ABSTRACT

The common feature of scheduling techniques described in previous chapters was the reliance on the deterministic expression of time. Deterministic scheduling is based on the use of average time estimates in determining duration of activities. The planner who is responsible for the development of a schedule commonly adds allowances for uncertainty into average estimates of time. Top management then assesses the degree of ‘uncertainty’ that surrounds the entire project and formulates a project contingency. This contingency too is added to the schedule. Thus a contingency for uncertainty is often added to a schedule twice, first by the planner and second by top management. A rather risky estimate of duration of activities expressed as an average, as alluded to in Chapter 11, is thus transformed into a less risky estimate. In most cases contingencies are determined arbitrarily, largely based on past experiences of planners. Formulating activity durations in this manner does not permit the planner to understand the degree of exposure of a construction schedule to risk.