Link choice proportions from trip distribution and assignment models: An overview and comparison

A number of estimation procedures have been suggested for the situation where a prior estimate of an origin-destination matrix is to be updated on the basis of recently-acquired traffic counts. These procedures assume that both the link flows and the proportionate usage of each link made by each origin-destination flow (referred to collectively as the link choice proportions) are known. This paper examines the possibility and methods for estimating the link choice proportions. Three methods are presented: (1) using ad hoc iteration between trip distribution and traffic assignment; (2) combining trip distribution and assignment in one step; (3) solving a new optimization problem in which the path flows are directly considered as variables and its optimal solution is governed by a logit type formula. The algorithms, covergencies and computational efficiencies of these methods are investigated. Results of testing the three methods on example networks are discussed.     

Characteristics of Guided-Steering Railway Trucks

The dynamic characteristics of guided-steering railway trucks are described both in a general sense and in terms of a specific design. Stability margins and curving performance have been predicted and are compared for both conventional and steered vehicles. It is shown that guided-steering trucks exhibit modes of instability which, although surmountable by proper design, are not found in conventional trucks. In particular, a low conicity, divergent, leading truck instability is described together with a companion high conicity, divergent trailing truck instability. Curving and dynamic performance for steered vehicles is shown to have the potential of being far superior to that of comparable conventional vehicles. Factors influencing the design of steered rail vehicles are presented and discussed.     

PC—NFS双向资源共享的后台服务进程方案

在计算机网络系统中,信息的分布存储和处理是一个重要方面,也是计算机网络必须提供的一种服务。Sun ONC网络环境中的PC—NFS基于单用户、单任务的PC—DOS操作系统,仅实现了单向的文件资源共享,我们提出了一种网络后台服务进程的方案,实现了服务器和PC机之间的双向资源共享,完善了PC—NFS通信软件的功能。     

Junction interactions and monotonicity in traffic assignment

We consider the traffic equilibrium problem when the travel demand is inelastic and stationary in time. Junction interactions, which abound in urban road networks, are permitted. We prove that the set of equilibria (solutions to the assignment problem) is convex when certain monotonicity and continuity conditions are statisfied at each junction.     

A Study of the Response of a Double Bottom Vehicle to Steering and Braking

The paper describes the development, operation and some of the results obtained from a simulation of the steering behaviour of the double bottom articulated vehicle, in particular the effects that arise when certain axles are locked.     

Structural change in anglo-continental Ro-Ro traffic, 1977-1987

Elementary and generalized specialization indexes are used to detect structural change and its processes in the Ro-Ro traffic between the United Kingdom and Continental Europe. Powered vehicles dominate British exports through Channel and Straits ports, whereas unaccompanied trailers have the lead for traffic through North Sea ports. A major structural change took place on the continental side, where both forms of traffic came to a new balance in the Belgian ports between 1977 and 1987 in an otherwise stable market share context.     

Aspects of the stability of jack-up spud-can foundations

A three-level procedure for assessing jack-up foundation stability for more or less homogenous soils is described. The objective is to provide a rational framework for these assessments that ensures their safe operation in extended year-round operations and enables their use in deeper waters than at present.

The three levels of the procedure have to be entered successively as long as foundation stability cannot be proven. The first level is a screening exercise and essentially replaces the well-known preload check. The second level compares factored foundation loads resulting from a structural analysis with foundation capacities obtained with ultimate bearing capacity formulae. The most refined third level assesses whether the displacements associated with these loads lead to an acceptable situation, i.e. capacity increase and/or load redistribution that does not result in collapse of the jack-up unit.

Since, for maximum benefit, this third-stage analysis requires a non-linear foundation model to be linked with the structural package used: such a tool is provided in the paper. Examples are given to demonstrate the impact of the assessment procedure.

This procedure forms part of the overall in-house approach to the assessment of jack-ups and has already been offered to the jack-up industry as part of the continuing efforts towards establishing common and accepted standards for jack-up assessments. Further developments have been identified and will be pursued.     

Application of Inverse Models to Vehicle Optimization Problems

This paper presents a nonlinear inverse model of a road vehicle which simulates combined steering and braking/driving. The inputs to the model are the lateral and longitudinal acceleration of the vehicle's sprung mass center. The simulation returns the steering wheel angle and brake/drive torques required to obtain the desired accelerations. An example is presented which demonstrates the utility of inverse models for optimization purposes.     

A computer model for finding the time-dependent minimum path in a transit system with fixed schedules

This paper describes the development of a computer model and algorithms for finding the time-dependent minimum path between two stations in a multi-route, multi-mode transit system running to fixed schedules. Selection of the minimum path can be based either on journey time or on weighted time. A worked example using a simple transit network is given to illustrate how the model works. The model has several applications in transport planning: it can be used for generating route schedule information to guide transit users, for assisting in route schedule coordination, and for analyzing transit system accessibility.