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Using the Critical Resource Path Print

We have all heard about the Critical Path Method (CPM) that analyzes a network of tasks and schedules them to produce the earliest project completion date while respecting the task dependencies.

The critical path is the sequence of tasks through the network from the start of the project to the end, in which each task contains zero slack (or float), meaning that a delay in any one of these tasks will delay the project completion date.

For years we have learned to manage by CPM and track the tasks on the critical path extra closely to ensure there is no delay in these tasks completing. Many people spend much of their time focusing only on the tasks on the critical path, thinking that they are minimizing risk by doing so. To some, this management method may well work, but it ignores risk in tasks not on the critical path. The critical path may well change several times during a project as "off-critical" tasks are delayed such that they now impact the project schedule and appear on the critical path.

Research over the past decade has indicated that there may be better methods of optimizing project schedules which take overall project risk in to account. Eliyahu Goldratt developed the Theory of Constraints (TOC) in 1986 (see the suggestions for further reading on this topic at the end of this article). Francis S. (Frank) Patrick, a management consultant and expert on practical applications of Goldratt's theory, explains that "the basic concept of a system constraint and the TOC Thinking Processes (a set of analytical tools based on cause-and-effect logic), applied to the project environment resulted in the development of the Critical Chain approach to project management." The Critical Chain Method (CCM) is another way of scheduling project task sequences (taking into account the common constraint of relatively finite resource availability) to minimize risk in the project delivery schedule.

The CPM does not address resourcing constraints and impact on the schedule, though when commonly applied using tools such as MS Project, most project managers will try to load balance their resourcing plan which may readjust the critical path. The CCM, on the other hand, does address a number of resourcing issues, and does somewhat better than the CPM on resource-constrained scheduling by building a project network based upon both task sequencing and resource dependencies. While the "critical chain" is the resource-constrained critical path, it fails to explicitly capture, like the CPM, the "soft issues", or human impact of people being scheduled on critical tasks for long periods of time.

Whether we use CPM or CCM, we often construct project networks which, due to resource constraints, have a key person working nonstop through much of the critical task sequence. While this cannot always be avoided, it can be adjusted to account for the human impact of this level of stress and the resulting increase in project risk. Picture yourself as one of these people -- working several weekends in a row, working late into the evening to help make up for delays, trying to meet the project milestones. In some industries, the ability to move a project end date is impossible and the project must make its delivery date. For example, consider a construction project building a speed skating oval for the winter Olympics. The building must be complete prior to the start of the games. It is very common for key people working on these critical tasks to become "burned out" as they sacrifice their family time, their sleep, and maybe even their health for the good of the project. How many times has a key person fallen ill near the end of a project as they have been pushing themselves too hard? How do you calculate and mitigate this risk? As project managers, we have to think of this when we build the project schedule, and look for what I call the Critical Resource Path.

If you have key people on a project, try to level their workloads, and then examine their utilization plan. In Microsoft Project, this is done by looking at the Resource Graph view. Anyone scheduled at 100% (or more!) utilization over a period longer than two weeks needs breaks scheduled in to the plan. Especially in disciplines such as software development or engineering, where you need a person to be mentally sharp all the time they are working on key tasks, we need to build plans that ensure people are able to operate at their best. This means we should have periods of less intensity (easier tasks, or lower utilization) to balance periods of high intensity.

The Critical Resource Path is any path (or group of paths) through a project network for which there is a key resource assigned who is planned to be working at high intensity for long periods of time. There is inherently a higher level of risk in scheduling work in this manner, and that needs to be documented and a plan put in place to mitigate the risk by adding scheduled breaks or periods of lower-intensity work. One of the evils of automated load balancing, is that it tends to create periods of consistently high utilization where before there were bursts of intense work with downtime periods in between. Many seasoned project managers know this instinctively, and refuse to use automatic load balancing features on scheduling software, instead preferring to perform manual load balancing to accommodate the working patterns of individuals and the intensity required to perform their assigned tasks.

The next time you build a project schedule where there are key people assigned with no readily-available help, map out one or more Critical Resource Paths through your network and see if there is hidden risk in the plan where you might be working someone too hard. You might be surprised at what you find.

Further Reading

For additional information on this topic, see the following resources:

Goldratt, Eliyahu M. Critical Chain. Great Barrington, Massachusetts: North River Press Publishing Corporation, 1997.

Theory of Constraints. Great Barrington, Massachusetts: North River Press Publishing Corporation, 1990.

Patrick, Francis S. "Critical Chain and Risk Management -- Protecting Project Value from Uncertainty (Part 1)" Focused Performance Web Site. 19 Feb. 2002

"Critical Chain Scheduling and Buffer Management . . . Getting Out From Between Parkinson's Rock and Murphy's Hard Place." Focused Performance Web Site. 19 Feb. 2002

Pierce, David R. Project Scheduling and Management for Construction. Kingston, Massachusetts: Robert S. Means Company Inc., 1998.


2002 © Kevin Aguanno

About the Author:

Kevin Aguanno is a Principal and Certified Senior Project Manager in IBM Canada's Business Innovation Services unit and former Executive Producer of IBM's Canadian Interactive Media Studio.
He is certified by IBM and PMI, and is a member of both PMI and the Association for Project Management (UK).
A published author and noted public speaker, he is currently the Best Practices Committee Chair for the New Grange Centre for Project Management.

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