Characterization and evolution of spatial density patterns in urban areas

This paper examines the spatial patterns of population density, household automobile ownership and other socio-demographic variables that affect urban travel, as a function of distance from the central city core. Spatial density functions provide a useful characterization of urban structure, and of its evolution when taken at different time intervals. Analysis of the data from four case cities (Austin, Atlanta, Dallas, Phoenix) for 1960, 1970 and 1980 reveals continuing overall dispersion away from the traditional central core, accompanied by the densification of formerly low-density suburbs. This presents implications for high congestion levels in the densifying suburban communities, comparable to those typically associated with the CBD. In addition, the analysis has captured the continuing growth of average household automobile ownership and revealed a distinct spatial pattern that seems to be robust across the case areas considered, as well as within radial corridors in the one case that was so analyzed (Austin).List of symbols Y gross population density in census tractt - X _t distance in miles from the center of tract to the CBD - parameter representing the central business district density - y density gradient parameter - X₀, X₁, X2, and X3 locations of the knots in a three segment division of the x-axis - D_i dummy variable defined for thei-th segment - ₁ normally distributed disturbance term,a _i,b _i,c _i,d _i,i = 1, 2, 3 — parameters to be estimated - A _t area of census tractt     

Dynamic location: an iconic model to synchronize temporal and spatial transportation data

This paper describes a model to synchronize the management and query of temporal and spatially referenced transportation data in geographic information systems (GIS). The model employs a method referred to as dynamic location, which facilitates spatial intersect queries from geographic shapes without the use of topological relationships. This is the inverse of how dynamic segmentation works in GIS. In contrast to dynamic segmentation, dynamic location stores geometry as an object within a single database field. This is an efficient, precise iconic model superseding the need for data decomposition into a complex set of tables. As an object model, the dynamic location process lends itself to high performance in an Internet, data-intensive, enterprise environment. Linear events are stored as {x, y} features, and not referenced to any route system. Route systems are built from {x, y, m} values (m for measure) and serve as number lines for mathematical operations. Any {x, y} object can then be referenced to either the Cartesian grid or any selected number line. This method offers the benefits of linear referencing, while making full use of a stable geodetic datum. Combinations of any {x, y} events may be placed over any {x, y, m} number line (route) and an intersect determined by looking through stacked {x, y, m} vertices of the coincident shapes. Since both geometry and shape reside in the same record, the use of “begin” and “end” dates facilitates full spatial and temporal version control. From a business process perspective, this creates a spatially enabled database, pulling GIS business functions back into the information technology mainstream.     

Upwelling mechanisms in the northwestern Alboran Sea

From April 1996 to July 1997, a series of hydrographic surveys were carried out in the Northwestern part of the Alboran Sea to investigate the upwelling that is an almost permanent feature in this area. Simultaneously a mooring line was deployed in the north part of the eastern section of the Strait of Gibraltar to monitor the variability of the Atlantic Jet (AJ). Two mechanisms are shown to be relevant for the upwelling dynamic in the region: the southward drifting of the AJ and wind stress. A linear relation between the angle under which the Jet enters the Alboran Sea and the distance from the coastline to the front associated with the Jet has been found. This angle that has been estimated from the low passed time series of current velocity measured by the uppermost instrument of the moored line has been then used to identify the onshore–offshore excursions of the Jet. Both upwelling mechanisms are identified from hydrographic data, because each of them has associated a different type of water mass, and they take place in different locations. Wind-driven upwelling dominates in coastal zones, on the shelf, while upwelling associated with southward drifting of the AJ prevails further offshore. The amount of sub-surface water brought up to the surface by each one is of the same order. However, wind-driven upwelling contributes to the fertilization of this region in a major extent because water upwelled by wind is richer in nutrient concentration.     

Applying Human Systems Integration to the Rapid Acquisition Process

The rapidly changing complexity of the Global War on Terrorism has changed the approach to equipping forward-deployed military forces. Combatant Commanders conducting operations now require timely materiel solutions to enhance mission capabilities and reduce the risk for individual soldiers. To address this challenge, the US Army established the Rapid Equipping Force to assess emerging requirements, to propose solutions to those requirements, and to implement those solutions in an expedient time frame. Unfortunately, the REF lacks a consistent analytical methodology for assessing alternative materiel solutions. To address the need for a human systems integration (HSI) analysis method, the authors developed an Assessment-Based Rapid Acquisition HSI Analysis Method (ABRAHAM) capable of generating tailored surveys and evaluating these surveys for unacceptable risks to soldiers. To validate ABRAHAM's concept and content, ABRAHAM was showcased in three Department of Defense settings: the Human Factors Engineering Technical Advisory Group, the REF, and the US Marine Corps' Operational Test and Evaluation Activity. The ABRAHAM appears to fill a gap in the current library of HSI tools. Based on the feedback provided during the product showcases, there is sufficient interest and technological maturity to further develop ABRAHAM to serve both the traditional and rapid acquisition processes.     

Agricultural vehicles and sustainable safe road traffic: solving conflicts on arterial highways

Addressing the issues of traffic safety in rural areas presents a constant challenge. The mix of light and heavy vehicles and the considerable differences in speed among these traffic participants result in high risks and delays for the faster vehicles. Agricultural vehicles (AVs) in particular have such an impact on traffic, especially when using arterial highways. This paper reviews the problems of safety and delays that AVs cause on arterial highways, and the appropriate mitigation. The concept of 'sustainable safety' in The Netherlands focuses on these problems, because of the proposed construction of parallel roads alongside all arterial highways. However, Dutch accident statistics cannot justify the high costs for the construction of parallel roads alongside 7000 km of arterial highways. Delays experienced by fast traffic are another reason for separating AVs from other road users with parallel roads. Alternative measures alongside the arterial highway, such as passing bays, restricting AVs to travelling at off-peak only and improving the conspicuity of the AVs, may be more cost-effective ways of reducing delays and/or improving traffic safety on arterial highways. Another solution may be to eliminate the need for AVs to use the arterial highway by altering their routes. For this purpose, land reallocation projects (as practised in Holland) can provide a useful tool.     

National policy towards cars: Greece

Passenger car ownership and use in Greece has been a matter of serious consideration at government level, only in the last decade with the increasing traffic congestion in the big cities. However, government policy towards private car ownership has always been influenced by two main factors.

First, that virtually all vehicles have to be imported, a fact which has a serious balance of payments implication for a small country like Greece.

Second, the traditional heavy taxation of motor vehicles and fuel, brings high revenues for the national budget. Recently a third consideration has been added, that of energy consumption and of the environmental effects of car use.

From the point of view of car owners, ownership was originally seen as a means of social recognition and establishment, but for the last decade it has been considered mainly as an everyday necessity more or less imposed on one, by a number of other well accepted facts of everyday social and professional life.

Influenced by the two main factors above; private car ownership and use in Greece has developed for the last two decades at a pace similar to but not the same as in other Western Countries. In this paper the existing situation and prospects will be examined and comments made on the peculiarities characterizing the Greek scene.     

The authors in this issue

This paper analyses the impacts on a particular region of a recent policy change regarding public transit subsidy in New Zealand, under which the contributions of local authorities are increased from 0 to 50% of net direct expenditures. The options open to the community are examined and their effects on regional income, future development and social equitability are analysed. It also illustrates the cost effectiveness of a natural monopoly under increased accountability.     

Deregulating the bus industry in Britain: a rejoinder

In our critique for the Buses White Paper, we argued that ‘competition for licences’ could achieve most of the benefits of competition without the major disadvantages of ‘competition on the road’. In response to the comments of Beesley and Glaister, we explain how comprehensive franchising of good and bad routes alike would encourage effective competition, whilst providing conditions for the transparent continuation of cross‐subsidy where that was the choice of the local authority in question. We correct their misrepresentation of our arguments on the desirability of cross‐subsidy and on the case for minibuses, and explain why we believe that such cost savings as are achieved will be mainly at the expense of staff or customer service. Finally, we restate the case for believing that a unified planned timetable will provide a better service for a given level of resources than will uncoordinated competitive services.     

Changing patterns of urban travel Part 2. public transport and future patterns of travel

This two‐part paper contains most of a report prepared by TRRL for the European Conference of Ministers of Transport, and presented by one of the authors to the Council of Ministers in November 1984. Part 1, which was published in the January‐March 1986 issue of Transport Reviews, looked at the way cities have been changing over the years and the influence of growing car ownership on trip patterns. This part examines the changes in public transport use in more detail, considers the interactions between the various underlying trends, speculates on future travel patterns by both public and private means and considers the likely impact of land use and transport policies.     

Economic appraisal of European transport projects: The state-of-the-art revisited

Substantial investment has been made at national and European level in transport infrastructure over the past 50 years and is likely to continue in the future. The need to appraise transport projects in economic and social terms has developed alongside this in both scope and complexity. The state-of-the-art in the economic appraisal of transport projects is reviewed, progress is assessed and future challenges are identified. The review addresses the general framework, treatment of major impacts, presentation of outputs and issues such as uncertainty. It draws on national practice in Western European countries, which varies substantially reflecting a range of cultural and economic differences. Some points of commonality exist and the principle of monetizing direct transport impacts is generally accepted. Progress has been made towards the measurement of environmental impacts, but the assessment of the wider impacts remains under-developed. Increased sophistication and complexity has brought increasing data and presentation requirements, where computerized decision support methods have potential. Many challenges exist for the future of appraisal and the review is concluded with a discussion of some key issues. At the heart of these is the continuing debate over the relative roles of national and European government in decision-making and resource allocation.