What is the Critical Path Method (CPM) in Project Management?
The critical path method (CPM) is a fundamental concept in project planning and management. It is a useful technique used for scheduling project activities like PERT method. The critical path of a schedule demonstrates the activities that can not be delayed. Because any delay in the critical path causes the delay of the project. In other words, in order to complete the project on time, activities on the critical path must be completed on time. This article discusses the Advantages and Disadvantages of the Critical Path Method and analyzes the steps for better understanding.
A Brief History
The critical path method was developed by James E. Kelley and Morgan R. Walker as a scheduling technique in the 1950s. It was developed for the US Navy Polaris Missile Program like the PERT method. Although both techniques serve the same purpose, they use different methods to calculate the activity duration. Gantt charts which did not involve activity relationships were in use before the development of critical path and PERT methods. Since it was developed in the DuPont Company in 1957, the critical path method has become an efficient tool for tracking the project schedule.
This method is widely used in today’s projects. It is applicable to all kinds of projects from various industries.
Critical Path Method Definition
The concept of the critical path method is discussed widely in the PMBOK Guide. Therefore it is an important concept for the PMP Exam. According to The Project Management Body of Knowledge (PMBOK), The Critical Path is “the sequence of scheduled activities that determines the duration of the project.”
Simply put, in this method, activities are listed, activity durations are determined, dependencies between the activities are established and the longest path is identified by making forward and backward calculations.
In a schedule network diagram, many paths can be seen starting from a point and ending at a point. These paths consist of activities which have durations and dependencies. Each path has some duration but the critical path is the longest path of the network diagram. In other words, it is the shortest time possible to complete the project
How is Critical Path Calculated?
Below steps are used for implementing the critical path method.
1. List the Activities
Activities can be determined by using the work breakdown structure and project scope. The scope of work defines the deliverables required to complete the project. The work breakdown structure divides the project scope into meaningful work packages.
2. Establish Dependencies
Activity dependencies represent the relationship between the activities. Predecessor and Successor activities should be determined in this step. Below questions should be answered;
Which activity will start before this activity ends?
Which activity will finish at the same time as this activity?
Which activity will start after this activity ends?
3. Draw the Network Diagram
After the identification of activities and establishing their dependencies, a network diagram can be drawn. Below figure illustrates a simple network diagram.
4. Estimate Activity Completion Time
Activity durations can be estimated by using past experiences, productivity analysis, and three-point estimation method.
Unlike the Critical Path Method, The PERT Method relies on three-point estimation. In three-point estimation, activity durations can be determined by making the estimations below;
– Most Likely Estimate: The most likely estimate
– Optimistic Estimate: The best-case estimate
– Pessimistic Estimate: The worst-case estimate
5. Identify the Critical Path
Forward and backward pass calculation is used to determine the critical path and total float. By the help of the Forward Pass and Backward Pass calculations, the earliest start and finish dates, and the latest start and finish dates for each activity can be identified and the Critical Path of the network diagram can be determined.
What are the Advantages of the Critical Path Method?
The following are a few benefits of the critical path method:
- It improves decision making within the project team
- It is a visual technique which enables to show activities, activity dependencies and durations in the same diagram
- It enables the project team to make time optimizations.
- It enables to manage and organize large and complex projects
- It enables to calculate The Earliest Start/Finish and The Latest Start/Finish dates in order to manage activities and procurement tasks.
- It helps to determine which activities can be delayed without delaying the project
- Schedule compression methods such as fast-tracking and crashing rely on the critical path method.
What are the Limitations of the Critical Path Method?
Below are the limitations of the Critical Path Method
- It is hard to manage activities in large and complex projects without software tools.
- It does not consider resource allocations.
- Activity durations should be determined correctly otherwise, the critical path of the project will be wrong.
- It will be hard to determine the critical path if there are many other similar duration paths in the project.
In this article, we discussed the advantages and disadvantages of the critical path method and analyzed the steps to provide a better understanding. Basically, the critical path method (CPM) is a strong tool in project time management. It is used widely for project planning and updating purposes by specialists. This method gives the project management teams correct completion dates for their projects. However, it is not easy to apply this method to large-scale projects that have thousands of activities without the support of software tools. Softwares like Primavera P6 and Microsoft Project can be used to determine the critical path of a project easily.
 Kelley, James; Walker, Morgan. Critical-Path Planning and Scheduling. 1959 Proceedings of the Eastern Joint Computer Conference.
Linda Maltz is vice president of design and consulting at Cuboca, a project management training and consulting organization specializing in construction management and BIM. She is certified Primavera P6 Trainer.