Primavera P6 users know that it’s important to identify the longest path through the activity network; longest path activities cannot delay without postponing project completion.
If you want to optimize your P6 schedule, i.e. shorten its duration, you will want to look to fast track and/or compress activities that are part of the longest path. How do you know, in Primavera P6 Professional, when an activity is along the longest path?
First look for critical activities. Critical activities are displayed as red bars on the Gantt chart. But, depending on the scheduling option settings in Primavera P6 Professional, not all critical activities fall on the longest path.
Yes, there are two ways to define a critical activity in Primavera P6 Professional; either activities that have total float less than a specified period of time, say 0-hours, or activities that are on the longest path. If the scheduler has defined critical activity as having total float less than a certain time period, a critical activity may or may not be on the longest path. In this scenario an activity may be critical in respect to an activity constraint date, and not the completion of the project.
So, a critical activity is in danger of delaying either a constraint date or the project completion date. If your immediate concern is project completion you will want to specifically identify all critical activities that are longest path activities. In Primavera P6 Professional it is possible to mark and/or filter all activities that fall along the longest path.
This article demonstrates a quick tip in Primavera P6 Professional to identify all activities that fall on the longest path.
Below in Figure 1 is our demonstration project.
On the Gantt chart we find that a number of activities have red Gantt chart bars and are critical. The question is how do we find out which critical activities are also longest path activities?
Let’s first see how we are defining critical activities in our Primavera P6 Professional schedule. In Figure 2 we find that critical activities in our schedule are defined as having total float less than or equal to zero hours.
So a red Gantt chart bar in our schedule does not necessarily indicate that a critical activity is on the longest path. It could be critical in relation to an activity constraint.
After further inspection of Figure 1 we find that our schedule has a Finish On or Before (FOOB) constraint on Install Conduit. This constraint is generating two days negative total float on Install Conduit and other upstream activities, namely Grade Site and Mobilize. But this still does not definitively indicate which of these activities are on the longest path or not.
An activity could be critical in relation to our FOOB constraint and/or in respect to the project’s longest path through the network. To find out which critical activities are also longest path we have to look beyond the Gantt chart.
In Figure 3 we include two additional columns from the general category to our activity table, critical and longest path.
Figure 4 displays the schedule, including the critical and longest path columns in the activity table.
These two columns tell us definitively which activities are critical and which activities are critical and longest path. Further review of these columns reveals that Mobilize is both critical and longest path. And Grade Site and Install Conduit are critical but not longest path.
A delay in Grade Site and Install Conduit affects our FOOB activity constraint, and a delay in Mobilize affects the constraint and project completion. A delay in Mobilize therefore would have a more negative affect on the project than an equivalent delay of Grade Site and Install Conduit.
Another way to learn which activities are longest path is to implement the following longest path filter, Figure 5.
This filter captures all incomplete activities that are on the longest path. Figure 6 presents the demonstration schedule using this filter to display the longest path through the network.
Note the Filter All: Longest Path label, Figure 6. It is interesting to note that the Project Management Level of Effort (LOE) activity is considered a longest path activity. It, however, is not critical; it will not delay project completion. It simply expands and contracts to match the duration of the longest path.
The Gantt chart is a good place to start, but not definitive in specifying longest path activities. In addition to the Gantt chart you must know how critical activities are defined in Primavera P6 Professional.
View the schedule log file to find out if the schedule defines critical activities as longest path or not. If it does than all critical activities are along the longest path. If not, a critical activity may or may not be along the longest path. Display the longest path column in the activity table to find out conclusively if the respective activity is along the longest path through the schedule network or not.
It is also possible to capture all longest path schedule activities with the longest path filter. Schedulers should note that LOE activities can be longest path, but not critical.