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871.
872.
After nearly a half century of federal and state regulation, the U.S. intercity bus industry is the subject of proposals which would drastically reduce the extent of governmental control over fare setting, service abandonment, and market entry. An essential requirement for understanding how these regulatory changes might affect the industry is knowing the extent to which economies of scale are present in the provision of intercity bus services. This paper reports on the analysis of economies of scale for both Class I firms and for Class II and III firms. The results show nearly constant returns to scale beyond very low output levels but very strong dependence on the mix of charter and regular-route service provided. 相似文献
873.
D. R. Glen 《Maritime Policy and Management》1996,23(2):201-207
Thie paper re-examines the link between shipping investment and investment incentives, first explored in this journal by Marlow, and subsequently developed by mcWilliams et al. in the July-September issue. Examination of the ststistical properties of the data reveals that some of McWilliams' results may be flawed. A modified version of the Marlow model is estimated. checking for statistical and economic consistency, using cointegration, checking for statistical and economic consistency, using cointegration techniques. The estimated model resolves marlow's original challenge, but does not appear to be as robust as could be wished. 相似文献
874.
Hyuk Kim Graduate student Yong-San Yoon Professor Ph.D 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1995,24(10):759-780
The objective of this study is to develop a control law for a semi-active suspension for the purpose of ride quality improvement. The semi-active control law is determined by reproducing the control force of an optimally controlled active suspension while suppressing its damping coefficient variation. The performance index of the optimal control for the active suspension is modified to include frequency-shaping by use of Parseval's theorem, which allows us to de-emphasize the effects of particular variables over specific frequency bands.
Through the numerical simulations, it was found that the semi-active suspension may reduce the vertical acceleration of the driver's seat and the sprung mass motions significantly. The road-holding and tire deflections were not affected much. 相似文献
Through the numerical simulations, it was found that the semi-active suspension may reduce the vertical acceleration of the driver's seat and the sprung mass motions significantly. The road-holding and tire deflections were not affected much. 相似文献
875.
This paper provides a framework for assessing the progress that is being made in the computer-assisted dispatching of trains. The state of the art is described in general terms, and future research needs are identified. 相似文献
876.
Accessibility measures reflect the level of service provided by transportation systems to various locations. Basic transportation choice behavior is defined to include those decisions of how many automobiles to own and how many trips to which destinations to make by automobile and by public transit. Here, these decisions are assumed to be made jointly by urban households and are conditional upon residential location decisions. It is the purpose of this paper to explore the role of accessibility as a causal factor in such basic transportation choice behavior.An economic utility theory model of choice behavior is postulated in which the benefits from making trips to specific destinations are reflected by measures of destination attraction. Through determination of utility-maximizing trip frequencies, indirect utility functions are developed which include accessibility concepts. Behavioral implications of these concepts are proposed and contrasts are drawn to accessibility measures used in conventional segregated models of trip distribution, modal choice, and automobile ownership.Sensitivity analyses of alternative empirical definitions of accessibility in the choice model are conducted using data from the Detroit Regional Transportation and Land Use Study — covering counties in southeastern Michigan. These analyses employ a multinomial logit estimation technique and focus on definitions of trip attraction. Results of these analyses indicate that more complicated attraction measures can be replaced by measures involving the proportion of either urban area population or urban area employment within a traffic analysis zone. Also, evidence is found that decision-makers in the case study area consider trips of up to 60 or even 90 minutes duration when evaluating accessibilities offered by alternative public and private transportation systems. 相似文献
877.
878.
This paper looks at the relationships between ship size, handling rate and ship berth time for five major ports in the United Kingdom. The results show that there is no simple linear relationship between these variables. The causes and implications of this are discussed. 相似文献
879.
R. C. Redfield D. C. Karnopp 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1988,17(5):231-253
Most vehicle suspension systems use fixed passive components that offer a compromise in performance between sprung mass isolation, suspension travel, and tireroad contact force. Recently, systems with discretely adjustable dampers and air springs been added to production vehicles. Active and semi-active damping concepts for vehicle suspensions have also been studied theoretically and with physical prototypes. This paper examines the optimal performance comparisons of variable component suspensions, including active damping and full-state feedback, for “quartercar” heave models. Two and three dimensional optimizations are computed using performance indicators to find the component parameters (control gains) that provide “optimal” performance for statistically described roadway inputs. The effects of performance weighting and feedback configuration are examined. Active damping is shown to be mainly important for vehicle isolation. A passive vehicle suspension can control suspension travel and tire contact force nearly as well as a full state feedback control strategy. 相似文献
880.
介绍「台湾桃园国际机场联外捷运系统建设计划」中机场区段地下工程的设计成果,并探讨施工时将面临的主要工程问题如,潜盾隧道穿越营运中的机场滑行道下方需考虑对其进行保护、隧道遭遇既有地锚的处理方式,及明挖覆盖隧道或车站于卵砾石层进行开挖,临时挡土措施及潜盾隧道的掘进作业,需考虑卵砾石大粒径与高硬度的特性等等设计考虑.现有数据显示,透过适当的机具改良、辅助工法的应用及良好的施工管理,即使是在高地下水压的卵砾石层,施作地下连续壁及以潜盾机施作隧道并无太大困难,且施工引致的地表沉陷及施工精度亦可获得良好的控制. 相似文献