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At roundabouts where entering traffic is required to give way to traffic circulating in the roundabout, the traffic capacity of each entry is a function of the flow of traffic circulating past it. This relationship has previously been analysed in two main ways: using a linear relationship based on regression and using a non-linear relationship based on a model of entering drivers' acceptance of gaps in the circulating traffic. The linear analysis has previously been extended to estimation of the reserve capacity or degree of overload of the roundabout as a whole in relation to a given pattern of approaching traffic. The non-linear analysis is extended similarly in this paper.

The relationships between entry capacity and circulating flow imply in turn that the capacity of each entry is a function of the entering flows and the proportions of traffic making various movements through the junction from some or all of the entries. Equations are established for determining derivatives of capacity or delay on each entry with respect to the demand flow for each movement. In particular, it is shown that when the roundabout is overloaded the capacity of an entry can depend upon the demand flow on that same entry, giving rise to a corresponding term in the derivative of the delay-flow relationship for the approach concerned.

Purpose – Measures aimed at reducing intersection crashes have high potential to be cost effective since intersections constitute only a small part of the overall highway system but intersection-related crashes constitute more than 50% of all crashes in urban areas and over 30% in rural areas. Roundabouts are a proven safety countermeasure, but several issues that significantly affect both crash frequency and severity have been observed at both existing and new roundabouts. This chapter aims to provide guidance on roundabout selection and design criteria.

Methodology – The chapter first describes the most relevant criteria to be considered for choosing a roundabout. Then, after the explanation of the roundabout design process and a clear description of the roundabout classification, the chapter provides recommendations for all the steps of the geometric design, highlighting the main design features that contribute to the best safety performances, including speed control and sight distance checks. Finally, the chapter explains traffic control devices and facilities for pedestrians and cyclists.

Findings – Roundabout design needs to balance opposing demands and it is important to adopt a performance-based design approach within an iterative process. The most important performance check is the analysis of vehicle speeds through the roundabout, since achieving appropriate vehicular speeds has a very positive safety effect.

This conceptual paper examines and evaluates patronage and clientage as a system of interrelated dyadic exchanges between unequals through which goods and services circulate, flowing both up and down through stratified societies. The parties involved may be in different places socially and geographically.

Data are presented for Brazil from the period of the Old Republic beginning in the 1890s, through the end of the Military Dictatorship in mid-1980s, and finally to the present, ending with today’s conditional cash transfer programs. The data are examined against the background of a 15th century book, O Livro da Virtuosa Bemfeituria (The Book of the Virtuous Benefits), written by a Portuguese Prince influential in the expansion and discoveries as a guide for princes and great lords that is used in the paper very much in the way that Adam Smith’s writings are used for most economic behavior today.

There are striking parallels over this long historical period in the behaviors referred to as patronage and clientage that may be conceptualized as an older (traditional) way of ordering the flow of goods and services (distributing them), alternative and parallel to market mechanisms that have, and continue to operate in Brazilian society.

Patronage and clientage are often-misunderstood behaviors, sometimes referred to as corrupt, that alternatively may be explained and understood as part of a still viable and operational socio-cultural system that goes back to a period before the colonization of Brazil.