Can there be multiple Critical Paths, if so which one?

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MikeCOYS
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Hi everyone!

I have a question regarding the Network Diagram and the critical paths.

I understand to find the critical path we must connect all the floats with weight 0.

However, what if there's more than one path with weight zeros?

For example (assume all below paths have zero weights/floats, and duration beside it):

+ A, C and G (duration 3, 3, 2 = 8),
+ A and D (duration 3, 4 = 7)
+ B, F and H (duration 1, 5, 3 = 9) <---- longest duration.

All three of the above have critical paths of weight zero (determined from floats).

Which path would be the correct one, is it...

... all of them?

... or the one with the longest duration?

I'm confused, can anyone help me out please?

Thanks in advance.
David Biggins
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Mike,

I think the confusion is caused in part because your network diagram is quite small. As the network diagram increases in size, the chance of generating more than one critical path diminishes.

You need to take into account the dependencies of activities which means you follow the path in the network diagram which has the longest overall duration in order to identify the critical path. In your case B, F & H.

The other two are not critical paths paths because they do not have the longest duration. For example, task A may be able to slip by duration = 1 and not affect the overall plan. I would check the back path through the diagram to ensure the calculations are correct.

It is perfectly feasible to have a small plan with more than one critical path. In that case, all the tasks on the multiple critical paths are critical which means that a delay in any one of those tasks will cause a delay to the completion of the project.

Best wishes
David
David Biggins
MikeCOYS
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I was confused because from what I learnt, critical paths are paths of activities with zero floats. By that knowledge, I was stumped when more than one critical paths appeared. But I also knew longest path equals CP.

From what I understand, there could be multiple CP's, and for each path from start to finish the duration varies. To find the 'true' CP, we have to eliminate the shortest CP's.

Much clearer now. One more question, what if there's multiple CP's with same duration?

What I think is that each one would be fine, but the one to take would be dependent on the organisation right? Like their methodology in processing activities, such as Shortest Processing Time (scheduling rule), etc.

Mike.
David Biggins
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Hi Mike,

The critical path is less a route that you take and more an indication of those tasks in the project that affect the end date if they are completed early or finish late. All the tasks in the plan will need to be completed. Of these tasks, the ones that directly affect the end date are the critical ones and these will require special monitoring to control them.

This might answer your question about the two paths?

Best wishes
David
David Biggins
pilotage
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David,

Forgive me if you answered this, but I too have what appear to be two CPs that have zero slack. Can I assume that both of these are critical given there are an equal number of nodes?
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kwalford
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pilotage - Yes, if there is no slack on every path (both critical). In your case you need to monitor both of them. During the project, it is possible that circumstances may change and you may only be left with one critical path, or a new one entirely.
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dhaughey
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Hi Pilotage,

Having multiple critical paths reduces the likelihood of project success since there are too many critical tasks that may impact the planned completion date. I would suggest checking the schedule to ensure there is no slack in any of the identified critical paths. Review your dependencies, are they correct? Does the schedule reflect reality; if not, update it to show your realistic expectations for the project. Monitor the critical paths as the project progresses for changes that impact the planned completion date.

Duncan
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kwalford
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Multiple critical paths = greater risk!
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