October 23, 2023
Challenges and Considerations in Identifying and Analyzing the Critical Path
This is the first blog post in a five-part series that discusses potential challenges and steps to consider when identifying and analyzing the critical path.
This post discusses the purpose of time management on construction projects, the second post concerns defining the critical path, and the third post addresses steps for assessing whether the critical path is valid. The fourth post concerns critical path schedule quality checks, and the fifth discusses steps to consider for identifying the critical path.
The Time Management Function
The main purpose of the time management function for a construction project is to plan, schedule, control, and monitor the timely completion of the project’s scope of work. The standard method for accomplishing these tasks, used throughout the construction industry, is the Critical Path Method (CPM) scheduling technique. AACE International’s Recommended Practice No. 10S-90 has defined the CPM scheduling technique as follows:
- Technique used to predict project duration by analyzing which sequence of activities has least amount of scheduling flexibility. Early dates are figured by a forward pass using a specific start date and late dates are figured by using a backward pass starting from a completion date.
- Network scheduling using activity durations and logic ties between activities to model the plan to execute the work. CPM scheduling is the method of choice for managing projects of long duration, complex technical integration, or the need to coordinate fast or early completion of the work.1
The all-important analysis capability provided by the CPM scheduling technique is to determine the work activities and sequences that comprise the critical path. The critical path represents the longest path or overall sequence of tasks and milestones that determine the project’s overall duration. Activities not on the critical path will have some degree of float or slack time. Activities with available float or slack time can be delayed by the number of float or slack days without delaying the project’s overall finish date.
Project stakeholders must know, with a high degree of certainty, that the forecasted dates on the critical path are accurate. Accurate information is needed for making sound and informed decisions relative to planning the remaining work, applying resources, dealing with potential delays, or accelerating portions of the project scope. CPM scheduling programs allow users to select activities on the critical and/or near-critical paths by filtering the schedule data based on low float values or the longest path criteria. The critical and near-critical path output is typically in bar chart or tabular report format.
Unfortunately, for large and complex engineering, procurement, and construction (EPC) projects, identifying, summarizing, and evaluating the critical and near-critical paths can be burdensome and difficult. It is not unusual for large EPC projects to contain multiple process areas represented by tens of thousands of schedule activities, which can make evaluating the critical and near-critical paths a challenging endeavor. Further, the user may be limited by the CPM scheduling program in terms of how the output of the schedule data is presented. In addition, any deficiencies in the CPM model such as open-ended activities and overuse of constraints further complicate the process.
Therefore, it is up to the schedule analyst to work within the confines of the CPM scheduling program to better organize the schedule data in a format that the project participants can understand. The purpose of this series of blog posts is to provide awareness of and discuss some of the challenges faced and steps to consider when identifying and analyzing the critical and near-critical paths.
1 See AACE® International Recommended Practice 10S-90, Cost Engineering Terminology, dated May 15, 2023, p. 39 of 134.
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