Allocating Resources

Once you have decided on the critical path for an activity network you will need to allocate resources to each task.

Resources could take the form of equipment, people, money, or any number of other things. Most often we will use people. The question you need to ask yourself is “how many people do I need so that the project can be finished without any delay?” In answering this question you are halfway to allocating resources.

In the example we have been looking at, there are at most three things that can be happening at any one time. Do we need to use three people, or will two people be enough (have we got enough time to complete H and I before G is completed)? Looking at the activity network we can see that there will not be enough time to do this.

Figure 1: Earliest and latest times for the house building activity network.

Another way of showing the resources needed is to draw a cascade chart and then a resource histogram.

The cascade chart in figure 2 shows the critical path on the lower row and has a row for each of the other activities, starting at their earliest time and showing float at the end. This allows the viewer to see where activities can be collapsed down to be allocated to a single worker. The collapsed form, as a resource histogram, is shown in figure 3.

Figure 2: Cascade chart showing the activities in the house building example. Critical path is the lower row.
Figure 3: Resource histogram for the house building example. A total of 3 workers are needed.