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行程时间的不确定性是影响货运车队路径选择的一个重要因素，特别是对于要求货物准时送达的配送任务（例如商品混凝土的配送），提出了在车辆调度中考虑由拥挤路段交通流量波动引起的行程时间不确定性的方法，建立了考虑行程时间可靠性要求的车辆优化调度数学模型，给出了相应的启发式算法，通过算例介绍了该模型和算法的应用。结果表明配送总成本随行程时间可靠性要求的提高而增加。     

Modeling oil spills in a river—lake system

A general model shell, ROSS3, is developed for simulating oil spills in complex river systems using techniques which have not been previously exploited in oil spill models. ROSS3's new approach has several advantages over the approach to model oil spills in the past: (a) The use of a time-varying boundary-fitted coordinate system that allows accurate accounting for complex river/lake boundary as well as the river boundary changes as its water levels fluctuate; (b) The ability to confine two-dimensional hydrodynamic computations to a limited river reach; (c) The ability to interactively layout the channel networks for setting up the model, define extra cross sections to increase the accuracy if needed, in addition to the traditional data entry and visualization interfaces.ROSS3 is a two-layer two-dimensional oip spill model that can simulate the mechanism of advection, horizontal diffusion, mechanical spreading, shoreline deposition, evaporation, dissolution, vertical mixing, resurfacing and sinking. In ROSS3 spilled oil may be a surface slick or suspended oil droplets, or a combination of both. Both free surface and ice cover conditions can be simulated. The flow of conditions can be varied and the unsteady flow model can be run within ROSS3 to simulate the flow conditions in both the river and the lake. The ice conditions can be added or removed from the model input using easy interactive procedures.     

The allocation of buses in heavily utilized networks with overlapping routes

Many transit systems outside North America are characterized by networks with extensively overlapping routes and buses frequently operating at, or close to, capacity. This paper addresses the problem of allocating a fleet of buses between routes in this type of system; a problem that must be solved recurrently by transit planners. A formulation of the problem is developed which recognizes passenger route choice behavior, and seeks to minimize a function of passenger wait time and bus crowding subject to constraints on the number of buses available and the provision of enough capacity on each route to carry all passengers who would select it. An algorithm is developed based on the decomposition of the problem into base allocation and surplus allocation components. The base allocation identifies a feasible solution using an (approx.) minimum number of buses. The surplus allocation is illustrated for the simple objective of minimizing the maximum crowding level on any route. The bus allocation procedure developed in this paper has been applied to part of the Cairo bus system in a completely manual procedure, and is proposed to be the central element of a short-range bus service planning process for that city.     

Preliminary results from an integrated transportation and land use models package

This paper describes the results, to date, of an effort to integrate a land use model with a transportation network model for the purpose of analyzing the interrelationships of transportation facility development and land development. In the system which has been developed each model provides input to, and receives feedbacks from, each other model. To the author's knowledge, the effort described here represents the first successful attempt to develop and test an integrated model package involving these reciprocal relationships. The results obtained from preliminary runs of this package should be of considerable interest to both transportation planners and land use planners. With this integrated system it has been possible to observe the interrelationships, and in particular the feedbacks, between land use and levels of traffic on the networks. Preliminary results indicate that congested networks produce tendencies toward metropolitan centralization. Attempts to relieve congestion seem to produce metropolitan decentralization and increased travel which lead, in turn, to metropolitan sprawl and increased spread of congestion.     

The Dutch mobility panel: Experiences and evaluation

The aim of this paper is to give an overview of the history and research experiences of the Dutch National Mobility Panel. Attention is given to the sampling strategy, the policy goals, and the representativity of the panel. It also tries to evaluate the research outcomes in terms of the original objectives and in view of more general research and policy goals. In sections one and two, a historic overview is given, starting from the first ideas to implement a longitudinal research instrument in transportation planning. In section three, some attention is devoted to longitudinal versus cross-sectional analyses. In section four, the sample design is treated in some detail. Next, various forms of bias are discussed that affect the representativity of the panel. In the sixth section, an overview is given of the research conducted with the data. Some conclusions are given in the final section.     

Modelling the ice-ocean-plankton interactions in the Souther Ocean

Our goal is the study of interactions between sea ice and ocean and of their influence on planktonic communities. We use a physical model which includes explicitly melting dynamics and mixed-layer physics. A one-dimensional model of the water column with a k-1 turbulent closure is applied. The sea-ice model is the one proposed by Semtner (1976); we add a parameterization of leads. We enlighten the importance, in this kind of model, of the sharing of the energy between lateral and basal meltings. The biological model comprises two state variables: phytoplankton and zooplankton biomasses. Melting induces a persistent shallow mixed layer and thus appropriate conditions for primary production. If ice melting is present, high biomasses are possible even with high losses. The absence of ice nearly forbids a massive bloom to form. Some sensitivity studies have shown that grazing pressure is a key factor governing the evolution of biomasses. The biomasses are also sensitive to little modifications of the photosynthetic production. The initial amount of phytoplankton or the presence of ice algae seems to be of lesser importance.     

Design of Optimal Four-Wheel Steering System

Optimal design of the four wheel steering (4WS) system of the ground vehicle is studied. 4WS vehicles with the optimal control scheme are considered first. General formulation of the optimal control law is developed based on the linear quadratic regulator theory. The vehicle speed function (VSF) based 4WS vehicle with a simple feedback controller is considered as a special case of the optimal system. Two new designs of the VSF 4WS system are proposed and their performances are compared with the optimal 4WS systems and the existing VSF 4WS system. The first system is designed for the maximum stability while the second system is designed to emulate the response of the optimal 4WS vehicle. Advantages of the new VSF designs are discussed.