Schedule Compression and Time-Cost Trade-Off - Construction Project Scheduling and Control - page 229

Cost $

CC

Accelerating

NC

LC

CD LCD ND Duration (days)

Figure 8.8 Effect of project acceleration on total cost: the general case, in which total cost
decreases with acceleration until a certain point and then starts increasing—CC, crash cost;
NC, normal cost; LC, least cost; CD, crash duration; LCD, least-cost duration; ND, normal
duration
increases at an increasing rate, until we either reach our desired duration/end date or
stop at the absolutely least possible duration, called crash duration (CD) , which has
an associated crash cost (CC) .
As mentioned previously, the shape and slope of the curve differ from one case
to another. In some cases, the curve may start going up immediately (i.e., total cost
starts increasing as soon as we start accelerating), as shown in Figure 8.9.
In other cases, the curve goes down and then stops at the crash duration point,
without going up anymore (see Figure 8.10). In this case, the crash duration point
coincides with the least-cost duration point.

Issues to Be Considered When Accelerating a Project

Accelerating a project affects many aspects in the project other than time. Failing to
consider these aspects may lead to undesired adverse results. The project manager
must consider issues such as the following:

Figure 8.9 Effect of project acceleration on total cost: a special case, in which total cost
starts increasing as soon as acceleration starts—CC, crash cost; NC, normal cost; CD, crash
duration; ; ND, normal duration. Least cost duration, LCD, coincides here with normal
duration, ND