Critical path method

Critical Path Method or CPM is an important project management method that helps to schedule project activities and estimate project duration. CPM provides project manager with the below information:

• critical path for project completion,
• minimum time required to finish the project,
• dependencies between the tasks,
• time buffer,
• project timeline.

Critical Path Method was developed after World War 2 to schedule and manage complex construction and engineering projects. The method represented a network, where a set of events or activities were connected to each other in a flow manner leading from the beginning to the end. The intention was to represent the sequence of activities and relationships between them. At the same time, another method was developed, which is now closely associated with the CPM - Program evaluation and review technique (PERT). PERT was focusing more on the time that is required to complete an event or activity. As time passed, PERT was largely used together with CPM in project management (Fondahl J. W., 1987).

Critical Path Method

When a project enters planning phase project scheduling is taking place. For project scheduling project manager plans activities that will be completed as part of project execution. As part of this task, one must estimate the time that will be spent on each activity, budget, materials and labor. One of the methods that is used by project managers for project scheudling is Critical Path Method (Atin S., Lubis R., 2019). Critical Path Method is a very powerful method that provides information on what activities are critical for the project completion, what is the shortest possible project time and how best to schedule work to meet the desired results (Mercier A. G., 1965).

Nowadays, many computer programs offer CPM charts based on user characteristics, but the logic of the tool is almost the same for all of them. The project manager lists all tasks that must be completed as part of the project scope, their relationships and time estimates. Each activity or task is given a unique identifier, such as a letter or a number. Each activity is being plotted on the chart in circles and relationships are being established based on the data provided by the project manager. The sequence of relationships is being shown by arrows that are connecting two circles. There is a “start” circle, which links all activities that have no predecessors and there is a “finish” circle for activities that have no successor. A critical path is defined as the longest path in time from start to finish circles. This path indicates the minimum time required to finish the project and all its activities (Yang J-B., Kao C-K., 2012).

Fig. 1 Critical Path Method (source: Nikita Shtemenko)

The benefits of using the Critical Path Method are that the project manager can build a clear and cohesive schedule of the project. As part of this schedule, it is possible to see the information about latest start and latest finish, which also allows the project manager to plan their work and understand the time buffer that is available. Such time buffers can later be used for ad-hoc activities or to prevent the risk of delays (Zareei S., 2018).

Modern computerised technologies even allow project managers to apply budget on their critical path chart. This allows the project manager to view at which point in the project which costs will occur. Such information enables project managers to better budget management and mitigates the risks of cash gap or cash deficiency.

Critical Path Method should be used to determine the critical path of the project, to estimate the timeline of the project and dependencies of tasks. When using Critical Path Method, project manager should list all activites that are in scope of the project with the time required to finsih them. Then using specialised software, project manager will be able to convert list of tasks with time estimates to Gantt chart. Later a critical path method can be identified based on the Gantt chart.

The summary of the Critical Path Method

Below if the quick summary of the Critical Path Method:

1. Critical Path Method is a very common method that is used by many project managers to estimate the duration of the project, dependencies of the tasks and critical activities. CPM is often used together with the Gantt chart in project planning.
2. Critical Path Method was developed in the late 1950s in the United States for complex construction projects.
3. Critical Path Method is presented as a chart with a sequence of events from start to finish that represent their dependencies via arrows.
4. The technology is constantly evolving enabling project managers to apply budget, resources and time estimates on their chart for better coordination and management.

References

• Atin S., Lubis R. (2019), Implementation of Critical Path Method in Project Planning and Scheduling.IOP Conference Series Materials Science and Engineering 662(2).
• Fondahl J. W. (1987), The history of modern project management. Precedence diagramming methods: origins and early development. Project Management Journal, 18(2), 33–36.
• Mercier A. G. (1965), The Critical Path Method: its fundamentals. Monterey, California: U.S. Naval Postgraduate School.
• Yang J-B., Kao C-K. (2012), Critical path effect based delay analysis method for construction projects. International Journal of Project Management 30, 385–397.
• Zareei S. (2018), Project scheduling for constructing biogas plant using critical path method. Renewable and Sustainable Energy Reviews 81, 756–759.

Author: Nikita Shtemenko