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Driving & Free Float Activity Properties In Primavera P6

24 November 2015

Find out how to spot if one or more tasks are encroaching on an important activity's start date.

Imagine a large project with many tasks and associated relationships, and you have a critical task with an important start date. Do you have a quick way of spotting all the predecessor activities that may be encroaching on this critical activity’s start date?

As projects become larger it becomes increasingly cumbersome to analyze the effects activities might be having on one another. Yes, if the Gantt chart bar is red you know your activity start date is important. But what activities do you need to watch out for? These are activities that with only minor delays could cause your important task’s start date to slip. This is where the term ‘Driving’ activity comes into play.

Another term you also want to become familiar with is ‘Free Float’. By tracking the both ‘Driving’ tasks and ‘Free Float’ you can quickly focus your efforts on all activities that could delay your important task.

This article explores the value and how to track ‘Driving’ relationships, as well as, activity ‘Free Float’ in Primavera P6 Professional. That way you will be able to spot if one or more tasks are encroaching on an important activities start date.

The Situation

We have in Figure 1 a pictorial of an important activity in red that is slipping from its baseline in yellow and three predecessor activities.

Driving and Free Float Activity Properties Fig 1

Figure 1

The question is which one of these predecessor activities is the culprit that is causing the critical activity to slip? From our cartoon pictorial you can’t tell. Okay, the pictorial in Figure 1 is an over simplification of your problem. But the reality is for large projects you most likely will not see all the predecessors lined up on the Gantt chart in a stack one on top of the other like in our diagram.

You also will find yourself scrolling back and forth through your Gantt chart looking for all the predecessors that encroach on your important task. Yes, and the blur of sorting through a large project just might make it appear that all your predecessors have the same original durations, as in our cartoon.

Driving Tool

What you need to find out, and quickly, is which predecessor activity is driving your successor activity. In other words, which one of the predecessor tasks determines the start date of the important successor task? The quick solution to this situation is to display all the predecessor activities in the bottom details as in Figure 2.

P6 article figure 2

Figure 2

Using the predecessors tab we can stack all the predecessors to our important task one on top of each other for easy viewing of their properties. And the property we definitely want to list is ‘Driving’. The predecessor that is the culprit will have a check mark in the ‘Driving’ property column. In our example activity B is check marked to alert us that that activity is determining our critical activities start date. In our example it is easy to decipher this from the Gantt chart, but, again, for large projects this might not be so apparent on the Gantt chart. So listing the predecessors and their ‘Driving’ status speeds up activity analysis.

Free Float Tool

One more thing. Why not list ‘Free Float’ along with ‘Driving’ as we do in Figure 2. Yes, in the predecessor’s bottom details tab you can list the Free Float of each predecessor activity. ‘Free Float’ lets you know how many days you can delay an activity before it delays a successor activity. The ‘Free Float’ of the ‘Driving’ activity, of course, is zero. Wouldn’t it be nice to spot activities that are not ‘Driving’, but could become ‘Driving’ with only minor delays?

In Figure 2, the Free Float of activity C is 1-day. That warns us that this activity is encroaching on our important task, even though it might not be the ‘Driving’ activity. Thus, ‘Free Float’ is a nice complement to the ‘Driving’ property, and you can display both in the predecessors bottom details tab in Primavera P6 Professional.

Summary

As projects become large, activity relationships become more cumbersome to analyze. There are tools in Primavera P6 Professional to help you locate, even in large projects, exactly which activity may be causing your important task to slip.

The first goal is to list all predecessor activities, which you can do in the bottom details predecessor tab. Having done this one handy feature in Primavera P6 lets you know which activity is the ‘Driving’ activity.

The ‘Free Float’ is a second tool that complements the ‘Driving’ activity. It shows you even non-Driving activities that may be encroaching upon your important successor task. So ‘Driving’ and ‘Free Float’ are two activity properties you’ll want to make part of your common scheduling vernacular.

Source: TenSix Consulting 

 

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