Critical Path Vs Critical Chain Method (CPM Vs CCPM)

Critical path (CPM) and critical chain project management (CCPM) are popular frameworks for developing project schedules. Both frameworks allow you to develop a network diagram, find a critical path, and manage critical activities.

In today’s blog post, I will explain the critical path vs critical chain in detail so you can understand each scheduling technique and select the right framework for your project.

Let’s get started.

Critical Path Project Management (CPM)

The critical path method helps you manage projects by showing the critical activities. You can develop the critical path network diagram by listing all the tasks needed for the project. Then, decide how long each task will take, sequence them, and find their dependencies. Create a chart to show these tasks and their order.

Identify the path with the longest duration, which is called the critical path. This path shows the minimum time needed to finish the project. The whole project will be delayed if any task on this path is delayed.

CPM helps you focus on critical tasks and ensure everything is done on time. By knowing which tasks are on the critical path, you can prioritize your efforts and avoid delays.

Critical Chain Project Management (CCPM)

Critical chain project management is an updated version of the critical path method. It helps you manage projects by focusing on time and resources. This is similar to the critical path but considers resource constraints.

CCPM adds buffers, or extra time, to protect the project from delays. These buffers are placed at the end of the critical chain and other key points. They help absorb any delays in the tasks.

By using CCPM, you can handle changes and problems more effectively. You can focus on completing tasks on time while watching the buffers. This method helps ensure the project finishes on schedule, even if some tasks are delayed.

In the critical path method, you use float instead of buffer.

The differences between buffer and float are:

• Float or slack is a critical path phenomenon, while buffer belongs to the critical chain.
• Float is the difference between the duration of the critical and non-critical paths, and buffer is based on contingencies.
• Float is zero on a critical path, while buffer is not zero on a critical chain or any other chain.
• Float is the same for all activities on a non-critical path. Any activity can consume it partially or fully; others can use the balance. There is no further analysis.
• Any activity can also borrow a buffer if it is delayed. The project manager will analyze the remaining buffer to determine the project status.
• Buffers can be divided into project, feeding, and resource. Float is either total or free.

How to Create the Critical Chain Network Diagram

To create a critical chain network diagram, first, create a critical path network diagram. 

Then follow these three additional steps to develop a critical chain network diagram:

1. Remove all contingencies from activities. If you used a PERT (Program Evaluation and Review Technique) estimate to build the schedule, then replace the PERT estimate with an optimistic estimate.

2. Align the activities with late finish dates and remove resource constraints. Prioritize critical chain activities while assigning resources.

3. Add feeding buffers to non-critical chains so their durations equal the critical chain. Add the project buffer to the end of the critical chain but before the project end date. 

You can see that the critical chain method is a modified form of the critical path method.

Differences Between Critical Path vs. Critical Chain in Project Management

The following tables show the key differences between critical path and critical chain project management:

Feature	Critical Path Method (CPM)	Critical Chain Method (CCM)
Focus	Task sequence and duration	Task sequence, duration, and resource limits
Key Element	Critical path (i.e., longest sequence of dependent tasks)	Critical chain (i.e., longest path considering resource constraints)
Buffers	No built-in buffers	Includes buffers to manage delays and uncertainties
Resource Management	Assumes resources are available as needed	Considers resource constraints and their impact
Schedule Adjustments	Adjustments often require reworking the schedule	Uses buffers to handle delays without reworking the whole schedule
Impact of Delays	Delays on the critical path delay the whole project	Delays can be absorbed by buffers, thus reducing the impact
Task Prioritization	Focuses on completing tasks in sequence	Focuses on task completion while managing resource usage
Flexibility	Less flexible to changes in task durations or resource availability	More flexible due to the use of buffers and consideration of resource constraints

Summary

The critical path and critical chain method offer valuable approaches to project management. CPM focuses on task sequences and durations, providing a clear path to project completion but without built-in flexibility. On the other hand, CCPM incorporates resource constraints and buffers, allowing for better handling of delays and uncertainties. 

Understanding these methods can enhance efficiency and improve the likelihood of on-time project completion.

Further Readings:

• What is the Critical Path Method?
• What is Critical Chain Project Management?
• What is the PERT Chart?
• What is the Gantt Chart?
• What is the Precedence Diagramming Method?

This topic is important from a PMP exam point of view.