The reliability based method presented in this paper is a very general way of treating uncertainty in many civil engineering problems and appears to be very convenient for road safety problems. Engineers are frequently required to forecast the future behaviour of a system. If the problem can be phrased as a demand for and a supply of a unique measure and if that measure can be placed in a closed form mathematical solution, and if the variables in the equation have known Pearson type distribution, and non-compliance or failure is due to random events, then the reliability methods given in this paper can be employed. Using the ideas of load factors in the demand function, a performance factor for the supply function and an accepted level of non-performance as given by the Reliability Index, the engineer-designer-analyst is forced to explore more thoroughly the interaction of demand-supply-success. The same results may be obtained by scenario based calculations or simulations but the reliability based techniques are computationally more efficient.
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