January 18, 2007
Critical Path – Where are you?
There is no question that the enhanced modeling capabilities of current CPM software have made CPM schedules more complex. In fact, in reaction to these advanced scheduling capabilities, some analysts have started a “back-to-basics” movement, attempting to convince owners to write scheduling specifications that prohibit the use of many of these advanced features. Such fears, however, are misplaced. When properly applied, the superior modeling features of CPM schedules can benefit owners and contractors, alike. But, to guard against misuse, contractors, owners, and schedule analysts must all become proficient in the application of these scheduling tools.
Too often, scheduling analysts are inclined to conclude that the schedules cannot be used because “the critical path makes no sense.” Such an important decision, however, must be closely scrutinized. And, while it may sound too simplistic, the first question that should be asked is “how have you identified the critical path?” In simpler times, the critical path was simply the path with zero float. This “foundation” of the scheduling world was an intuitive conclusion, drawn from an understanding of the way the schedule calculates dates through a network of finish-to-start relationships with no other logic constraints. But this foundation has been shaken by the power of the modern CPM schedule. In a current CPM schedule, an activity may have zero float for a variety of reasons, including something as simple as a zero total float constraint.
With the additional logic that can be added through the use of the advanced features now available in most CPM scheduling programs, the longest path may have zero float along its entire path, a portion of its path, or nowhere on the path. This means that it is possible, even likely, that certain activities on the critical path will actually have float! Again, this is OK. If these features have been used properly, a close look at the schedule logic will reveal why the float on these activities makes sense. Often, this float is a function of a constraint that is modeling a contract requirement or other known construction restriction.
A properly implemented CPM schedule is a dynamic tool that lives throughout the duration of the project. The critical path is equally dynamic. As the project progresses, the schedule should be updated to reflect both the actual project progress and any logic revisions that are necessary to better model the plan to complete the project. Some logic revisions may be necessary to reflect a change in the contractor’s plan. Other revisions to the logic may be necessary even though the plan hasn’t changed. This is because, as the actual progress is entered and the schedule is recalculated, certain logic needed to improve the model may become apparent. For example, the previous update may have forecast a start date for work in an environmentally sensitive area within a time period allowed in the permit. However, in the current update, the schedule is now forecasting the work to start during the restricted period, highlighting the need to constrain the start to occur after the restricted period has passed. This does not mean that the original schedule was flawed. Rather, such revisions reflect the normal dynamics of the project management process.
The critical path may be so dynamic that it changes from day to day. While such a degree of change is unusual, critical path shifts between updates are quite common. This results from the fact that, as the project progresses, the lengths of the paths relative to one another change. For example, as the steel erection work on the longest path makes progress, the remaining duration of that path becomes less. Conversely, as the masonry work on a shorter path fails to make progress, the remaining duration of that path remains the same. If this condition continues, the day will come when the remaining duration of the masonry work path will equal the remaining duration of the steel erection path. On that day, both steel erection and masonry are concurrently critical. On the following day, the lack of progress of the masonry work begins to critically delay the project.
Understanding how to identify shifts in the critical path is essential to properly allocate critical project delays. In the preceding example, the lack of progress of masonry work does not delay the project until its path of work becomes the longest path. The analysis techniques employed by your expert should be such that the critical path of the project is known for every day of the project. The advanced features of current CPM software have given us powerful tools that provide a high level of precision in the analysis process. While these precise calculations still need to be interpreted in the context of the specific facts of each project, the broad-brush techniques that used to be commonplace are a thing of the past.
Abracadabra – Now you see it, now you don’t
To some, the analysis of delays seems to be more fiction than fact, especially when it comes to mitigating the effects of earlier delays. Again, an understanding of the basic concepts sheds light on the mystery. The determination of a delay is itself a prediction based on an established plan. When a project experiences critical delays, the existence and magnitude of the delay is function of the resulting affect on the forecast project completion date based on the existing plan to complete the project work. One way to mitigate this effect is to change the plan. Thus, the project may experience a critical delay that is then mitigated by revising the schedule logic to model a new plan. While this may seem like black magic, this is actually the purpose of the CPM schedule as a project management tool. The schedule models the plan and predicts delays so that corrective action may be planned and taken to overcome these delays.
When critical project delay is mitigated by logic revisions, it is possible that one party may be responsible for the delay while the other is credited with the savings. Typically, unless directed by the owner or derived from a waiver of a contract requirement, the savings is credited to the contractor. This is because the contractor is generally entitled to determine the means and methods used to execute the work. When it is necessary to alter the means and methods to mitigate delay, the contractor takes on the risk of successfully executing the work in accordance with the new plan.
While crediting the contractor with this projected savings may seem unfair because the contractor has not actually accomplished the savings, if all of the critical project delays and saving are identified throughout the project, the correct answer will result. This is the case because the contractor is expected to complete the work according to its revised plan. For example, if the contractor mitigates a delay by shortening the duration of a critical path activity from 20 days to 10 days, the contractor is credited with a 10-day savings. If, when performing the work, the contractor takes 20 days to perform the work and it is still critical, the contractor will be credited with a 10-day delay. Thus, if the contractor cannot actually accomplish the savings, no net savings is credited.
Problem Solved?
For a party in a dispute involving delays, there should be no mystery when it comes to determining what truly delayed the project. While today’s CPM schedules are more sophisticated than their predecessors, the underlying principals remain simple. The expert you choose should be able to quickly assess the nature of the available documents and describe a credible approach to determining delay. Criteria for abandoning the schedules should also be discussed. And, the intended techniques and methodology for determining critical project delays should be explained in detail. Be wary of techniques that you don’t fully understand. After all, if your expert can’t explain it to you, the judge and jury won’t get it either.
Parts 1 and 2 of this article can be viewed at http://www.lorman.com/newsletters/view_past.php?category_id=3&year=2006.
William A Manginelli is the President of Trauner Consulting Services, Inc. in Philadelphia, PA. Learn more about Trauner Consulting Services, Inc. at http://www.traunerconsulting.com. He can be reached at (215) 814-6400 or at [email protected].