David Jarrett

ACCIDENT PREDICTION MODELS FOR ROADS WITH MINOR JUNCTIONS

The purpose of this study was to develop and validate a method for predicting expected accidents on main roads with minor junctions where traffic counts on the minor approaches are not available. The study was based on data for some 3800 km of highway in the U.K. including more than 5000 minor junctions. The highways consisted of both single and dual-carriageway roads in urban and rural areas. Generalized linear modelling was used to develop regression estimates of expected accidents for six highway categories and an empirical Bayes procedure was used to improve these estimates by combining them with accident counts. Accidents on highway sections were shown to be a non-linear function of exposure and minor junction frequency. For the purposes of estimating expected accidents, while the regression model estimates were shown to be preferable to accident counts, the best results were obtained using the empirical Bayes method. The latter was the only method that produced unbiased estimates of expected accidents for high-risk sites.

STABILITY ANALYSIS OF THE CLASSICAL CAR-FOLLOWING MODEL

This paper investigates the stability of the classical car-following model (for example, Chandler et al., Operations Research, 6, 165-184, 1958; Herman et al., Operations Research, 7, 86-106, 1959; Wilhelm and Schmidt, Transportation Engineering Journal (ASCE) 99, 923-933, 1973). Conditions for local and asymptotic stability as defined in the references cited are established for the linear model. These differ from those in the literature in two ways. First, it will be shown that, in the autonomous model when the product of the coefficient of proportionality [alpha] and the reaction time [tau] is less than or equal to 1/e, there exist oscillatory solutions with higher frequencies than 2[pi], although there are none with lower frequencies. Secondly, asymptotic stability is considered along with local stability. The derived condition for asymptotic stability is both necessary and sufficient. In addition, the condition depends on the frequency of the forcing term, with the sufficient condition [alpha][tau]

Market Segmentation and Product Differentiation in Political Campaigns: A Technical Feature Perspective

The perceived importance of five technical service qualities (Gronroos 1984) or features (i.e. national and local policies, leaders, values and candidates), and voters’ ratings of the Labour and Conservative Parties’ competence on each of these parameters, were investigated during the 2001 British General Election using an a priori segmentation method and the classification tree statistical technique for data analysis. Voter ratings of the technical service features were found to be indicators of intention to vote. A product differentiation approach is most likely to influence voting intention, because the technical service features are more readily manipulated through marketing programmes than demographic and customer characteristics (Bucklin and Gupta 1992). Ratings of technical service features are stronger indicators of voting intention than voter demographics and characteristics. A product differentiation approach, based around technical service features, would be the most effective focus for strategy development in future political marketing campaigns.

Dose–response functions for the soiling of heritage materials due to air pollution exposure

A set of materials (Portland limestone, white painted steel, white plastic and polycarbonate filter material) was exposed at locations in London, Athens and Krakow. Regular measurements of reflectance were taken over a period of twelve months. Co-located measurements of PM(10) concentrations were available. Based on these results, the relationship between soiling (measured as loss of reflectance) and ambient PM(10) concentrations was quantified leading to the development of dose-response functions for the soiling of materials. The results for limestone revealed too much scatter for a prediction to be made. Implications for air quality management and for the conservation of cultural heritage buildings are considered, including public acceptability and economic factors.

Chaos in a dynamic model of traffic flows in an origin-destination network

In this paper we investigate the dynamic behavior of road traffic flows in an area represented by an origin-destination (O-D) network. Probably the most widely used model for estimating the distribution of O-D flows is the gravity model, [J. de D. Ortuzar and L. G. Willumsen, Modelling Transport (Wiley, New York, 1990)] which originated from an analogy with Newtons gravitational law. The conventional gravity model, however, is static. The investigation in this paper is based on a dynamic version of the gravity model proposed by Dendrinos and Sonis by modifying the conventional gravity model [D. S. Dendrinos and M. Sonis, Chaos and Social-Spatial Dynamics (Springer-Verlag, Berlin, 1990)]. The dynamic model describes the variations of O-D flows over discrete-time periods, such as each day, each week, and so on. It is shown that when the dimension of the system is one or two, the O-D flow pattern either approaches an equilibrium or oscillates. When the dimension is higher, the behavior found in the model includes equilibria, oscillations, periodic doubling, and chaos. Chaotic attractors are characterized by (positive) Liapunov exponents and fractal dimensions.(c) 1998 American Institute of Physics.

Product Attribute-Based Voter Segmentation and Resource Advantage Theory

Political parties have long since targeted the marginal constituency and floating voters using demographic segmentation approaches and the use of market segmentation techniques in general election campaigns is now well-documented (see Johnson 1971; Ahmed and Jackson 1979; Yorke and Meehan 1986; Baines et al. 2003). The actual practice of segmentation as undertaken by political parties and its relation to theory is less well-considered. This paper represents a serious attempt to outline how political parties targeted a priori segments of the electorate including gender, age and lifecycle in the 2005 British General Election when they should have been adopting a product attributed-based approach. Selected MORI surveys from April 2005 were analysed, using logistic regression to indicate the most important factors in determining how Britons vote. Principal components analysis provides an indication of how the three main British political parties are perceived. The paper discusses, using resource-advantage theory (Hunt 1995; Hunt and Arnett 2004) how political parties might use their party and leader image, and policies to build their popularity in an election campaign.

CONFLICT-MINIMISING TRAFFIC PATTERNS: A GRAPH-THEORETIC APPROACH TO EFFICIENT TRAFFIC CIRCULATION IN URBAN AREAS

Abstract The paths followed by vehicles in urban areas are densely interwoven, and some of the accidents and congestion that occur in city centres can be attributed to the ‘conflicts’ that arise where these paths intersect. Hence, it is desirable to encourage traffic patterns in which the frequency and severity of conflicts are minimised. At present, neither signal optimisation programs nor traffic simulation programs allow the user to experiment freely with different combinations of one-way streets and turn restrictions, which might otherwise help to disentangle conflicting movements. There is no accepted formula or philosophy for organising traffic into a coherent spatial pattern. The aim of this paper is to consider some idealised networks and circulation systems that have simple geometrical configurations, and to identify those systems that are relatively efficient in terms of path crossings, as compared with a theoretical yardstick derived from graph theory. The results provide some pointers towards a general strategy for efficient traffic circulation in urban areas.

SPATIAL ASPECTS OF TRAFFIC CIRCULATION: I. A REVIEW OF ALTERNATIVE SYSTEMS

One of the key aims of traffic management is to encourage drivers to follow an efficient routing pattern (i.e. a set of routes that collectively minimise the potential for delays and accidents and possibly also minimise travel distance). At present, little is known about the relative merits of different patterns or how they could be accommodated or encouraged within existing city centre networks. A number of archetypes are compared using total vehicle conflicts and total travel distance as the main criteria. They include several that have not previously appeared in the literature, and, the conflicts are weighted to reflect variations in the severity of the interactions between vehicles carrying out different turning movements at junctions. The results indicate wide variations in the characteristics of different routing patterns and suggest new ways of organising the spatial pattern of traffic circulation as possible alternatives to the conventional gyratory system.

Spatial distribution of road crashes in Great Britain

Abstract Please click here to download the map associated with this article. Road crashes are a major cause of death and injury worldwide. Sophisticated statistical methods are needed to study their distribution and to evaluate the effectiveness of road-safety policies and measures. This paper shows how maps can be used to study the spatial distribution of crashes, to identify data errors, and to plot the results of statistical modelling.

Spatial aspects of traffic circulation: II. Routing patterns that exactly minimise path crossings

The total number of path crossings between vehicles following different routes on a road network can be taken as a rough proxy for congestion and accident risk. It is therefore useful to identify ways of routing traffic in the plane such that the numbers of crossings are minimised; these can serve as models for the design of traffic management schemes in urban areas. The authors have previously investigated a number of routing patterns; the best ones generated path crossings whose number exceeded a conjectured minimum by 33%. In this article, two configurations are put forward that achieve the minimum value. The networks required to support such routing patterns are probably not realisable in practice, but the exercise provides a useful insight into the traffic circulation problem and suggests a yardstick against which other routing patterns can be evaluated.