Lessons Learned: Critical Path Method Scheduling

By: John Dillon

Through experience that spans every major area of construction, we have gained valuable insight on how to best utilize CPM scheduling to effectively manage a construction project—particularly in situations where a project results in a multimillion-dollar dispute.

While some items below may seem trivial, and this is not an all-inclusive list, each is a real issue that could be a significant factor in the ability to properly execute a project, not to mention the ability to efficiently perform a retrospective CPM schedule analysis. The bulleted items are written primarily from a contractor’s vantage point, but they can easily be reconfigured from the owner’s view, with respect to what the contractor should do in terms of its scheduling practices.

Do

  • Be sure that your CPM schedule and associated practices conform to contract requirements.
  • Perform periodic progress updates and maintain a consistent interval (i.e., monthly).
    • For each update, archive the prior update before inputting new progress (status).
    • Save each update with a unique file name that identifies that number and/or date of the update.
  • Maintain a tabular Schedule Index that documents each update, showing key statistics such as the file name, data date, number of activities, forecasted project end date, and forecasted dates for other key milestones.
  • Use industry-common terminology. For example, the “Baseline” schedule should refer to the first schedule, which is typically the one that is in the contract. Periodic updates should be called just that (i.e., “the 31Jan13 Periodic Update” or “the 31Jan13 Status Update”).

Don’t

  • Do not utilize intermediate constraints throughout the project. In general, one constraint should be used within the project schedule: a Late Finish constraint on the final project finish milestone. This will allow for proper calculation of an accurate “cradle to grave” critical path.
  • Do not leave activities “open-ended”—translation: make sure that every activity has appropriate logic ties (i.e., predecessor(s) and successor(s) activities) in order to create and maintain a schedule that has a fully robust network.
  • Avoid using excessive lags with the schedule logic (i.e., Finish-to-Start + 200 days).
  • Do not “overthink the schedule.” Maintain a realistic activity count. For example, in most cases, a large industrial construction project typically requires a schedule somewhere in the magnitude of 5,000 to 10,000 activities. A schedule with an activity count that is significantly larger than this range often escalates into a schedule that is too cumbersome to manage effectively.

The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of Berkeley Research Group, LLC.