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- Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese
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- Volume 49, Issue 3, 2007
Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Volume 49, Issue 3, 2007
Volumes & issues
Volume 49, Issue 3, 2007
Forecasting household car ownership in South Africa : alternative models and future trends : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 2 –10 (2007)More Less
The paper investigates the use of an alternative household car ownership modelling approach for South African urban areas, particularly the metropolitan areas, that moves away from existing race-based classifications, but instead uses household income and spatial attributes of an area captured in terms of dwelling unit types. The model has been successfully calibrated for the City of Johannesburg, and tested for other Gauteng areas. The paper also provides limited benchmarking of South African household car ownership against published literature, in which it is illustrated and concluded that localised research on behavioural market responses is critical. Topical issues such as development density and lifestyle choices within the context of the emerging nature of household car ownership in South Africa are also investigated, although the transitional nature of the South African economy presents some analytical challenges. Finally, the paper illustrates the model's application in the urban development planning context. The model results, supported by other qualitative considerations, point to a potentially explosive growth in car ownership to be expected in historically disadvantaged areas of South African cities as middle-class incomes grow. Thematic areas for further research in the field are also identified.
Author Martin SlavikSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 11 –15 (2007)More Less
A method for the evaluation of accuracy of weigh-in-motion (WIM) scales based on Monte Carlo simulation is proposed. The objective of the method is to assist with decision on acceptance of the tested WIM scale as sufficiently accurate, or its rejection. Conceptually, the method considers a 'nebula' of possible populations that could supply the observed sample of n weighing errors. Excessive WIM weighing error is defined as an error falling outside a specified acceptance region. The percentage of excessive errors, Q, is then determined in each of the above populations. The distribution of Q is constructed and the probability of Q exceeding a tolerable limit Qcrit is determined from this distribution. Verdict on acceptance or rejection is formulated in terms of the above probability and displayed graphically. Also graphically displayed are risks of wrong acceptance and wrong rejection. This allows the user to make decisions with a full view of consequences. The method is simple to use and its applications indicate that, when using conventional WIM-accuracy testing procedures, one may under-estimate the risk of wrong decision. The objective of the paper is to introduce and explain the principle of a method for correct evaluation of accuracy of weigh-in-motion scales. The purpose of the method is to assist with decisions on acceptance of the tested scale as sufficiently accurate, or its rejection.
Analysis of water savings : a case study during the 2004 / 05 water restrictions in Cape Town : technical paperSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 16 –26 (2007)More Less
In October 2004 the City of Cape Town implemented water restrictions in line with the city's holistic approach to water demand management. To better understand the savings and improve the effectiveness of future restrictions, a detailed demand analysis was conducted during this period. In this paper the authors report on various aspects pertaining to the savings achieved. Emphasis is placed on the residential sector, but savings from other sectors are also presented. This is the first reported work in South Africa on the analysis of metered water demand and savings obtained in different consumer categories during water restrictions. Monthly metered consumption prior to and during water restrictions was recorded and analysed. The analysis shows that the water restrictions resulted in notable water savings in all administrative areas and for all land use, stand size and income categories included in the analysis. The residential sector is found to have a significant contribution to the total water saving. The paper explains the nature of these savings and also addresses the pitfalls and successes of the project.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 27 –32 (2007)More Less
Water distribution systems operate under constantly varying conditions that display both deterministic and probabilistic behaviour. Design guidelines, on the other hand, typically specify reservoir storage capacity in terms of deterministic parameters only. A method is presented for analysing the reliability of municipal storage reservoirs based on stochastic models of water demand, pipe failures and fire events. The method was applied to the Yeoville water supply system in Johannesburg and showed that its reservoir complex has a good level of reliability even though it is significantly smaller than required by the South African design guidelines. The analysis considered a number of layout changes to the supply network which could have significant impacts on the reservoir reliability. In conclusion, it is shown that the sporadic demands of fire flow do not significantly affect the reliability of the Yeoville reservoir complex.