Simulation and Visualisation of the Dynamic Behaviour of an Overhead Power System with Contact Breaking

For high speed rail traffic it is necessary to design overhead power systems which minimize the contact loss between pantograph head and contact wire. To predict how different design solutions will behave it is favourable to model and simulate the dynamic behaviour. In this paper a model of an overhead power system is specified and used in simulation. The model is suitable for simulation with contact loss since it includes specifications of impact conditions between pantograph head and contact wire. Two sets of equations of motion are specified, one for the contact case and one for the non-contact case. The model also includes lateral movement of the wire due to the zigzag span and friction between the pantograph head and the contact wire. It is shown how to make animations of the system behaviour using a MCAE-system. The animations are made using a geometrical model of the system together with results from numerical simulations.

Through the examples provided, use of the mathematical model and the geometrical model is presented. The response is visualised as time histories and phase plane diagrams of different coordinates and as animations of the total system response. The different types of visualisations make an excellent combination when studying the system behaviour of different design solutions.

In one example, simulation using the linearised set of equations gives the same results as simulation using the set of fully nonlinear equations, due to periodic response and the simple alternation of contact conditions. It is shown that the situation when any of the parameters vary suddenly is possible to simulate using the fully nonlinear equations of motion.     

The influence of transportation improvements on interregional trade in Brazil

In this study the impact of transportation improvements on Brazilian interregional commodity flows are considered. The decreasing friction of distance is measured by two variants of the gravity model. First, distance coefficients are calculated for trade among all states in 1942 and 1962. Second, distance coefficients for each state's imports are calculated separately and then related to state per capita income, for the year, 1962. Both the time-series and cross-section results indicate a significant diminution in the friction of distance in the course of Brazilian development. The degree to which trade has integrated the national economy is assessed by the convergence of agricultural prices. Not only have interregional price differentials tended to diminish, but regional price structures are becoming more similar. The interrelation of these price structures provides a method of regionalizing the Brazilian space-economy.Most of the data for this study were collected during the author's tenure as Ford Foundation Visiting Professor at Instituto de Pesquisas Economicas, Universidade de Sao Paulo, Brazil. The Milton Fund and the Department of City and Regional Planning, both of Harvard, sustained the completion of this research. Milton Campanario and Abby Rashid provided invaliable assistance in assembling the data. Jeffrey Dutton of the Harvard Laboratory for Computer Graphics provided a program for calculating distances. William McAuliffe suggested some imaginative interpretations of the factor analysis.     

Attitudinal and situational variables influencing urban mode choice: Some empirical findings

A mode choice decision structure incorporating traveler attitudes toward modes and situational constraints is investigated. The major hypothesis tested is that mode choice is determined primarily by situational constraints, such as auto ownership and income, secondly by the quality of alternative modes.The structure of the mode choice process is analyzed with respect to (1) applicability of certain choice criterion forms; (2) psychological weighting of modal attributes in the choice criterion; (3) strength of logit, probit, and discriminant functional forms; (4) the relative strength of socio-economic and attitudinal variables in predicting mode choice. An evaluation is made of 50 binary choice models fitted to a sample of 471 randomly drawn urban travelers. Results indicate that (1) the four choice criterion forms tested are all about equal in predictive strength; (2) psychological weighting has no effect on model strength, but does influence which modal attributes appear to determine choice; (3) the three functional forms tested are all about equal in strength; (4) situational factors account for 80–90% of variation explained by the models, attitudes toward modes 10–20%, thus confirming the primary hypothesis. Implications of these results for mode choice modeling and transit planning are discussed.This paper summarizes current research at the New York State Department of Transportation on the motivations and causes of travel behavior. Complete findings are available in Hartgen (1973).     

Characterization of Dynamic Vehicle Stability Using Two Models of the Human Pilot Behaviour

This article deals with a study of the stability of the vehicle/pilot system for two different models of human operator behaviour. These models, are the outcome of various.approximations of the precision model for single loop compensatory situations. The vehicle is represented with two degrees of freedom and the pilot is assumed to respond to the lateral displacement and to the lateral velocity with a time delay. The properties of these resulting systems are presented and it is observed that, for any given forward visibility, a critical velocity defines a domain of controllability from a domain of uncontrollability. Furthermore this critical velocity is shown independant of the vehicle/ pilot parameters and may be considered as a possible vehicle safety criterion.     

Estimating bus run times for new limited-stop service using archived AVL and APC data

In recent years, several transit agencies have been trying to be more competitive with the automobile to attract choice riders. Transit agencies can only be competitive if they can provide services that are reliable, have a short access and egress time, and have run times that are comparable to automobiles. Several transit agencies try to be competitive through offering faster service, such as limited-stop (express) bus service. This study uses AVL and APC data, in addition to a disaggregate data obtained from a travel behavior survey, to select stops and estimate run times for a new limited-stop service that will run parallel to a heavily used bus route (67 Saint-Michel) in Montréal, Canada. Three different scenarios are developed based on theory and practice to select stops to be incorporated in the new limited service. The time savings for each scenario are then evaluated as a range and a fourth scenario is developed. A limited-stop service is recommended based on selecting stops serving both directions of the route, major activity points and stop spacing. This study shows that implementing a limited-stop service would yield substantial time savings for both, the new limited service and the existing regular service running in parallel.     

African shippers' organizations: the Ghanaian experience

This paper looks at how the Shippers‘ Council could operate to make shipping cost-effective and to play its role as a servant of trade—a servant of the shippers. It looks at the key problems that confront the shipper requiring intervention by a Shippers‘ Council and surveys how the organization of the Shippers’ Council effectively handles problems. The final sections draw conclusions which could contribute to increasing the efficiency of Shippers' Councils, as well as improving the understanding of the Councils as managers of the demand side of shipping.     

The measure of all things: reflections on changing conceptions of the individual in travel demand modeling

Transportation demand modeling has evolved in scope, theory, and practice in the many decades since the US Bureau of Public Roads pioneered home interview transportation studies in metropolitan households in the early 1940s. The major currents of these developments are discussed in the present paper through consideration of the changing role of the individual—as a source of data, as a unit of analysis, and as the intended beneficiary. In addition to reviewing this history we raise, but are unable to resolve, a growing current concern, namely how the public interest can be best served when the transportation data of greatest value is collected by private entities.     

The crisis for transportation planning modelling

The paper considers the performance of land‐use transportation study techniques over the past ten years. Although primarily viewed from a U.K. perspective the paper reviews matters of principle which are of international relevance. The changing context and tasks for modelling are reviewed and the current role and applications of such models considered. The capability of established models to meet these changing requirements is examined. Attention is drawn to model specification and the ability of models both to represent new policies and to predict traveller responses to them. Also relevant is the ‘behavioural’ theme and the way in which survey technique conditions the data obtained.

Particular emphasis is placed on the accuracy of modelling, both in the representation of base year travel patterns and in the forecast mode. The inherent uncertainty concerning input data is discussed and the frequent failures to establish model validity are noted.

Three crises for U.K. transportation planning practice are identified: the ageing of data bases, the accuracy and validity of models and the current changes to the institutional context of transport planning in the U.K. Some potential remedies for the first two difficulties are proposed. It is concluded that only the last ‘crisis’ represents a real threat to the application of rational methods in transportation planning.     

Linking mercury exposure to habitat and feeding behaviour in Beaufort Sea beluga whales

Mercury (Hg) levels in the Beaufort Sea beluga population have been increasing since the 1990's. Ultimately, it is the Hg content of prey that determines beluga Hg levels. However, the Beaufort Sea beluga diet is not understood, and little is known about the diet Hg sources in their summer habitat. During the summer, they segregate into social groups based on habitat use leading to the hypothesis that they may feed in different food webs explaining Hg dietary sources. Methyl mercury (MeHg) and total mercury (THg) levels were measured in the estuarine-shelf, Amundsen Gulf and epibenthic food webs in the western Canadian Arctic collected during the Canadian Arctic Shelf Exchange Study (CASES) to assess their dietary Hg contribution. To our knowledge, this is the first study to report MeHg levels in estuarine fish and epibenthic invertebrates from the Arctic Ocean. Although the Mackenzie River is a large source of Hg, the estuarine-shelf prey items had the lowest MeHg levels, ranging from 0.1 to 0.27 μg/g dry weight (dw) in arctic cisco (Coregonus autumnalis) and saffron cod (Eleginus gracilis) respectively. Highest MeHg levels occurred in fourhorn sculpin (Myoxocephalus quadricornis) (0.5 μg/g dw) from the epibenthic food web. Beluga hypothesized to feed in the epibenthic and Amundsen Gulf food webs had the highest Hg levels matching with high Hg levels in associated food webs, and estuarine-shelf belugas had the lowest Hg levels (2.6 μg/g dw), corresponding with the low food web Hg levels, supporting the variation in dietary Hg uptake. The trophic level transfer of Hg was similar among the food webs, highlighting the importance of Hg sources at the bottom of the food web as well as food web length. We propose that future biomagnification studies incorporate predator behaviour with food web structure to assist in the evaluation of dietary Hg sources.