus systems with different supply characteristics and demand patterns are analyzed. These include feeder systems (both fixed and flexible route) with many-to-one demand patterns and parallel route systems with many-to-many demand patterns. Mathematical optimization models are developed for various objectives, including total cost minimization for inelastic demand cases as well as profit or social welfare maximization for elastic demand cases. For such objectives, closed form solutions are derived and compared for the optimal design variables (such as route spacing, headway, optimal route or tour length, vehicle size and fare), the system costs, and the objective functions themselves. Analytic solutions are shown to be globally optimal even with subsidy or profitability constraints. Interrelations among the optimized decision variables and the system parameters are identified for various cases. These analytic results show more clearly than any numerical results what the relations among variables should be for optimized bus systems. Optimality conditions are found which may lead to improved system evaluation and numerical optimization methods. These include the equality of wait costs, access costs, operator costs, and revenues under specified conditions. Threshold analyses examine at what demand densities flexible route paratransit services are preferable to conventional fixed route services. Temporally integrated systems providing fixed route services during higher demand periods and flexible route services during lower demand periods are found to have lower average trip costs than either pure system. Many-to-many demand patterns that may be directionally imbalanced during various periods and include combinations of concentrated and linearly distributed trip generators are analyzed with parallel route models. The applicability of analytic models is thus extended to fairly complex environments and transportation systems
Electronic reproduction. Ann Arbor, Mich. : ProQuest, 2020
