Estimating travel time functions for urban roads: options and issues

Travel time functions specify the relationship between the travel time on a road and the volume of traffic on the road. Until recently, the parameters of travel time functions were rarely estimated in practice; however, a compelling case can be made for the empirical examination of these functions. This paper reviews, and qualitatively evaluates, a range of options for developing a set of travel time functions. A hierarchy of travel time functions is defined based on four levels of network detail: area, corridor, route and link. This hierarchy is illustrated by considering the development of travel time functions for Adelaide. Alternative sources of data for estimating travel time functions are identified.

In general, the costs and benefits increase as the travel time functions are estimated at finer levels of network detail. The costs of developing travel time functions include data acquisition costs and analysis costs. The benefits include the potential for reducing prediction errors, the degree of application flexibility and the policy sensitivity of the travel time functions.     

100%液态氟硅橡胶:一种耐燃油和机油的液态硅橡胶

氟硅橡胶(FVMQs)由于其独特的物性而使其需求量并未得到更大的增长.氟硅橡胶(FSRs)用于制造接触发动机燃料/汽车燃料.溶剂和机油的汽车产品,其用量正在不断增长.随着更多的生产商使用FSRs来生产产品,加工工艺的优化与零件的生产效率日益变得重要,但是这些问题却仍是难以解决的.     

International cooperation in Maritime casualty Investigations: an analysis of IMO RESOLUTION A.637 (1 6)

On 19 October 1989, the International Maritime Organization adopted a joint uslliberian resolution meant to advance international cooperation in maritime casualty investigations. This resolution reflected an international determination to achieve greater cooperation between different states in investigative matters, in a manner consistent with international law. This paper examines how the IMO resolution addresses some of the inherent problems in such a multi-national industry. It also examines the question of whether us lawmakers may, or should, impose stricter controls and restrictions unilaterally on foreign-flag ships which call on us ports.     

Liner shipping between East and West Europe: competitive developments in the Poland-United Kingdom trade

This paper provides an analysis of the development of the liner route between the UK and Poland and the activities of the two main operators—EuroAfrica of Poland and United Baltic Corporation of London. The most significant factors driving the development of this trade are analysed using a combination of an industrial survey and government statistics for the route, before going on to examine the threat to the trade presented by the growth of the trucking mode.     

Sustainability: A vital concept for transportation planning and development

The current pattern of metropolitan transportation and land development in the majority of countries around the world appears to be increasingly unsustainable from both an economical and environmental perspective. Many factors point to the need for adoption of a new paradigm for sustainable transportation and development in both high and low income countries—burgeoning populations, growing air pollution, limits on global petroleum reserves, limited physical and economic capacity to expand automobile-based transportation systems without community destruction, and the urgent need to limit global CO₂ emissions to slow the pace of global warming. This paper outlines some of the conceptual differences between the current paradigm for transportation planning and an emerging paradigm for sustainable transportation and land development. It compares the US and European patterns of transport and land development, which often inspire transportation decision-makers and planners in developing countries. The paper reviews the patterns of development in the cities of several developing countries, identifying policies than can enhance sustainability.     

Identification of potential sites for deep-ocean waste isolation with a geographic site-selection model

Identification of optimal sites for the isolation of waste on the abyssal seafloor was performed with two approaches: by the traditional method of map overlays of relevant attributes, and by a specially developed, automated Site-Selection Model (SSM). Five initial, Surrogate Sites, identified with the map-overlay approach, were then compared with the more rigorously produced scores from the SSM. The SSM, a process for optimization of site locations, accepts subjective, expert-based judgments and transforms them into a quantitative, reproducible, and documented product. The SSM is adaptable to any siting scenario. Forty-one factors relevant to the isolation scenario, including 21 weightable factors having a total of 123 scorable categories, have been entered into the SSM. Factors are grouped under project definition, unique environments, anthropogenic, geologic, biologic, weather, oceanographic and distance criteria. The factor scores are linked to a georeferenced database array of all factors, corresponding to 1°×1° latitude–longitude squares. The SSM includes a total of 2241 one-degree squares within 1000 n.m. of the U.S. coasts, including the western North Atlantic, the Gulf of Mexico, and the eastern North Pacific. Under a carefully weighted and scored scenario of isolation, the most favorable sites identified with the SSM are on the Hatteras and Nares Abyssal Plains in the Atlantic. High-scoring sites are also located in the Pacific abyssal hills province between the Murray and Molokai Fracture Zones. Acceptable 1° squares in the Gulf of Mexico are few and of lower quality, with the optimum location on the northern Sigsbee Abyssal Plain. Two of the five Surrogate Site locations, on the Hatteras and Sigsbee Abyssal Plains, correspond to the best SSM sites in each ocean area. Two Pacific and a second Atlantic Surrogate Site are located in low-scoring regions or excluded by the SSM. Site-selection results from the SSM, although robust, are an initial attempt to quantify the site-selection process. The SSM database exposes a significant lack of high-quality information for many areally mappable attributes on the abyssal seafloor, particularly bottom-current speed and measures of biologic productivity and flux. Terminologies and classifications of some measures, such as sediment types, suffer from parochialism and vary by ocean. Considerable research is needed even for a broad understanding of the environmental measures required to make sound societal decisions about use of the abyssal seafloor for disposal or other purposes.     

Devising business strategy for railways

This paper presents a case study which tackles a general problem for railway management, namely the formulation of a strategy to improve business financial performance. This is prefaced, in Section 2, by discussion of general principles - concerning the type of information system required, investigations to be conducted and associated measurement needs. The case study, of Section 3, concerns our investigations of VicRail's total business and its constituents. The task of financial improvement is revealed from an assessment of sectors' current cost-recovery positions and the identification of system joint costs. For freight sectors, future traffic prospects, pricing possibilities and the scope for more efficient operations are then considered, and the implications traced for overall deficit reduction and the development of business strategy. The concluding section draws some general lessons for railway managements.A fuller discussion by the authors of the theoretical framework employed, and particularly of the case study application, is contained in a complimentary publication: Improving Railway Financial Performance, published by Gower in January 1985.Transmark is a subsidiary of the British Railways Board, acting as its international consultancy. The authors, who were respectively study director and manager, wish to thank Bernard Warner (an independent consultant), Richard Eccles (of Transmark) and Adrian Balkyn-Rackowe (of British Rail) for their valuable contributions. The study report, titled Rail Cost — Pricing Options, was released by the Minister in April 1981.     

Equilibria of bilateral taxi–customer searching and meeting on networks

This paper proposes an equilibrium model to characterize the bilateral searching and meeting between customers and taxis on road networks. A taxi driver searches or waits for a customer by considering both the expected searching or waiting time cost and ride revenue, and a customer seeks a taxi ride to minimize full trip price. We suppose that the bilateral taxi–customer searching and meeting occurs anywhere in residential and commercial zones or at prescribed taxi stands, such as an airport or a railway station. We propose a meeting function to spell out the search and meeting frictions that arise endogenously as a result of the distinct spatial feature of the area and the taxi–customer moving decisions. With the proposed meeting function and the assumptions underlying taxi–customer search behaviors, the stationary competitive equilibrium achieved at fixed fare prices is determined when the demand of the customers matches the supply of taxis or there is market clearing at the prevailing searching and waiting times in every meeting location. We establish the existence of such an equilibrium by virtue of Brouwer’s fixed-point theorem and demonstrate its principal operational characteristics with a numerical example.     

Determining intermediate origin-destination matrices for the analysis of composite mode trips

We consider in this paper the problem of determining intermediate origin-destination matrices for composite mode trips that involve a trip by private car to a parking facility and the continuation of the trip to the destination either by walking or by a transit mode. The intermediate origin-destination matrices relate to each component of the composite mode trip: a matrix from the trip origins to intermediate destinations which are parking lots and a matrix from the parking lots to the final destinations. The approach that we propose to solve this problem is to modify the entropy based trip distribution models to consider inequality constraints related to parking lot capacities. Such models may be easily calibrated by using well known calibration methods or generalization of these methods and may be easily solved by applying a primal feasible direction method of nonlinear programming.