Class 103: CPM Scheduling
Critical Path Method
scheduling, also known as “CPM scheduling,” is a scheduling technique
that calculates the amount of time needed to complete a project using task
durations and task relationships. The
Corps of Engineers Board of Contract Appeals states that “the critical path
method of scheduling requires the logical analysis of all the individual tasks
entering into the complete job and the periodic review and reanalysis of
progress during the performance period,”1 and AACE describes CPM scheduling as
a “technique used to predict project duration by analyzing which sequence of
activities has least amount of scheduling flexibility [where 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.”2
Example of a CPM Schedule
The example above illustrates a construction schedule for a mixed-use skyscraper in which the software (Primavera P6) has used the Critical Path Method to determine the shortest feasible overall duration of the project. Each task, or activity, is connected to a series of other activities. According to CPM scheduling, there exists a particular sequence of activities in each schedule that defines the shortest amount of time needed to complete the project, which is called the critical path, shown by red bars in this example. Additionally, CPM scheduling does not disregard the other activities in the schedule; the activities that are not on the critical path can experience delay to start or finish dates without impacting the shortest possible duration of the project. These activities, represented by green bars in the example, have positive float.
CPM scheduling is an often-used scheduling practice followed in the construction industry. Most modern scheduling programs are capable of calculating and analyzing CPM schedules, which is important because most construction project schedules are too complicated to be calculated by hand. Understanding the basics of CPM scheduling enables a schedule reviewer to follow the logic in a schedule and follow the sequence of events needed to successfully complete a project.
CPM Scheduling Summary:
1. The Critical Path Method is a common method for producing construction schedules and calculating the optimal project duration.
2. CPM scheduling involves using the activity relationships and activity durations to calculate the earliest and latest start and finish dates for each activity, which then allows schedulers to determine the most efficient path through the overall project.
Key Terms:
Critical Path Method Scheduling – scheduling method that uses activity relationships and durations to calculate the earliest and latest start and finish dates for activities to determine the overall duration of the project
Activity – individual component or step of a construction schedule
Critical Path – the longest continuous sequence of activities in the schedule that determines the minimum overall project duration
Float – amount of time an activity can be delayed without impacting the overall project
Resources:
1. Jon M. Wickwire, Thomas J. Driscoll, Stephen B. Hurlbut & Mark J. Groff, Construction Scheduling: Preparation, Liability, and Claims § 2.02 (4th Edition, 2021 Cum. Supp. 2018) No. 10S-90
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