Critical path method (CPM)
CPM is a project scheduling method where activities are arranged based on interrelationships and the longest time path through the network called the critical path is determined.
The critical path method focuses the relationship between the critical activities. It is an activity relationship representation of the project. Critical tasks which control the project duration are determined. Because of the size and complexity of major construction projects, the CPM is most often applied using a computer software program.
The CPM calls attention to which activities must be completed before other activities can begin.
CPM calculation define a time window within which an activity can be performed without delaying the project.
Requirements of Using CPM
Using the CPM to develop a schedule requires detailed investigation into all identifiable tasks that makeup a project. This means that manager must visualize the project from start to finish, and must estimate time and resource requirements of each task. It is good practice to also obtain information from superintendents and sub-contractors.
CPM Logic Network of Logic Diagram
The most important feature of the CPM is the logic diagram.
- The logic diagram graphically portrays the relationship between project activities.
- With this, it is easier to plan, schedule, and control the project.
- Reduces the risk of overlooking essential tasks and provide a blueprint for long-range planning and coordination of the project.
- Generates information about the project so that the manager can make timely decisions if complications develop during the progression of work.
- Enable the manager to easily determine what resources are needed to accomplish the project.
- Allows the manager to determine what additional resources will be needed if the project must be completed earlier than originally planned.
Critical path and critical activities
The critical path through a schedule network is the longest time duration path through the network.
It establishes the minimum overall project time duration. All activities on the critical path are critical activities. A critical activity may be determined by applying either of following rules :
- the early start and the late start times for a particular activity are the same.
- the early finish and late finish times for a particular activity are the same.