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CRITICAL PATH

The Critical Path Method, abbreviated CPM, is a mathematically based algorithm for scheduling a set of project activities. It is a very important tool for effective project management. It was developed in the 1950's in a joint venture between DuPont Corporation and Remington Rand Corporation for managing plant maintenance projects. Today, it is commonly used with all forms of projects, including construction, software development, research projects, product development, engineering, plant maintenance, among others. Any project with interdependent activities can apply this method of scheduling.

The essential technique for using CPM is to construct a model of the project that includes the following:

  1. A list of all activities required to complete the project,
  2. The time (duration) that each activity will take to completion, and
  3. The dependencies between the activities.

Using these values, CPM calculates the starting and ending times for each activity, determines which activities are critical to the completion of a project (called the critical path), and reveals those activities with "float time" (are less critical). In project management, a critical path is the sequence of project network activities with the longest overall duration, determining the shortest time possible to complete the project. Any delay of an activity on the critical path directly impacts the planned project completion date (i.e. there is no float on the critical path). A project can have several, parallel critical paths. An additional parallel path through the network with the total durations shorter than the critical path is called a sub-critical or non-critical path.

These results allow managers to prioritize activities for the effective management of project completion. Originally, the critical path method considered only logical dependencies among terminal elements. Since then, it has been expanded to allow for the inclusion of resources related to each activity. This capability allows for the exploration of a related concept called the critical chain, that determine project duration based upon both time and resource dependencies.

Since projects schedules change on a regular basis, CPM allows continuous monitoring of the schedule, allows the project manager to track the critical activities, and ensures that non-critical activities do not interfere with the critical ones. In addition, the method can easily incorporate the concepts of stochastic predictions, using the Program Evaluation and Review Technique (PERT).

Currently, there are several software solutions available in industry today that use the CPM method of scheduling, see list of project management software. However, the method was developed and used (for decades) without the aid of computers (with pencil and paper).


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