English: Example of CPM Network Diagram

The critical path method (CPM) has proved a successful method for planning, organizing, and controlling projects. Initially, this management tool outlines the project graphically in the form of a network diagram. This representation, shown in Figure 12-3, illustrates:

• The required operational sequence,
• Which operations are concurrent, and
• Which must be completed before others can be initiated.

CPM operations are referred to as activities.

In Figure 12-3, an example of the application of CPM to the installation of a traffic control system, the activities necessary to complete the project are denoted by a line with an arrowhead. The circled numbers represent events which mark the beginning or completion of an activity. Dashed lines represent dummy activities which do not require any time but must be completed before another event can occur. The number below the activity represents the amount of time required to complete the activity. The critical path represents the project duration. In the example, the critical path is represented by the activities associated with events 1-11-15-19-23-27-29-31.

In the example, if activity 7-21 required a time of 10 instead of 8, then the critical path would become 7-21-23-27-29-31, because this sequence of activities would require a longer time. In this case, the receipt of mast arm poles would establish the critical path because they must be received before they can be set in place.