The True Critical Path

In my experience, the first pass critical path assumes unlimited resources. The critical path may change after resource leveling but it is always the longest path to completion.

I guess what you are saying is that in the projects you have analyised activity duration is driven by resource availability. This is quite often the case, but not always.


Consider the theoretical schedule of getting ready for work in the morning.

You need to perform the following activities:
- Have a Shower
- Brush your teeth and hair
- Iron your clothes
- get dressed
- cook breakfast
- eat breakfast

Assuming that each activity takes 15 minutes, the critical path is 45 minutes.

If you live alone the critical path changes to 1.5 hours

if you have a girlfriend/wife/mother to help you the critical path is 1 hour.

The important point to take from this is that without first preparing the first pass critical path (unlimited resource) you wont know what to ask your wife to do for you.

Brenan,

I condider your excelent example, however in the real world using advance software and traditional computation, it seems to me the true meaning of critical path is somehow violated in a sense that during the backward pass computation, it does not calculate the true activity float due to the fact that the resource constraints are not being considered in the backward pass , it means the availabity of the true resources is completely ignored..

The true critical path as what i believed should take into consideration of all schedule constraint to include unit resource or money..

This is a healthy conversation Brenan.. regards

Ulysses,
please look at http://www.spiderproject.ru/library/london.ppt
I agree as you can understand from this presentation.
Regards,
Vladimir

Vladimir,

I have had a look at the ppt presentation.
I agree with your proposition that the "true" duration of the project must take the resource limitations into consideration.
But that does not mean that classical CP is "wrong" or "erroneous" (this is the word you use in the ppt).
That resources are not a consideration is merely a starting assumption for classical CPM.
The shortest possible duration of the project based on classical CPM is obviously the most optimistically short duration that can be hoped for. It is a good starting point. It should not be what any contractor signs up to.

Trevor,
I agree. Classical Critical Path defines time limitations and may be helpful. But it does not show which activities are really critical when resources are limited. If somebody will follow the definition that all schedule constraints shall be considered when determining critical activities and critical path then classical critical path is a wrong answer.
There is a need to be able to determine both - classical Critical Path to learn most optimistic project duration and Resource Critical Path to learn which activities are really critical, what project duration is feasible with the available resources.
Regards,
Vladimir

ulysses,

I totally agree with you, I have seen many projects tracking progress against early & late target curves. I think this is a very dangerous practice... in most cases if you are tracking near the late curve, the resource requirements to maintain this will be impossible. I think the late curve gives too many project managers a false sense of security.


I prefer to communicate a schedule as a critical path network, S curve and resource profiles (based on early dates). If progress falls too far behind the early curve the work needs to be reprogrammed, new progress targets set and the resource requirements reassessed.

Vlad wrote ; If somebody will follow the definition that all schedule constraints shall be considered when determining critical activities and critical path then classical critical path is a wrong answer.

Absolutely I aggree with vlad, I guess the inventor of convetional CPM is unable to foresee the true critical path becuase of limited tools way back in the year 50’s ..