The critical path method (CPM) is a project modeling and scheduling technique for large or complex projects. It was developed in the 1950s by analysts at DuPont and Remington Rand, influenced by work on the Manhattan Project (WW II research effort resulting in the introduction of nuclear weapons).
A core benefit of CPM is that it helps project managers stay on task and under budget by identifying individual tasks and their interrelated dependencies. Understanding these dependencies helps identify the anticipated time to begin and complete each task within the project. This effectively allows accurate schedule prediction when projects are comprised of hundreds of tasks.
The method gets its name from identifying the critical path: the longest stretch of tasks with interrelated dependencies. Simply put, the critical path is the sequence of related tasks that take the longest time to complete.
CPM analysis also generates a graphical display of that schedule, showing the total elapsed time, the critical tasks, and those interrelated dependencies. Many tasks in a project may not contribute to the critical path, yet they can also be illustrated in conjunction with it.
CPM is a reliable way for project managers to budget time and allocate resources.
In addition, other advantages of CPM include the following:
- Improved accuracy and flexibility in scheduling.
- Clearer communication between project managers and stakeholders.
- Easier task prioritization.
- Identification of which activities can run in parallel.
- Use of a practical and disciplined methodology to determine how to reach objectives.
- Strengthening a team’s collaboration toward shared goals.
- A straightforward process for documenting project details.
- Determination of slack time (or “float”), the measure of how long a given task can be delayed before it affects the project outcome.
- A clear method of communicating project plans, schedules, time, and cost performance.
Let’s dig into a few of the advantages…
Better communication: Using CPM to create schedules requires input from key stakeholders and participants throughout the project lifecycle. This means soliciting expertise from team members, subcontractors, and anyone else involved in the project, and it leads to a more realistic schedule from the beginning of the project.
Improved risk detection: CPM can prevent surprises and identify earlier opportunities for correction. Knowing the relationships between tasks can help project managers better predict the adverse effects of a delay in any task.
Easier prioritization: When CPM helps project managers determine the float for each task, it also helps them prioritize. Tasks with zero (or very low) float must remain a higher priority, while those with a larger float are non-critical in maintaining the schedule.
Improved visual representation: In this case, a picture really is worth a thousand words. A CPM network diagram provides a quick understanding of the project’s timeline and progress. It can also more easily highlight alternatives when schedule adjustments need to be considered.
More adaptability: CPM visual representations can provide managers with tools to rapidly rework or adjust schedules when something doesn’t go as planned.
Budget and cost control: By design, CPM is a methodology designed to prevent project delays. Delays often represent the most significant source of cost overruns in large projects. When project budget and expenditures are associated with sub-tasks (rather than the entire project), it can be easier to identify spending issues and adjust to stay within budget.
Thanks to these advantages, we expect CPM to continue being widely used.
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