Discretionary activity time allocation of individuals between in-home and out-of-home and between weekdays and weekends

This paper formulates a model for the allocation of total weekly discretionary time of individuals between in-home and out- of-home locations and between weekdays and the weekend. The model formulation takes the form of a continuous utility-maximizing resource allocation problem. The formulation is applied to an empirical analysis using data drawn from a 1985 time-use survey conducted in the Netherlands. This survey gathered time-use information from individuals over a period of one week and also collected detailed household-personal socio-demographic data. The empirical analysis uses household socio-demographics, individual socio-demographics, and work-related characteristics as the explanatory variables. Among the explanatory variables, age of the individual and work duration during the weekdays appear to be the most important determinants of discretionary time allocation.     

Robust Stability Analysis of LQG-Controlled Active Suspension with Model Uncertainty Using Structured Singular Value, μ, Method

This paper presents a systematic approach toward robust stability analysis of LQG-con trolled active suspension systems. To perform this task, the paper starts with a brief background information on LQG control, its relation to H₂ method, and showing how H₂ could be formulated to become the frequency domain equivalent of LQG. Then unstructured and structured uncertainties of active suspension are formulated. The paper continues with the definition of maximum singular values and structured singular values of a transfer function matrix. Using these definitions, the robust stability of an active suspension system in the presence of assumed parameter variations are analyzed. These steps are illustrated by means of a numerical example of an active suspension system.     

Two-Dimensional Contact Area of a Pneumatic Tire Subjected to a Lateral Force

A mathematical model of a two-dimensional contact patch of pneumatic tires rolling over a rigid flat road surface at arbitrary slip and camber angles has been developed. The model is simple in concept, contains few parameters and is applicable to any tire simulation models. In addition to tire geometric parameters and vertical deflection, the carcass camber angle is introduced in the model. This angle is alone responsible for the asymmetric shape of the tire contact patch when the tire undergoes a lateral force. The computed contact patches agree well with the measured patches of an automotive tire at different slip and camber angles. Lastly, the influence of the contact patch geometry on the tire cornering and aligning properties has been discussed through a computational example. It has been shown that the effect of tire contact patch geometry on the steady state behavior is rather remarkable.     

Specifications for a new long-range urban transportation planning process

This paper asserts the continuing need for a long-range component to urban transportation planning, citing particularly the relationships between short- and long-range planning and the dangers of a single-minded concentration on short-range planning. However, the nature of the long-range planning procedure that is required is substantively different from that of most extant approaches. Some of the specific requirements and capabilities of a new procedure are described, and existing procedures are compared against these.In the latter part of the paper, some of the elements of a new long-range planning procedure are characterized. It is suggested that the procedure be built around a scenario approach to confronting and bounding future uncertainty. Second, the need to incor porate financial forecasting in the process is laid out and related to the scenario concept. Third, the need for travel- and impact-forecasting procedures is recognized and a set of input, output and operating requirements for such procedures are specified. It is suggested that improved sketch-planning tools may fit the requirements to a large extent. It is also suggested that some procedures or models in the process should be synthetic models, not needing calibration for each new application. Finally, a number of requirements are specified for the display and evaluation of planning proposals from this procedure. A major emphasis is placed here on transparency of the process and responsiveness to direct intervention by the decision-maker.     

Editorial: Young maritime researchers—a note of respect

Globalization, liberalization, competition and spatial interaction are significant factors affecting the transformation of manufacturing industries worldwide. In the transportation and logistics industry, however, cooperation is becoming even more critical than competition in determining firms' efficiency. Cooperation has always characterized the liner sector in which strategic alliances, mergers and acquisitions have generated twin effects: notable increases in ship size and falls in freight rates. Meanwhile, the stevedoring industry is undergoing privatization-driven consolidation and the emergence of global pure terminal operators. This article focuses on vertical integration between global carriers and terminal operators. We address the following key current issues: 1. dedicated terminals as a strategy for cutting costs and controlling integrated transport chains;

2. the struggle for supply chain control, involving global carriers versus global terminal operators, driven by financial power and technical and managerial capability.

We close analysing one of the core problems of the market, namely the evolving role of the dedicated terminals. For the pure stevedores they represent an opportunity to secure a cargo, while in the hands of the liners they enable cost stability and the possibility to put pressure on pure terminal operators.     

Liner costs and pricing polices: a reconsideration of regulatory issues

A number of shipping analysts have adopted as a convenient approximations, the assumption that linear costa are homogeneous per unit of cargo. The paper points to recent evidence suggesting that considerable differences exist in the estimates of implicit marginal cost for various types of cargo, and re-evaluates the regulatory arguments which are based on the assumption of homogeneity of costs.     

Risk assessment: An introduction and critique

Abstract

Risk assessment is a methodology which has been used to evaluate the safety of major public projects, notably aerospace programs, liquefied natural gas import facilities, and nuclear power plants.

This article begins with a review of public attitudes toward risk and then describes the basic components of a risk assessment. Subsequent critical analysis suggests the pitfalls inherent in the technique, especially in regard to the establishing of a criterion of safety against which the results of a risk assessment will be compared. The author identifies three such criteria and rejects two of them, including the one most commonly used in federal government agency decision‐making, as unreliable or philosophically unacceptable.

The article concludes with comments on the applicability of risk assessment in coastal zone management.     

A stochastic model for highway traffic

A nonlinear model for unidirectional flow of heavy traffic on a two-lane highway is considered. Features such as entrance, exit and lane transfer with time-dependent parameters are incorporated into the model, with the result that a number of previous models employed in the study of traffic flow become special cases of ours. Using the method of system-size expansion, an asymptotic analysis of the problem, including the time evolution of both deterministic and stochastic aspects of the traffic system, is carried out. In addition, a scheme for obtaining the moments of the probability distribution for systems of finite size is developed and a comparison is made with the exact results appropriate to a particular model. The agreement between the two sets of results turns out to be remarkably good.     

Comparative environmental impacts of electric bikes in China

Electric two-wheelers have become a significant mode of transportation in China in the past decade. Though marketed and publicized by some as zero-emission vehicles, little past research has been done to quantify the environmental impacts of electric two-wheelers in China. This paper quantifies some of the environmental impacts of the production processes and use phase of electric two-wheelers and compares them to the environmental impacts of competing modes, including bicycles, buses, motorcycles and cars. The use phase emissions are quantified geographically with significantly higher emissions in coal rich regions, compared to regions relying more on hydropower. The results show that electric two-wheelers emit several times lower pollution per kilometer than motorcycles and cars, have comparable emission rates to buses and higher emission rates than bicycles. Lead is one pollutant on which electric two-wheelers perform poorly, because of their use of lead acid batteries.