PMP?: Project Schedule - CPM - Is Critical Path Longest or Shortest? Confused??

One of the biggest misunderstandings about the critical path method (CPM) in project management is the idea that the critical path is chosen from multiple alternatives as the best or most optimal path. Many assume project managers select the critical path like picking the fastest route on a map.

This is a MISCONCEPTION. The critical path is not an alternative—it is the sequence of activities that dictates the project’s shortest possible duration. Unlike a road trip where different routes may lead to the same destination, in project management, all activities must be completed (Most probably, since the word 'path' is used, many people knowingly or unknowingly assume it to be alternatives). The critical path simply highlights the longest dependent sequence of tasks, meaning that any delay in these activities extends the entire project timeline.

To illustrate this concept, let’s look at a real-world example to understand why the critical path is not a choice but a very strong constraint that defines the project completion date.

Real-World Example: Building a Residential House

Imagine you are managing the construction of a residential house. Various activities must be completed, some of which can run in parallel, while others must follow a strict sequence.

Here’s a simplified breakdown of the key activities:

1. Foundation Work (10 days)
2. Framing (15 days, starts after foundation work)
3. Plumbing and Electrical Setup (10 days, starts after framing)
4. Roofing (8 days, starts after framing)
5. Interior Finishing (12 days, starts after plumbing and electrical setup)
6. Landscaping (6 days, can start after roofing)
7. Final Inspection (3 days, starts after all construction work is done)
8. Handover (2 days, starts after final inspection)

The following table puts the activities, durations and predecessor(s) in a simplified way:

Now, following is the network diagram for this project:

Now, let’s identify the two main paths in this project:

Path 1: Foundation → Framing → Roofing → Landscaping → Final Inspection → Handover

• Duration: 10 + 15 + 8 + 6 + 3 + 2 = 44 days

Path 2 (Critical Path): Foundation → Framing → Plumbing & Electrical → Interior Finishing → Final Inspection → Handover

• Duration: 10 + 15 + 10 + 12 + 3 + 2 = 52 days

At first glance, it may seem that the project could be completed in 44 days by following Path 1. However, this is incorrect. The project cannot be completed until all activities in both Path 1 and Path 2 are finished. Imagine, in this project what will the house have and not have if we looked at these two paths as alternatives????!!!!

Since Path 2 takes 52 days, which is longest, it is the critical path—the shortest time required to complete the project.

Why the Longest Path Determines the Shortest Possible Project Duration

It may seem counterintuitive, but the longest path determines the project’s shortest completion time for the entire project because all shorter paths run in parallel and do not affect the final project end date.

For example, in this case:

• Path 1 activities containing Roofing and Landscaping are completed in total 44 days but these 44 days overlap with 44 days contained in 52 days of the longest path.
• Even though Landscaping finishes earlier, the project cannot be handed over until the critical path activities (interior work and final inspection) are completed.

Thus, while some tasks finish earlier, the project’s completion date is controlled by Path 2, making it the critical path in this case as it is the longest. Similarly, in general, the longest path in any project will give the shortest possible duration of the entire project as the project cannot be done in less than the duration of the longest path, The other shorter paths are necessary to be completed but their activities will run parallel to the critical path and will overlap.

Why This Misconception Leads to Ineffective Project Management

1. Believing That the Critical Path is an Optional Route

Some project managers mistakenly assume they can choose a shorter path instead of following the critical path. However, all paths must be completed, and only the longest sequence of dependent tasks determines the project duration.

2. Trying to Shorten the Project by Working on Non-Critical Tasks

Efforts to reduce project duration by speeding up tasks not on the critical path will not impact the overall timeline. For example, completing landscaping faster does not change the project’s completion date if interior finishing is still ongoing.

3. Ignoring Critical Path Delays

Because any delay in the critical path directly extends the project timeline, failing to monitor it carefully can lead to unexpected schedule overruns.

Key Takeaways for PMP? Aspirants and Project Managers

1. The Critical Path is Not a Choice—It’s the Only Sequence That Defines the Project Duration since it is the longest sequence
2. Shorter Paths Exist, But They Do Not Determine the Project End Date
3. Optimizing Non-Critical Activities Will Not Reduce the Project Duration

By understanding that the critical path is not an alternative but a requirement, project managers can better plan, track, and manage project timelines, ensuring on-time and successful delivery.

Disclaimer: The residential construction project used in this article is for illustration purposes only to explain the concept of the critical path method (CPM) in project management. While the example provides a structured approach to understanding project scheduling, it is not intended to be a technically precise representation of real-world construction practices. The focus is on demonstrating how the longest sequence of dependent activities determines the project’s duration, rather than providing a detailed construction methodology.