Ship assignment with hub and spoke constraints

As the shipping industry enters the future, an increasing number of technological developments are being introduced into this market. This has led to a significant change in business operations, such as the innovative design of hub and spoke systems, resulting in cargo consolidation and a better use of the ship's capacity. In the light of this new scenario, the authors present a successful application of integer linear programming to support the decision-making process of assigning ships to previously defined voyages - the rosters. The tool used to build the final models was the MS-Excel Solver (Microsoft® Excel 97 SR-2, 1997), a package that enabled the real case studies addressed to be solved. The results of the experiment prompted the authors to favour the assignment of very small fleets, as opposed to the existing high number of ships employed in such real trades,     

Numerical experiments on the prediction of sea surface temperature anomalies in the Gulf of Mexico

The conservation of thermal energy equation applied to the mixed layer of the ocean, has been used to predict the sea surface temperature anomalies (SSTA) and the month-to-month changes in the Gulf of Mexico. The model includes the horizontal transport of heat by mean ocean currents and by turbulent eddies, as well as the heating by short and long wave radiation, evaporation and sensible heat given off to the atmosphere. A comparative study is carried out on the relative importance of the heating and transport terms. An objective verification of the skill of the predictions is presented for each season and for the whole period from March 1986 to February 1987. The predictions using only the heating terms have some skill over the control predictions (persistence and return to normal). The skill is substantially increased when the horizontal transport of heat by turbulent mixing is included in the model. The incorporation in the model of the Ekman wind drift current anomalies computed from the anomalous surface geostrophic wind improves appreciably the skill of the predictions in winter and fall.The mixed layer depth computed using the Kraus and Turner theory with dissipation, shows that the depths in summer and fall are shallower than in spring and winter. The effect of the shallow mixed layer depth in the model becomes apparent in summer and fall, improving the skill of the predictions in these seasons, with respect to the skill obtained using a constant mixed layer depth of 60 m.The incorporation in the model of the cooling in the mixed layer by turbulent entrainment of colder water from the thermocline, does not improve in an appreciable way the average skill of the predictions.     

Effects of subsidies on urban public transport

Because of a general trend of increasing costs of public transport operations and higher subsidies (in some cases accompanied by falling patronage) the European Conference of Ministers of Transport (ECMT) initiated a study of subsidisation and sought the help of the Transport and Road Research Laboratory. The study, in which eighteen countries took part, was concerned with the aims of subsidy, the sources and conditions attached to subsidy, trends in subsidies and the effect of subsidies on patronage, fares, service levels, costs and productivity.The qualitative information concerning the aims of subsidy was analysed in relation to the likelihood of achieving such aims, taking into account current experience of attempts to switch car drivers to public transport. The quantitative information on trends referred to public transport stage services covering where possible the entire country and relating to the period 1965–77; these data were supplemented by data from 59 cities in different parts of the world collected in the course of a TRRL-sponsored study of travel demand factors. The relationship between patronage and service levels, and between subsidies and various operating factors, including costs and productivity, were studied using regression analysis and the general conclusion reached was that although the major part of the subsidy paid was reflected by reduced fares and improved service levels there may well have been some leakage into higher unit costs and manning levels.     

The relationship between transportation perceptions and behavior over time

The aim of this paper is to discuss cross-lagged panel analysis in terms of the causal inferences it generates about the relationship of beliefs about modes and mode choice behavior. Frequencies of use of the single-occupant automobile (SOA), bus and carpool, as well as beliefs about each of the modes, were collected from a sample of central business district commuters at two points in time. The belief variables for each mode were summed to form composite measures and were corrected for unreliability due to measurement error.Perceptions of each mode and the frequency of its use were analyzed for influences operating over time. A time interval was assumed to exist during which the variables causally operated on each other. It was assumed that the time necessary for an individual to change modes based on his perception was equivalent to the interval required for a person to alter perceptions based on his experience. The causal structure relating the two variables was also assumed to be stable over time. An additional assumption was required to distinguish between third variable effects, or spuriousness, and dual causation: if a third variable were to be causing the relationship, it would be operating at a relatively constant rate over time.A strong causal relationship was found to be operating between beliefs about SOA and bus and use of those modes over time. The relationship is mutually causative; beliefs determine behavior and behavior reinforces and changes perceptions. Analysis of the carpool data indicated that the causal structure had changed over time and could not be analyzed with this technique. In general, support is evidenced for an adaptation or learning process interpretation of the relationship between beliefs and mode choice behavior.     

Planning for implementation

Although the urban transportation planning process has evolved into the most sophisticated of all urban planning processes, the increasirig difficulty in implementing long-range transportation plans in urban areas today suggests basic questions concerning the process which deserve critical examination.Planning for implementation of urban transportation programs, particularly during periods of rapidly changing human values, requires a continuing re-evaluation of both technical and organizational strategies and their interrelationships.This paper raises some fundamental questions about the traditional activities and relationships that have characterized most urban transportation planning programs in the past. It also suggests a number of strategies, both technical and organizational, that may contribute to the implementation of plans and programs resulting from the transportation planning process.The first portion of this paper discusses the implications of not providing transportation services to match metropolitan growth. The experience of the Washington Metropolitan Area over the past decade is used to illustrate these implications.A discussion of organizational and institutional constraints upon the planning process follows. Then, the implications for the planning process are explored, and the scale of planning is reviewed as well as the need for monitoring the performance and impact of facilities.Next, the paper deals with the need to broaden the range of solutions to transportation problems, including consideration of economic and land development policies to reduce travel demand, as well as the provision of new facilities.Finally, techniques for involving decision-makers in the planning process are discussed. Examples of special project activities in the Washington area are used to illustrate these techniques and their value.     

Speed management via in-car devices: effects,implications, perspectives

The objectives of this paper are to identify in-vehicle systems for speed management that have been or are being developed, and to suggest recommendations for the implementation of systems that will effectively influence driving speeds and thereby significantly increase safety. The best safety effect is expected from an "intelligent" gas pedal, more specifically the automatic speed limiter. However, in terms of user acceptance, this system is least liked, although, acceptance seems to improve after it has been tried out. Nonetheless, the final goal for implementation should be a mandatory speed limiter system, starting with voluntary usage supported with educational measures. A period of car producers' standardisation of ISA-systems should be followed by legislation prescribing that all new vehicles are to be fitted with the system. Finally, some questions regarding further research are outlined.     

Testing a Framework for the Efficiency Assessment of Road Safety Measures

Abstract

The objective of this research is to develop and test a framework for efficiency assessment of road safety measures and evaluate its use in decision‐making. An exhaustive review of standard methodologies and practices related to cost‐effectiveness and cost–benefit analyses is carried out for that purpose. Moreover, a number of case studies are performed, concerning the efficiency assessment of various road safety measures in different countries, covering different types of road safety measures (user‐, vehicle‐ or infrastructure‐oriented, policy or enforcement, etc.), ranging from national to local levels of implementation and including both ex ante and ex post evaluations. From the results conclusions are drawn on the efficiency of different road safety measures and the related determinants. Furthermore, the case studies reveal a number of methodology and data issues for which further research is required. The procedures and barriers involved in the use of efficiency assessment techniques at different levels of decision‐making are also highlighted by means of feedback received during and after the various case studies. On the basis of these results, a framework for the promotion, implementation and evaluation of efficiency assessment in road safety decision‐making is proposed. A particular set of recommendations is also presented regarding the treatment of barriers (fundamental, institutional or technical) within the efficiency assessment itself and the related decision‐making process.     

Why are maritime ports (still) urban,and why should policy-makers care?

Despite ongoing transformations in the maritime transportation industry and the rise of global supply chain systems, most of the world's important container ports remain urban. Ports continue to occupy urban spaces, are embedded in localized knowledge systems, draw on urban labour markets and infrastructure and are subject to local politics and policy concerns. We identify contemporary geographic theories which help us understand the often increasingly urban attachment of core economic activities despite globalization. We explore how these theories may apply to port studies, highlighting both how they have been used by maritime scholars to this point and also why further development and application are warranted. We argue that a central concern of these geographic theories is the articulation of place- and sector-specific processes operating at a variety of spatial scales. This is in contrast to most maritime studies which continue to be dominated by perspectives which emphasize the global logic of the transportation industry and the analysis of space in generalized and abstract terms. We conclude that a re-appreciation in maritime studies of urban economic processes, informed by geographical theory, will provide policy-makers and others with more understanding of why deep connections between ports and urban places still matter.     

双向与单向道路网络:哪一个更高效?

为了改善机动车的可达性并避免驾驶人迷失,城市政府和规划师开始将中心城区传统的单向道路网络转换成双向行驶。双向道路网络可提升经济活力水平和中心城区的宜居性,而单向道路网络可提高通行能力。指出使用出行服务能力指标来衡量道路网络效率更适宜,将单向行驶与双向行驶道路网络的出行服务能力进行对比,后者交叉口的处理包括左转专用车道、左转渠化和禁止左转三种方式。结果显示,与传统认知和设计手册相反,双向道路网络通常比单向道路网络更有效率。在出行距离较短的情况下,允许转向的双向道路网络比单向道路网络的出行服务能力更高;禁止左转的双向道路网络比单向道路网络造成的绕行更少。     

Simulation of longitudinal dynamics of a freight train operating through a car dumper

A heavy haul train and car dumper model was created to analyse train longitudinal dynamics during dumping. Influence of such factors as performance curve of draft gears, total free slack in couplers, operating mode of train positioner and braking of last two cars of train on the in-train forces was considered.