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Categories: Theory of Constraints
Introducing Critical Chain Project Management

Introducing Critical Chain Project Management

By Bob Sproull


In my last post I presented another reason that the Critical Path Method (CPM) for managing projects has such dreadful completion rates, bad multi-tasking.  We summarized all that we have learned that is causing such terrible results when using the Critical Path Method (CPM) which are:

  • We’ve learned that task time estimates for tasks are artificially lengthened as a protective measure against Murphy and all of the negative baggage he brings to the party.
  • We’ve learned that even though this safety is built in, it is wasted because of the Student Syndrome and Parkinson’s Law.
  • And finally we’ve learned how devastating bad multi-tasking can be to the completion rate of projects.

In today’s post, we will begin our discussion on an alternative project management method known as Critical Chain Project Management (CCPM).


Critical Chain Project Management

As we’ve seen in CPM, task durations are inflated to protect against Murphy.  What if we could significantly reduce these imbedded safety buffers and still provide the protection that we need? Suppose we were able to reduce the estimated duration by 50 % and still protect against Murphy.  In other words, if we could complete the tasks in 5 days instead of 10 days, wouldn’t this be a quantum leap in project completion time reduction?

Project Time Reduction

In the above drawing, we have reduced the time to complete these three projects from 30 days to 15 days, but can we do this and safely guard against the uncertainty introduced by Murphy? 

CPM defines the critical path as the longest path of dependent tasks within a project.  That is, tasks are dependent when the completion of one task isn’t possible until completion of a preceding task.  The critical path is important because any delay on the critical path will delay the project correspondingly.

The figure above is an example of a series of tasks which must be completed in a project with the critical path highlighted in grey. Traditional project management (i.e. CPM) determines the critical path by looking at the task dependencies within the project. In our drawing above, Task A2 can only be initiated after A1 is completed.  Task B3 can only be performed after completion of B1 and B2. Task D1 can only be performed after completion of A2, B3 and C2.  Using CPM the critical path would have been identified as C1-C2-D1 and the project completion estimate would have been 29 days (i.e. 8d+12d+9d).

In addition to task dependencies there are also resource dependencies that CPM fails to recognize.  What if, in our example above, tasks A2 and B3 are performed by the same resource?  Is the critical path different?  In the figure above we see the new critical path that includes a provision for resource dependencies and as you can see the new critical path is A1-A2-B3-D1 or 5d+10d+10d+9d equals 34 days.  So the minimum time to complete this project is now 34 days.

In my opinion, the failure to consider resource dependencies is one of the key reasons why project completion rates are so terrible. The simple implication of incorrectly identifying the critical path, which we will now refer to as critical chain is that the project team will never be able to complete their project on time without heroic efforts, adding additional resources, overtime or a combination of all three.The practical implication of incorrectly identifying the real critical chain is that the focus will be on the wrong tasks.  In TOC, this is identical to working on non-constraint process steps, thinking that product will flow through the process at a faster rather by doing so.  We all know that the focal point for “speeding up” any process is the system constraint.


Next Time

In my next post we’llcontinue our discussion on CCPM and demonstrate why it is such a powerful method for completing projects on time, on scope and on budget.  As always, if you have any questions or comments about any of my posts, leave me a message and I will respond. 

Until next time.

Bob Sproull

Bob Sproull

About the author

Bob Sproull has helped businesses across the manufacturing spectrum improve their operations for more than 40 years.

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