I attended an end-of-project meeting a few years ago. The
project was relatively successful, but the participants were talking about things
they could have done better. The client stated that more time should have been
spent in training. The project manager replied, “I agree. Next time I will
place training on the critical path.” A little later the project manager noted
that she should have placed client approvals on the critical path so they were
completed sooner.

At that point I had to jump in, since the term “critical
path” was not understood correctly. “Critical path” refers to the sequence of
activities that must be completed on schedule for the entire project to be
completed on schedule. In fact, the activities on the critical path may not be
very important at all. The critical path may include very mundane activities.
The critical path is “critical” because it drives the end date. If the end date
for the project has slipped, it is because at least one activity on the
critical path did not complete on time.

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A layman’s description of critical path

On every project, no matter how complicated, there are
always some activities that can be started earlier or completed later without
jeopardizing the final completion date for the project. This flexibility
between the earliest time an activity can
be completed and the latest time when it must
be completed is called”float.” By definition, if an activity has
flexibility, or float, associated with its start and end date, then it is not on the critical path.

Let’s look at those activities where you do not have the
flexibility in the start and end dates. These activities can’t be completed
earlier because they’re waiting for the completion of another activity. They
also can’t be completed later than scheduled without causing all the succeeding
activities to be late. That’s because none of the activities that follow have
any flexibility, or float, in their start and end date. All of these activities
back up tightly against other activities that precede or succeed them. The
critical path consists of the longest sequence of activities from project start
to end that must be started and completed exactly as scheduled. In other words,
it is the longest sequence of activities with zero float. If any activity on
the critical path is late, the entire project will be late (unless the time can
be made up somewhere else on the critical path).

A layman’s description of critical path II

The project end date is what it is because of the critical
path. If there were not a critical path, there would be at least some float in
all the activity paths from the start of a project to the finish. If there were
float on all paths, you could squeeze the float out and finish the project
earlier. As you moved the end date to finish earlier, you would start to remove
some of the float. However, at some point, the float would be gone from one of
the paths. This would be a point where each activity on at least one path would
have start and end dates that backed up against each other. There would be no
more float on this sequence of activities. This would be the critical path.

Why is it important to understand the critical path? It is
important because you can’t effectively manage your workplan
without understanding the critical path. If your project is running late, you
need to know the critical path since that is the only way to accelerate the
timeline and get back on schedule.

Want to know more? Read more details on how to manage the
schedule using critical path in next week’s column.