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A Guide to the Critical Path Method

Project managers looking to avoid getting bogged down in process holdups can apply the critical path method, a project management technique that distinguishes critical tasks from non-critical tasks.

Particularly useful for projects comprised of abundant, complex and interrelated tasks, the critical path method (CPM) models the total project, looking for the quickest, and least resistant, path to completion at each stage. This model lists all necessary tasks, maps how tasks are connected and estimates how long each task will take to complete. With this bird’s-eye view, the project manager can spot critical paths that could extend the project timeline, as well as tasks that are more flexible.

The History of the Critical Path Method

The Critical Path Method originated in the Manhattan Project of the 1940s, when scientists and managers identified critical tasks to the project and estimated the total project timeline, according to Workamajig. The large defense and technology projects of the 1950s further established CPM as a routine approach to project task and timeline planning.

In 1978, Dr. Larry Bennett, a civil engineer and project manager, authored  “Critical Path Precedence Networks,” a guide on the critical path. The CPM technique, according to Bennett, provides a planned schedule and enables the project team to benchmark against that schedule.

Although it started with critical defense projects, today CPM has been adopted by many fields, including hardware and software development.

How the Critical Path Method Works

In a project, the “critical path” is the longest sequence of tasks required to complete the project. In other words, it is the absolute shortest amount of time the project can take because it is composed of the fundamentally critical steps that must be taken for the project to be successfully completed. How do project managers identify this path? First, they identify the networks, or dependent tasks, within the projects. Assuming they have every resource necessary, they calculate the earliest possible start and finish, as well as the latest start and finish, in what the PMBOK® Guide – Sixth Edition calls a “forward and backward pass analysis of the schedule network.”

In simple terms, this can be likened to making a pizza. Some steps a cook will take are critical for the final product to actually be a pizza: Preheat the oven, let the dough rise, roll out the dough, add tomato sauce, grate and add cheese, cook the pizza. Other steps, like chopping and adding peppers, rolling cheese inside the crust or preparing seasonings are not critical, and therefore not part of the critical path. If the cook doesn’t chop and add peppers, the end product will still be a pizza. But if the cook doesn’t put the raw pizza in the oven, the product will not be an edible one.

As part of a full understanding of the critical path, project managers will also need to review additional areas, including:

Float or Slack: These interchangeable terms refer to how much time a project task could delay without delaying the overall project timeline. This would not include tasks on the critical path. In the pizza example, the non-critical task of chopping peppers can occur at multiple times: while the dough is rising, while the oven is preheating, or perhaps even for a few minutes when the pizza is first cooking. Mapping out the float is critical to managing resources well, as it allows project managers to determine which tasks can be delayed to better use resources.

Resource Constraints: Project managers must also assess resource constraints to correctly establish the critical path. The original mapping exercise looks only at dependencies among tasks, but Task A and Task B can only be completed in tandem if there are two resources to do this. If these interdependent tasks are on the critical path and resources are not available to complete both tasks at once, the critical path will need to be adjusted. 

Benefits of the Critical Path Method

Project managers using the critical path method must consider multiple factors that could impact the timing, as well as plan for both the shortest and longest outcomes. When critical path mapping is complete, project managers have a visual representation of all project tasks. This approach yields several benefits:

Establishes the most important tasks: This fact-based assessment points project managers directly to the most central project tasks, allowing them to focus carefully on these critical aspects.

May reduce timelines: When project managers have a clear view of which tasks will most directly impact timelines, they can better control those aspects, avoiding adjusting any tasks that can directly influence the timeline.

Provides timing benchmarks: Throughout the project lifecycle, project managers can benchmark the actual progress of the project against the planned timing, maintaining a current, visual schedule for the project.

Optimize efficiency: By clearly establishing how tasks relate to one another (or depend on one another), project managers can maximize the project team’s efficiency, scheduling tasks to occur without delays, or be conducted in tandem when that is possible and resources allow.

With careful upfront planning and consideration, the Critical Path Method can equip project managers to better understand and manage timelines, plan for potential pitfalls and maximize their team’s efficiency.

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