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A wideband feed network for a Vivaldi antenna array is presented. A limitation of current wideband antenna arrays is the bandwidth of either the feed network or the antenna element. The proposed antenna array consists of four wideband Vivaldi antennas fed with an improved wideband feed network to extend the useable bandwidth of the array. The proposed feed network consists of coplanar waveguide-to-slotline-to-microstrip line transitions. The feed network has a single coplanar waveguide input and four microstrip line output ports. The feed network achieved uniform amplitude and phase balance and an impedance bandwidth of 160% from 1 GHz to 9 GHz. The feed network was used in a uniform linear antenna array to feed four Vivaldi antenna elements. The Vivaldi antenna array achieved stable radiation patterns from 1.3 GHz to 8 GHz, resulting in a useable bandwidth of 144%. The antenna array has a minimum gain of 8 dBi and a maximum of 13.8 dBi within the frequency band. Results for a prototype Vivaldi antenna array, measured in a compact antenna test range, are presented and compared to simulated results from CST Studio Suite.

Data generated from telemetry devices, such as acceleration and speed, are used in a variety of industries to determine the risk profile of a driver. This paper considers the addition of road gradient as a contextual variable to a driving behavior model to determine specifically if the risk of a driver is influenced by different road grades. This behavioral risk is demonstrated by comparing the performance of heavy vehicle drivers with and without the addition of road grade as a variable. This is done by using accelerometer data of 48 heavy goods vehicles over an entire month, and appending elevation data from digital elevation model (DEM) data, specifically that of the Shuttle Radar Topography Mission (SRTM), to the vehicles’ GPS traces. The elevation values are used to calculate road grade values which are then categorized in five grade levels. The results show that there is a clear influence of gradient on the behavior of the drivers studied. There is also evidence that steeper sections on a road can cause a change in an individual’s performance when compared with the group.

ispartof: TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT vol:112 status: published

ispartof: COMPUTERS & OPERATIONS RESEARCH vol:146 status: published

Environmental Diversity (ED) has been proposed as a potential biodiversity surrogate for use in spatial biodiversity planning. The concept is based on the premise that differences in species composition between areas are correlated with differences in environmental conditions. If this is true then sites selected to represent the full range of environmental conditions in an area should provide good coverage of species diversity. This is potentially significant for conservation planning because environmental data are more easily available while species distribution data are often incomplete, but empirical tests of ED have been inconclusive. We explored the value of ED as a biodiversity surrogate using species distribution data from South Africa, focusing on how implementation affects its performance. We used empirical distribution datasets for birds, butterflies, frogs, and reptiles as well as artificial species distributions and modeled distributions for butterflies. Our results show that the form of the underlying optimization model and the number of environmental variables have a significant effect on the performance of ED while the choice of heuristic procedures for selecting sites has no significant effect. We conclude that ED can perform well as a biodiversity surrogacy strategy if it is implemented correctly.

As transport modellers we are interested in capturing the behaviour of freight vehicles that includes the locations at which vehicles perform their activities, the duration of activities, how often these locations are visited, and the sequence in which they are visited. With disaggregated freight behaviour data being scarce, transport modellers have identified vehicle tracking and fleet management companies as ideal third party sources for GPS travel data. GPS data does not provide us with behavioural information, but allows us to infer and extract behavioural knowledge using a variety of processing techniques. Many researchers remain sceptical as specific human intervention, referred to as ‘expert knowledge’, is often required during the processing phase: each GPS data set has unique characteristics and requires unique processing techniques and validation to extract the necessary behavioural information. Although much of the GPS data processing is automated through algorithms, human scrutiny is required to decide what algorithmic parameters as considered ‘best’, or at least ‘good’. In this paper we investigate the repeatability and reproducibility (R&R) of a method that entails variable human intervention in processing GPS data. More specifically, the judgement made by an observer with domain expertise on what clustering parameters applied to GPS data best identify the facilities where commercial vehicles perform their activities. By studying repeatability we want to answer the question ‘if the same expert analyses the GPS data more than once, how similar are the outcomes?’, and with reproducibility we want to answer the question ‘if different experts analyse the same GPS data, how similar are their outcomes?’ We follow two approaches to quantify the R&R and conclude in both cases that the measurement system is accurate. The use of GPS data and the associated expert judgements can hence be applied with confidence in freight transport models.

Paratransit provides a valuable service oering as a exible and substitutional mode between formal transit and private car. When it evolves to compete with more formal transit modes, eorts are made to formalise it. As in many developing countries, the South African government generally views paratransit as a necessary nuisance, emerging and evolving in the absence of more formal transit services. Our paper aims to contribute by providing a more comprehensive context for the South African case: how specic Apartheid laws contributed to the formation of the mode and how deregulation provided a fertile ground for its exponential growth. The industry has evolved into an informal yet well-organised system that dominates the local transit market. Contrary to the popular view that the industry is an amorphous whole, this paper aims to create a more peoplecentred view of an industry that is made up of individuals trying to carve an existence in a harsh economic environment. We show how, if approached correctly, paratransit is more likely part of the land use and transport solution, and not a problem as it is often perceived to be.

The paper describes the use of Global Positioning System (GPS) data obtained from commercial and project-specific sources to examine the travel behavior and fuel consumption patterns of drivers over a 3-day period in Gauteng Province, South Africa. Data for commercial (truck and light delivery vehicle) traffic were obtained from a commercial fleet management provider that continuously tracked the movements of 42,000 vehicles. Data for private car users came from a panel of 720 drivers, whose multiday driving activity was tracked by mobile passive GPS loggers. The driving behavior of the two driver populations was analyzed and compared in terms of the total distance traveled: spatial patterns (e.g., the amount of travel on different types of road) and temporal variations (e.g., variations between times of day and between multiple days). The detailed nature of the GPS data permitted the estimation of fuel consumption at a very disaggregate level (by link and time of day) and the identification of differences between user groups; these factors have significant implications for transport and energy policy. A new indicator, the recovery ratio, was introduced to assess the relationship between fuel use and distance traveled on different classes of road and to help identify equity distortions between user groups. The paper also discusses research needs related to the collection and integration of GPS data from multiple sources for model calibration and program evaluation.

We introduce complex network analysis and use a commercial vehicle’s observed trip as a proxy for a business relation between two facilities in its activity chain. We extract facility locations by applying density-based clustering to GPS data of commercial vehicle activities. The network among the facilities is then extracted by analysing the activity chains of more than 25,000 commercial vehicles. Centrality metrics prove useful and novel in identifying and locating key logistics players. Transport planners and decision makers can benefit from such an approach as it allows them to design more targeted initiatives and policy interventions.

To address the underreporting of freight from a transport geography point of view, we present a novel analysis of the time and spatial characteristics of disaggregated commercial vehicle activities. The activities were extracted from raw global positioning system (GPS) data collected in South Africa over a six-month period for more than 30,000 commercial vehicles. The analyses of the activity chains provide useful characteristics such as activity and chain durations, number of activities per chain, and the spatial extent of the activity chains. Key results indicate that about 60% of activity chains have between 5 and 15 activities per chain while 25% of the chains have 4 or less; 89% of the chains have a duration of 24 hours or less; and approximately 75% of all activities start between 08:00 and 17:00. The paper’s contribution is twofold: it firstly demonstrates a methodology to extract and evaluate vehicle activities and activity chains from raw GPS data. Novel results and characteristics about transport geographies in Gauteng, the economic centre of South Africa, are presented. We also report on the sensitivity of the analyses to certain parameters. Secondly, we introduce new metrics to evaluate a geographical area’s economic productivity based on commercial activity.

Management of a game ranch is an important issue as many game ranches operate on meagre profits, and some even at a loss, as their part-time owners subsidize the ranches from other sources of income. In this paper, we address the sustainable game ranching problem in a South African context through an optimization model. To obtain a faithful picture of reality, the model includes conflicting objective functions, and takes into account the fact that annual rainfall is known only stochastically. An approach for solving the resulting multiobjective integer linear stochastic program is discussed and illustrated by means of a numerical example from a Northern Cape ranch.

Maintenance analysis of an n-unit warm standby system with varying repair rate and the vacation period for the repair facility is studied in this paper. This vacation period occurs after each repair completion. Also, the repair rate of a unit depends on the number of failed units at the epoch of the commencement of the repair. The life time of a unit while on line is arbitrarily distributed random variable, while in standby has a constant failure rate. Identifying suitable regeneration points, expressions for the availability, reliability and the profit function are derived. A numerical example provided to illustrate the results obtained.

South Africa is nearly 20 years into its democracy, yet the legacy of apartheid remains evident and the level of inequality steadily rising. Gauteng province, the economic heart of the country that includes Johannesburg and Tshwane, the capital, carries the burden of many of its formerly relocated citizens still living in poverty on the periphery of the large metropolitan areas. Whereas sprawl is commonly associated with low-density, more affluent development on the periphery, Gauteng finds itself with having to provide basic services and mobility to high density, low-income people on its outskirts. The mobility culture in Gauteng is heavily influenced by the socioeconomic disparity. In this chapter we revisit the legislative context that gave rise to racial segregation, and concern ourselves with the impact it had in the evolution of the now-dominant paratransit mode that accounts for more than two thirds of all commuter trips in Gauteng. Although often cited in literature and the media for its violent sectarian conflicts, the minibus taxis, as it is commonly referred to, is much more than a mere mode of transport. Outsiders often perceive the taxi industry to be a chaotic system, but it has evolved into a powerful economic industry with a unique mobility culture, most notably the hand signals—a silent gestural semiotic language in its own right—used by commuters to communicate their desired destinations to passing taxis. Aware of the rising inequality, and not fully understanding or appreciating the exibility it provides, government often perceives paratransit as a necessary nuisance that should be formalised. Improving mobility and accessibility, however, requires both settlement location and transport to be revisited. As such, paratransit may prove to a valuable solution, and not the mere nuisance it is often made out to be.