Critical Path

The critical path is the longest sequence of tasks in a project. The tasks on the critical path control the duration of the entire project. Any increase in duration of a critical path task will always cause the project’s duration to increase. The Critical Path is a great tool to help you shorten the duration of your project and plan corrective action. It lets you focus your attention on the tasks where adding resources will allow the project to finish early. Most project management software automatically calculates the critical path if you set up the schedule properly. That means you don’t enter start and finish dates. Instead, you use estimates of the amount of work and predecessor relationships between the tasks. This requires a little extra effort in the beginning but it gives you the critical path method for the life of the project. Project Schedule & Software Main Page

Dick Billows, PMP

Dick Billows, PMP
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Use the Critical Path to Crash the Plan

You should use critical path analysis to optimize the project schedule.  First you examine each of the tasks on the critical path, looking at the resources they are utilizing. You can shorten your critical path by adding resources to these critical path tasks. That’s called crashing the plan.

As you add these resources,  the critical path can change. Although the critical path is the longest path, there are always several paths through the project. As you shorten your critical path, its duration will decrease. After you add resources, a different sequence of tasks often becomes the critical path.  That’s why most project software is continually calculating the critical path. It identifies the tasks that are on it, usually by coloring them red. After your critical path has changed, you examine those tasks for opportunities to add resources to shorten the tasks’ duration and, thus, the project’s duration. Remember that you gain nothing by adding resources to noncritical path tasks.

Use the Critical Path to Fast Track the Plan 

You can also change the duration of the critical path by altering the predecessor relationships between the tasks. You look at the tasks on your critical path and focus on those that have a finish-to-start predecessor relationship. For example, task A and task B have a finish-to-start relationship if task A must finish before task B can start. Some tasks must have finish-to-start predecessors. If work breakdownyou are building a house, for example, the foundation (task A) must be dry before you can start building the walls (task B). But there are some tasks where you can alter the pure finish-to-start predecessor relationship. You can start the second task a few weeks earlier than the pure finish-to-start predecessor would allow. An example is a design task (task A) followed by a construction task (task B). You might be able to begin the construction task (task B) before the design task (task A) is totally complete. Once again, you would only do this on critical path tasks so that the fast tracking change will shorten the project’s critical path.

Use the Critical Path for Trade-offs

Whenever the project sponsor talks with you about finishing earlier (and that may happen weekly), you can use the critical path and your project software to model options.  If the sponsor asks about finishing 10 days earlier, you would use your critical path and schedule software to calculate how many more resources you need to do that. You would examine your critical path tasks and focus on the longer ones because you want to gain 10 days of duration. If you found task #31 on the critical path and it was currently scheduled for a 20 day duration (4 weeks), you might look at it more closely. If that task had one engineer doing 160 hours of work, you might model an option of adding a second engineer and spreading the work between two people. That should come close to reducing the 20 day duration to 10 days or so. Then you could offer the sponsor a trade-off off by saying, “If you give me a second engineer for task #31 for two weeks, I can cut the duration by 10 days.”

Use the Critical Path for Change Requests

Every project manager has to deal with requests to change the project finish date, the budget or the scope. These “requests” come from people who outrank you or sign your paychecks. You can use the critical path method to assess the trade-offs between the various dimensions of the project. Then you can present options to the sponsor and stakeholders for changing the project’s scope, duration, cost or risk to better fit their requirements. It’s wise to go into meetings with options for those changes already modeled so you can present them when someone asks. You’ll have the data available to tell them what the scope change will cost in terms of increased budget and increased duration. The best technique is to use trade-offs between the project’s dimensions, the “4 corners” of scope, duration, cost and risk, to handle the change request and maintain the project’s feasibility.

Critical Path Requirements 

You use trade-offs analysis between scope, duration, cost and risk during planning, during each week’s status meeting, and on all change requests/change orders. The critical path technique helps you calculate them. You can:

  • Decide which problems you have to solve and which you can safely ignore
  • Find the cheapest way to shorten the duration of the project
  • Assign your best people to the tasks that control the project’s duration.

So why don’t more project managers use the critical path methop? Because it requires you to use the following scheduling techniques:

  1. You must base durations on availability and work (i.e., a task with 12 hours of work for a half-time person takes 3 days’ duration)
  2. You must use predecessor relationships to control task sequencing (i.e., start-to-finish or finish-to-finish) rather than entering start and finish dates.

Those two techniques are the foundation for critical path analysis. They will save you hours of work because your schedule will dynamically update. That makes learning them worth learning. In the picture below, the tasks in red are on the critical path, the longest sequence of tasks. The tasks in blue are not on the critical path.


critical path

Critical Path in the Software

Notice how the sequence (or path) of red tasks takes longer than the other paths. Now look at the blue tasks that run from row #14 – Row #25.  They finish almost a month before the red tasks on the critical path. How could you use that information?  Remember that if any of those blue tasks finish a little bit later than planned, it’s not going to increase the overall duration of the project.  So if you want to shorten the duration of the project, you could take resources off some of those blue tasks (which would make them take longer) and have them work on a critical path task. That’s one way to shorten the duration of your project and you should model that option in the software. An added bonus is that when you can identify that kind of opportunity, shortening the duration doesn’t increase the project’s costs.

Another way you can use the critical path is to decide how serious a problem is. As an example, if the person working on task #18 tells you they made an incorrect estimate and their task is going to take five days longer than planned, should you become hysterical?  No. A quick look at the critical path information shows you that task #18 can finish weeks later than its current scheduled completion date without affecting the duration of the project. Consistently successful project managers have information that lets them decide which schedule variations they have to solve and which ones they can accept. That saves a lot of wear and tear on you and the project team.

Using these critical path techniques save you time and give you information to make better decisions about your projects.  We cover these critical path tools and techniques in all our customized, personal online training courses. You will work individually with an expert PM and learn how to optimize schedules so the project finishes as soon as possible.  You’ll also learn to present the project stakeholders with trade-off options based on your critical path analysis. You work privately, 1-to-1, with a expert project manager. You control the schedule and pace and have as many phone calls and live video conferences as you wish.  Take a look at the courses in your specialty.

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