Critical Chain Project Management

Critical Chain Project Management (CCPM)

CCPM is used when projects have schedule and resource constraints that must be effectively managed in order to meet project goals. It is a variation of the Critical Path Method (CPM) used in Predictive Project Management. CCPM was created out of a need to get more projects completed more quickly while working within a constrained pool of resources. Just like Agile methods, CCPM requires a maturity level within the organization based on Predictive Project Management methods in order for it to be successful. The basis of CCPM to deliver projects more quickly is to overcome the following phenomenon:

• Parkinson's Law: Work expands to fill the available time.
• Student Syndrome: People start to work to their fullest only when a deadline is near.
• Multitasking: Multitasking can delay the start of the successor tasks and makes us less efficient.
• Common cause variation: There is normal variation that occurs in estimates and probability of completing a task early, on time, or late.

The CCPM method begins with the same Predictive Project Management method used to determine the Critical Path. The project does need a clearly defined goal and objective, as well as a detailed list of activities to be completed in order to produce the expected result. During the Planning Phase when the schedule is to be built, instead of using the Critical Path Method (CPM), the Project Manager would use the Critical Chain Method.

SCHEDULING IN THE CRITICAL CHAIN METHOD

The Critical Chain Method utilizes techniques to prepare a resource-constrained project schedule with the most optimistic schedule dates. In order to do this, CCPM takes advantage of the probabilities of the successful completion of activity durations, removes built-in estimate safety, and adds duration buffers that are non-work scheduled activities to manage risk.

Managing Buffers in CCPM

With a Critical Chain project schedule, the Project Manager is concerned about the starting time of a sequence of activities and the duration of the sequence of activities. To do this, the Critical Chain Project Manager manages the buffers (as opposed to managing individual activities in the Critical Path as in Predictive Project Management). In managing the buffers, the Critical Chain Project Manager protects the actual duration sequence and hence the completion time of the project.

The following chart shows how the buffer management is done:

	1st Third Buffer Penetration	2nd Third Buffer Penetration	Final Third Buffer Penetration
1st Third Activity Sequence Penetration	NO ACTION	Serious problem; immediate action	Very serious problem; aggressive action
2nd Third Activity Sequence Penetration	NO ACTION	Define the problem and formulate a solution	Serious problem; implement the solution
Final Third Activity Sequence Penetration	Task sequence will be ahead of schedule	NO ACTION	Monitor the situation for any further action

In this chart, you are comparing the percentage of work completion in an activity sequence (Activity Sequence Penetration) with the consumption of the buffer at the end of that sequence (Buffer Penetration). Once a sequence of activities is started, as long as those activities are completed within the allowable duration, no buffer time is used. For example, 1/3 of the work in the activity sequence is complete and you've consumed 1/3 of your buffer, then no action is needed at that point, other than to continue to monitor the amount of work completed compared to the amount of buffer consumed. If an activity is completed early, the time can be added to the buffer. If an activity in the sequence is completed late, then this consumes some of the buffer time. The Project Manager monitors this buffer consumption and as long as it is in line with the completion percentage of the project, then little action is needed.

When you need to begin taking action is if you are consuming your buffer at a higher rate of speed than you are completing the work in the activity sequence. That implies that you will run out of buffer, which also means your project will be delivered late and probably also over budget. For example, if you've completed only 1/3 of the work in the activity sequence (Activity Sequence Penetration) but you've consumed 2/3 of your buffer, that means you only have 1/3 of your buffer left to cover any late delivery of 2/3 of your work. That is out of balance and would require significant action, likely an approval to add more buffer and more budget. In this way, the Critical Chain Project Manager is more concerned with managing the duration of a sequence of activities and buffer penetration rather than being concerned about each individual activity completing on time.

Implementing CCPM

Implementing Critical Chain Project Management requires a high level of Project Management Maturity within an organization as well as preparation, training, and a mindset shift from Predictive Project Management. Organizations that implement CCPM can not be concerned about measuring such things as employee utilization (measurement of how busy employees are) as the focus for the project work is how fast the activities can be completed with quality results. Resources can't be distracted with other work activities, or otherwise slow themselves down from achieving the aggressive duration estimates in the Critical Chain.

"The best analogy to use to explain the different mindset associated with CCPM is to think about how a Relay Race is run. How does a Relay Runner act? At the start of the race, the first runners arrive early, prepare, and wait for the start. As soon as the race starts, they run as fast as possible. The next runners in the relay are ready and waiting. They are not asked to "make good use of their time" or to "increase their utilization" by working on something else while they are waiting. They wait, so they are able to start running as soon as they get the relay baton. And then all they do is run their leg of the race without being distracted by other activities."