Pollution history of a tropical estuary revealed by combined hydrodynamic modelling and sediment geochemistry

Hydrodynamic modelling of water movement in Hunts Bay, a protected part of Kingston Harbour, Jamaica, shows that depth averaged tidal flows are very low. In the northeast corner of Hunts Bay, water is essentially stagnant. Even under high flow conditions, much of the Bay bottom water is ‘bypassed' by buoyant, lower salinity surface flows. The muddy sediments of Hunts Bay reflect these sluggish to stagnant conditions; sediment cores from the northeast corner of the Bay contain progressively higher amounts of organic matter in their upper parts (last 15–20 years sedimentation). Combined C/N ratios and stable carbon isotope compositions of this organic matter imply a sewage origin. Both lead and chromium metal concentrations and enrichment factors relative to average crustal shales show geographically related patterns that reflect hydrodynamic circulation predicted by modelling. In particular, metal concentrations and enrichment factors are highest at the northern end of the bay, especially in the northeast corner. Modelling confirms that stagnant conditions would occur in the northeast part of the bay even without the presence of a major causeway. The causeway may contribute to low flow conditions, but is not the principal cause of organic contamination, which is simply an excessive input of sewage.     

A retrospective and prospective survey of time-use research

The central basis of the activity-based approach to travel demand modeling is that individuals' activity-travel patterns are a result of their time-use decisions within a continuous time domain. This paper reviews earlier theoretical and empirical research in the time-use area, emphasizing the need to examine activities in the context or setting in which they occur. The review indicates the substantial progress made in the past five years and identifies some possible reasons for this sudden spurt and rejuvenation in the field. The paper concludes that the field of time-use and its relevance to activity-travel modeling has gone substantially past the "tip of the iceberg", though it certainly still has a good part of the "iceberg" to uncover. Important future areas of research are identified and discussed.     

The experience of express coach deregulation in Great Britain

This paper reviews the effect of express coach deregulation in Britain following the Transport Act 1980. The authors have monitored the range of services offered before and after the Act, using operators' literature, roadside surveys, on-vehicle passenger interviews and interviews with operators as sources of information. These are used to present an overall picture of express deregulation, with particular reference to changes in real fare levels, and also the relative importance of competition within the coach industry compared with that of inter-modal competition (that between coach and rail). The latter has emerged as more significant.The greater part of the paper is devoted to analysis of the long-distance market but the development of commuter coach services into central London is also examined, together with the reasons why independent operators have secured a larger share of this market.     

Measuring the benefits derived from a transportation investment

This paper reviews the problems associated with application of the concept of consumers' surplus to the measurement of benefits derived from a transportation investment. This review is warranted since such measurement is very complicated when alternative modes or different paths are available to the users and benefit measures have been proposed which, on the surface, appear not to agree. In particular, as Mohring (1976), Williams (1976) and Agnello (1977), among others, have discussed, demand curves for interdependent modes will shift in response to a modal specific improvement, i.e. a unimodal investment, thereby complicating the measurement of consumers' surplus. The perspective taken in this paper resolves seeming inconsistencies in the literature regarding the directions of demand shifts and the correct measure to be used in calculating changes in consumer's surplus following an investment. This is accomplished by introducing an aggregate, origin-destination demand curve which is independent of the alternative modes actually available and from which traditional modal demands can be derived. An approach for deriving the modal demands from the aggregate demand and the behavioral assumptions behind the aggregate supply is described; the aggregate demand is used to unequivocably determine the directions of shifts in the modal demand curves due to specific modal investments. The resulting consistency of modal and aggregate demand is shown to lead to an unambiguous measure of total consumers' surplus variation. Extensions to include producers' surplus are also given.     

Economic policies and seaports: Are port authorities necessary?

This paper first presents arguments for having public sector port authorities. They can deal, flexibly and permanently, with property rights within their own areas. They can plan and regulate port areas comprehensively. They can provide 'public goods'. They can deal, in various ways, with externalities. They can promote efficiency, whether their own (if they operate as a comprehensive port) or that of the private sector (if they are largely landlords). For example, if their policy is to rely on the private sector to produce efficiency through competition then they can see to it that there actually is competition and not any kind of cartel or monopoly. Examples are cited where this last function has not been performed. The exception for single-user ports is noted.

Against them are the general disadvantages of public authorities (or bureaucracies)—though examples are cited where port authorities had very small staffs. The common instances of 'market failure' may thus be contrasted with those of 'government failure'. Finally, a pragmatic approach is advocated, tailored to the needs and resources of the country in question. The increasing effect of the economies of scale in port technology, and its limitation on competition, is, however, noted and to be discussed in the next paper.     

俄罗斯、日本及北美等国钢轨焊接工艺和设备的分析

文章介绍了俄罗斯、日本和北美等国和地区在轨道焊接方面的焊接工艺、方法和设备。特别详细阐述了几种焊接方法的优、缺点,并作了试验和实际比较。文章指出：就钢轨焊接质量和生产效率而言,闪光焊（接触焊）是最佳的,但就焊接成本而言,它并非是最佳的。因为其设备制造成本昂贵,且钢轨的焊接损耗较大。另外,从经济角度上来考虑,在既有线和新线上进行焊接时也应该采用不同的焊接方法和工艺。文章指出：在新线上采用闪光焊（接触焊）是比较经济和合理的。同时也介绍了世界上一些著名的钢轨焊接设备制造公司及其产品。     

A review of separate and joint strategies for the use of data on revealed and stated choices

This paper examines recent developments in household travel surveys that collect data for use in transportation planning and modeling efforts. The paper then introduces the notion of a total survey design and elaborates on what is meant by this concept. This is done first in the context of standard surveys of revealed choices. The paper discusses aspects of content and respondent burden and illustrates the potential to reduce respondent burden through careful consideration of content, question design, and question ordering. The paper also explores some issues of survey "friendliness" particularly with respect to activity surveys versus time-use surveys, with some observations about the potential of time-use surveys to eliminate some of the burden and content problems of previous diary designs. The remainder of the paper concentrates on the issue of collecting stated-response data and examines two alternative methods for collection: simultaneous collection of the contextual information and "on-the-fly" development of the alternatives for the stated-response questions, or sequential collection of contextual data and development of the stated-response questions. The paper also addresses issues of respondent burden that arise in the administration of stated-response surveys. The paper concludes with exploration of some of the reasons for collecting stated-response data, with particular emphasis on the US situation. In conclusion, the paper stresses again the need for a total design concept for collection of stated-response data, as well as for the simpler collection of more standard revealed choice data.