Displaying "most critical" path (i.e. path with most negative slac

[bari_sax]

I have a project that is running a bit behind schedule for a given deadline.
Almost all the tasks have some negative slack, and therefore the critical
path is shown for multiple parallel paths, even though some of these have
less "negative" slack than others. This makes it hard to find the wheat in
the chaff.

What I'd like to do is highlight the "most critical" path, namely the tasks
that have the most negative total slack. This will help us target the key
tasks that will bring us closer to deadline. Is there a way to display this?
(Perhaps by flagging those tasks that all tie for the maximum negative total
slack, then formatting the bar styles to pull out this flag?)

 

[Rod Gill]

I'm not sure that will show you the real "truth". Best to remove every
constraining date you can. If a task has to have a date, then it must be
affected by a constraint (EG contractor not available until Date X). Create
separate milestones for each constraint and have them at the top (or near
the top of your schedule) with a note explaining the constraint and the
relevant date. Link all tasks affected by this constraint to the constraint
milestone. No other tasks should have a constraining date.

Create a view that shows total slack (or insert the total slack column) and
look at all tasks with total slack that show tasks that in theory, can
finish towards the end of the project. these tasks may well have a link
missing. review all large values of total slack and add missing links where
necessary.

Your critical path should now be reasonably accurate and undoubtedly the
finish date will be after your required finish date. You now need to add
resources to reduce durations, add overlaps between tasks (-ve lag) and
eliminate as many constraints as possible, or at least bring their dates
forward. Continue until the project finish date is before your required
finish date.

Where you have required delivery dates, do not use constraints to show them,
instead add a deadline date. (Double-click the task, click the Advanced tab
then set a deadline date.) Deadline dates do not affect task dates but do
affect the critical path.

If you still can't get the finish date early enough your project may not be
able to finish on time, so review its goals and either demand all the
resources you need to finish on time from management or cancel the project
if the date is not negotiable.

Good luck!!

 

[Trevor Rabey]

Rod,

You beat me to the answer but I want to support your very first paragraph
100%.

(bari_sax, please take the advice)

This approach of stripping off all the constraints and letting the project
flow to wherever it wants to or must go, so that there is only one CP and
those C Tasks all have zero Total Slack, is so utterly natural that it is
hard to see why people are so fond of forcing in-decipherable negative slack
into the plan in the various ways that it is done. Even if the scope is
properly defined in sufficient detail etc, distortions caused by
constraints, deadlines and weird predecessor links completely mask the CP,
yet finding this darn CP is the whole point of the planning exercise.

Putting in the contract dates at the top in a separate section, for
reference but absolutely(?) not linking them to anything else, especially as
Successors, has been a favourite of mine forever. Some constraints such as
"someone can't start until...", "some part of the site will be available
on.." can be used as Predecessors, maybe, but no Successors in here.

Deadlines have to be stripped off too, because they create negative slack. I
got a surprise when I discovered this because I had assumed that Deadlines
did nothing more than put a little icon on the chart and in the Indicators
column.

It takes some fearlessness, though. It is very bad news to see that the
project duration blows out to say 100% more than you have signed a contract
to achieve, even after careful modeling (with an absolute minimum of
constraints, and SS, FF, SS links and no negative lag) and then throwing in
Resources to get durations down to the point where they are not even
plausible.

This is the price of making committments without doing the planning first
and establishing feasibility, and very common practice.

 

[Trevor Rabey]

You can Group By Total Slack or Filter By and/or Sort By Total Slack.

 

[John]

I have a project that is running a bit behind schedule for a given deadline.
Almost all the tasks have some negative slack, and therefore the critical
path is shown for multiple parallel paths, even though some of these have
less "negative" slack than others. This makes it hard to find the wheat in
the chaff.

What I'd like to do is highlight the "most critical" path, namely the tasks
that have the most negative total slack. This will help us target the key
tasks that will bring us closer to deadline. Is there a way to display this?
(Perhaps by flagging those tasks that all tie for the maximum negative total
slack, then formatting the bar styles to pull out this flag?)

bari_sax,
First let me state that I too fully agree with Rod's suggestions.
Nonetheless, we had an identical situation in our schedules and
unfortunately the way our schedules were set up, (formal change control
and too heavily based on externally generated earned value metrics), we
had to work the negative slack as best we could, if nothing more than to
point out to program management just how deep in the yogurt the schedule
really was. I used the simple approach of filtering first on the Total
Slack field and then on Start Date. What that gave us was a display of
the multiple critical paths with the worst path at the top of the heap.

John
Project MVP