Setting the Critical Path

The reality of the matter is, more than a few have used the wrong schedule calculation settings and filters from day one. Unless persuaded to change, they will do so indefinitely.

Again, as in previous article, we refer to the primary path when talking about critical path unless specifically described as another.

The first one we will discuss is the longest path, followed by Total float equal or less than zero. Third on the line is the Path with the lowest Total Float (it can be positive, zero or negative), and last but not the least, one defined by the contract (the client’s definition of criticality or the “it depends” critical path).

Together, let us review how the Longest Path (LP) compares to the calculation using Total Float (TF). These are the two main approaches. Both represent the critical path and fundamentally cover how we would deal with the third and the fourth criteria.

Criteria 1: Critical Path is the Longest Path

A scheduling default and most commonly used critical path definition uses the longest path on the Schedule Option dialogue box. The Primavera scheduling tool can identify critical activities without specifying any total float value by merely saying “Yes” to the longest path filter and following additional setting prescribed by the tool.

It will identify the primary critical path from the last activity of the open schedule up to the earliest and back. The longest path is the longest path in the open schedule network from start to finish.

Criteria 2: Critical Path is  Total Float < =  Zero

The second method most frequently used is to filter critical activities by specifying a total float less than or equal to zero. Many agree that this method of identifying critical path is arguably more widespread.

The simple rationale: If any activity is contributing to the delay of project completion, then it must be critical. It does not have to be in the primary path nor directly contributing to the delay. If the project will miss an important a mandatory baseline milestone, then the tool generates a critical path from that milestone.

Primavera uses Total Float < = 0

as its default setting. Activities (including relationship lines) with a Total Float value of 0 (or less) are shown in red on the chart. If they did not turn to red, there is probably an existing project constraint. The planner/scheduler should check the “Must Finish By” field on the Project Window.

If not needed, just remove the “Must Finish By” project constraint and let the schedule flow freely. If for some reason it is needed to be there and the project is finishing earlier than the Must Finish By date, then there would be no critical path generated from the criteria TF < = Zero.

It is one of those occasions where the Longest Path delivers the critical path perfectly by showing an unbroken path along critical activities. This illustrates the true critical path, the longest path.

It is the path with the longest overall duration. Its duration is the project overall remaining duration.