Understand the conflict in Critical path analysis vs. longest path

There are several topics more valuable to your client when it comes to your project’s critical chain, critical path analysis in  Primavera  P6.

And the expectation is only YOU. A dear scheduler is an expert. So, YOU had entirely known your project’s Critical Chain/Path inside and out. And can do Critical path analysis.

But wait! ……Is it the Critical chain you should be reporting on, or the Longest Path?

In Primavera P6 the terms Critical Path, Critical Chain, and Longest Path are often used conversely when discussing on project’s super-high-priority sequence of work to deliver on time. It is very confusing to many. Also, there are some significant disputes about the differences.

The great news is that there is an important distinction between in Primavera P6 project’s Critical Path & the Longest Path, which is explained here.

What is Primavera P6 project’s Critical Path?

“It is the path of 0(Zero) Total Float through the project.”

The above description for Primavera P6 Critical Chain/Path is accurate but only in under a stringent set of conditions.

When is it true?

1. No Project Deadline

When a deadline is set for a project (i.e., Project Need to Finish By date in Primavera P6), then it results in the form of Total negative Float if you are late. It shows positive float if you are early. Hence, the path of 0(zero)-float activities disappears.

2. No Constraints

Primavera P6 Constraints affect an activity’s Total Float value. Constrained actions can show Total negative Float and can make a negative float to their successors or ancestors. Implementing constraints throughout a project will affect what activities are Critical. And therefore, again the path of 0-total float through the project escapes you.

3. No Actuals

In Primavera P6 a project with actuals may not show a path of 0-float. The actuals & the order of execution can influence the activities’ Total Float also.

Hence, it shows that the age-old “path of 0 Total Float” description doesn’t fit in our complex project environments.

And if you consider doing some digging online, you will find that our attempts to clear up the concept of “Critical Path” has led to infinite different ways to explain the term “Critical” for a project. Search, and you are expected to run into terms like:

• Criticality
• Near-Critical
• Critical Chain
• Critical Risk

What will be your Primavera P6 project’s Critical Path depends on and how you end up interpreting the term “Critical” and defining what activities are “Critical” according to you. You may have activities that you think “Critical” although the Primavera P6 software says their Total Float values. There’s a chance that you have activities that have positive Total Float but are Critical according to the clients. You may want to trace a specific path of operations through a project. This is called real-world project controls.

“Critical Path is a pathway through your project which has activities that YOU consider critical.”

What is a Primavera P6 project’s Longest Path?

There’s further clarity to be found here. The longest path is THE LONGEST path when there’s no disputing the term “longest.”

The Longest Path is the path through which a Primavera P6 project network from start to end where the Total Span is higher than any other path.

It makes sense to focus on a Primavera P6 project’s Longest Path as it is undoubtedly the path where variations from the plan will influence the project’s end date.

In Primavera P6 the overlap within Longest Path and Critical Path is possible?

The Longest Path is a Critical Path, but not all Critical Paths are Longest paths.

Because Primavera P6 we can modify Critical Path through actuals, constraints, deadlines and other mechanisms, usually we end up with a path that has many more Critical path activities that would be on the Longest Path.

If you begin with a baseline schedule that has no actuals, no constraints, and no deadline, and you perform some CPM scheduling on it, then the path of 0(zero) Total Float will be the Longest Path. If you added up the duration of all activities on that 0-float path, it would have the longest Total Span.

If you calculate the Longest Path for a Primavera P6 project that does have actuals, constraints, and a deadline, etc., then you will come up with a path of activities that are “important,” need I say “small-c critical” to the timely completion of the project.

Which one should be in use?

I would strongly recommend you get to know your Primavera P6 project’s Longest Path and monitor it. What the client wants to see might be something different, but the timely completion of Longest Path activities leads to your project ending on time.

Most software packages let you track both Critical Path and Longest Path.

Finally, I would promote educating yourself on how the Primavera P6 software that you use determines Critical Path analysis and what kind of things (constraints, relationships, lag, etc.) will alter an activity’s Total Float.