DDA方法中节理参数定义方式的改进

为提高非连续变形分析（discontinuous deformation analysis,DDA）方法程序中节理参数赋值的精度,在DDA原程序节理参数定义的基础上,提出了一种节理参数定义方式的改进方法.首先,根据节理的物理力学性质,对原DDA中节理参数定义存在的非一致性问题进行了分析;其次,由节理参数是由构成节理的两个结构面共同决定的特性,对程序中的节理参数进行了重新定义;最后,对DDA原程序中节理参数赋值部分进行了修改和补充,给出了相应的程序计算流程,并通过块体1和块体2的相对滑动算例对改进后的DDA程序进行了验证.研究结果表明:当块体1和块体2交换力学参数时,其间节理仍为同一性质节理;两种工况下,块体1的速度和位移保持一致,说明改进后的DDA程序能够很好地实现同一节理参数赋值的统一.      

The implications on willingness to pay of respondents ignoring specific attributes

Individuals processing the information in a stated choice experiment are typically assumed to evaluate each and every attribute offered within and between alternatives, and to choose their most preferred alternative. However, it has always been thought that some attributes are ignored in this process for many reasons, including a coping strategy to handle ones perception of the complexity of the choice task. Nonetheless, analysts typically proceed to estimate discrete choice models as if all attributes have influenced the outcome to some degree. The cognitive processes used to evaluate trade-offs are complex with boundaries often placed on the task to assist the respondent. These boundaries can include prioritising attributes and ignoring specific attributes. In this paper we investigate the implications of bounding the information processing task by attribute elimination through ignoring one or more attributes. Using a sample of car commuters in Sydney we estimate mixed logit models that assume all attributes are candidate contributors, and models that assume certain attributes are ignored, the latter based on supplementary information provided by respondents. We compare the value of travel time savings under the alternative attribute processing regimes. Assuming that all attributes are not ignored and duly processed, leads to estimates of parameters which produce significantly different willingness to pay (WTP) to that obtained when the exclusion rule is invoked.     

Modeling household activity–travel interactions as parallel constrained choices

The daily activity-travel patterns of individuals often include interactions with other household members, which we observe in the form of joint activity participation and shared rides. Explicit representation of joint activity patterns is a widespread deficiency in extant travel forecasting models and remains a relatively under-developed area of travel behavior research. In this paper, we identify several spatially defined tour patterns found in weekday household survey data that describe this form of interpersonal decision-making. Using pairs of household decision makers as our subjects, we develop a structural discrete choice model that predicts the separate, parallel choices of full-day tour patterns by both persons, subject to the higher level constraint imposed by their joint selection of one of several spatial interaction patterns, one of which may be no interaction. We apply this model to the household survey data, drawing inferences from the household and person attributes that prove to be significant predictors of pattern choices, such as commitment to work schedules, auto availability, commuting distance and the presence of children in the household. Parameterization of an importance function in the models shows that in making joint activity-travel decisions significantly greater emphasis is placed on the individual utilities of workers relative to non-workers and on the utilities of women in households with very young children. The model and methods are prototypes for tour-based travel forecasting systems that seek to represent the complex interaction between household members in an integrated model structure.     

Modelling discretionary travel in the presence of imperfect data

The use of mathematical models in transportation and regional planning is limited by the need to obtain reasonably accurate, complete data sets. In particular complete spatial coverage is required for the usual discrete origin-destination models. Because of the time and cost constraints of obtaining such data, those charged with decision making responsibilities may choose to do without information that could be provided by quantitative models. This paper presents a procedure for estimating origin-constrained flows in situations where complete data collection is difficult or impossible. To this end an abstract model of origin-constrained travel is formulated. The required urban fields are constructed using interpolation and/or approximation techniques applied to available data. The tractability of the general model is demonstrated in the case of estimating the energy consumed in travel to existing or proposed facilities. The ability of the model to function with incomplete data was tested by using it to predict travel to the major retail centers located in the Albany-Schenectady-Troy Metropolitan Area.     

Strategies of developing part administration in Ireland

This paper reivews a programme recently undertaken by the Irish Government aimed at reforming the administration of Irish ports. Arising from that programme, and as a result of legislative changes, eight key ports were vested as commerical harbour companies (prior to this they were administered by large Boards and were very restricted in their ability to perform commercially). The context for the paper is the global trend towards port reformation, and the paper draws particuarly on the effects of the privatization of UK ports. The paper starts with a review of the role of parts, both generally and within the context of Ireland's growing, geographically peripheral, economy. Observations of the UK ports privatization process are next considered. The history, development and recent performance of Irish ports, together with port investment strategies, are critiqued and the background to the recent programme of administrative reform undertaken by the Irish Government concerning the ports is reviewed. Various observations from a number of sources (including 12 interviews by the authors with key actors in the sector) on the reform process are discussed. It is concluded that there is no uniformity of opinion as to the suitability of the chosen model for Irish ports administration and that it is too soon to judge whether it has been a success (the eight ports were commercialized in March 1997). The paper concludes that, given the critical role of ports within the Irish economy, the situation should be periodically reviewed to ascertain the current applicability of the extant port administration model.     

Suburbanization of jobs and the journey to work: A submarket analysis of commuting in the San Francisco bay area

Inrecent years, a debate has brewed over whether the decentralization of employment has been beneficial from a regional standpoint. In this article, we focus on one aspect of the debate: how the relocation of office workers from a downtown to a suburban location affects commuting patterns and mode choice. From a survey of 320 former downtown San Francisco workers who now work in the suburbs, we found that the average distance traveled remained essentially unchanged and that the average commuting speed increased. The most dramatic change, however, was the switch from public transit to drive-alone commuting. In the aggregate, we estimate that the change in job location was associated with nearly a threefold increase in vehicle miles traveled to work. While from a personal standpoint, employees seemed better off since they got to work faster and more comfortably, from a larger social and environmental perspective, the costs could be significant. More detailed analyses of commuter submarkets revealed that the transportation impacts vary considerably depending on whether the original residence was in the suburbs or central city and whether relocated workers had moved their residences in recent years. In general, those who remained in San Francisco and became reverse commuters were worst off whereas those who moved their residences out of the city were much better off in terms of job access. The article concludes that road pricing would be the best way to force motorists to internalize the external costs of increased drive-alone commuting. Second-best options would be to introduce development impact fees or employer-based trip reduction regulations.     

Japanese highway planning: A western interpretation

At the 1952 Census, less than 6 percent of national highways and prefectural roads in Japan were paved, and mechanically-propelled vehicles accounted for only 6 percent of total vehicle registrations; by 1981, 2792 km of expressway were in service (an addi tional 2623 km were under construction or being surveyed) and her industry was dominating world markets for motor vehicles. This paper, drawing on material translated from the Japanese language, examines the history of transport planning and engineering ideas that inspired the modernisation of the highway system in the period after the Pacific War. Three distinct phases are identified: (a) a politically and economically dependent Japanese state which borrowed methods from the U.S.A. in formulating 5-year national road programmes; (b) a more independent state, absorbing western techniques and refining them in 23 urban transportation studies; and (c) a donor state, exporting these ideas to Southeast Asian cities as one instrument of Japanese foreign policy. The triad of international antecedents, domestic context and content, and foreign application is a suitable framework when interpreting the intricate relationships between transport and society.     

The mid-Atlantic load centre: Baltimore or Hampton Roads?

Competition between closely situated seaports in not new. The ports of Baltimore and Hampton Roads, located at either end of Cheaspeake Bay, have been locked in a fierece battle to gain dominance in the lucrtice mid-Atlantic container traffic for a number of years. The probability that ech will succeed is not great, as shipping lines, concerned with the high costs associated with idle port time, will select one,rther thatn serve both. Indeed, evidence is beginning to mount that, dispite massive expenditures by the Stte or Maryland, the Virginia ports a reemerging as the region' load centre. This paper examines recent trends in container movements through these two major ports and suggests the long-termprospects for each. among measures considered are the location of eachi in relation to other ports both North and South, sizes of the port cities and their immediately adjacent hinterlands, proximity to inland population centres (markets), connectivity between the ports and these inland centres (by both rail and truck), expenditures by port agencies and land crries, labour relations, and availabillity of space for expansion.