Critical Path : Why is it Important

What is critical path?

Critical path method is a process that :

CPM includes:

Why is critical path so important?

Using these values, CPM usually calculates the longest path of planned activities to the end of the project, and the earliest and latest points that each activity can start and finish without making the project longer. This process determines which activities are "critical" (i.e., on the longest path) and which have "total float" (i.e., can be delayed without making the project longer).

The critical path consists of the longest sequence of activities from project start to end that should be started and completed exactly as scheduled to ensure the project is completed by a certain date in the future. The activities on the critical path must be very closely managed. If jobs on the critical path slip, immediate action should be taken to get the project back on schedule. Otherwise, completion of the whole project will slip. Imagine that you have a project that will take 300 days to complete. If the first activity on the critical path is one day late, the project will take 301 days to complete, unless another activity on the critical path can be completed one day earlier. So the critical path is simply all the tasks that determine the end date in your project schedule.

There can be more than one critical path in one project, so that several paths run in parallel. For instance, in our case, “choose a picture” and “hang the picture,” as well as “buy the screws,” “screw in the screws” and “hang the picture” form other task sequences that also are important for us to complete the project.

The critical path may contain all the important activities on the project, or it may not. In fact, sometimes the activities on the critical path are not the most important parts of the project. At the same time, there will be tasks that are not on the critical path, but still determine your project’s success. Understanding the critical path involves determining which activities are critical to complete on time. But other activities, lying outside of critical path, also may be very important and require extra diligence and focus.

How to find the critical path?

Step 1: Identify the activities
Step 2: Sequence the activities
Step 3 : Draw a network diagram
Step 4:Estimate completion time for each activity
Step 5:Identify the longest path
Step 6: Update the CPM diagram as the project progresses

Example

Let’s take a simple, real-life project: hanging a picture on the wall. What should you do to complete this mini-project successfully? First, we need to define and list all the tasks that have to be done, so that the whole project is completed.

Choose a place on the wall

Buy the screws

Choose the picture

Drill a hole

Screw in the screws

Hang the picture

When we think of these tasks, we realize that some of them cannot start before the others are finished. That is, some tasks are dependent on the others.

When we think of these tasks, we realize that some of them cannot start before the others are finished. That is, some tasks are dependent on the others.

The actions “drill a hole,” “screw in the screws” and “hang the picture” form a sequence of tasks that must be performed in a specific order, one right after the other, to ensure a successful result. Such tasks are called “sequential” activities.

So these three tasks, together with the start of our project (“choosing a place on the wall”) in our example, are the most important critical steps that must be taken to arrive at the proper solution to our problem. These actions will be placed on your critical path for this project. So the essential concept behind Critical Path Analysis is that you cannot start some activities until the others are finished. These activities need to be completed in a sequence, with each stage being more-or-less completed before the next stage can begin.

Now.let us create the schedule for this, it looks something like:

Limitations

• CPM is not suitable if projects cannot be broken down into discrete activities with known completion times. For example, on a new project, activity durations may be hard to estimate.
• Critics note that it takes too much time to identify all activities and inter-relate them to get multiple project paths. This causes user frustration ahead of the project.
• PM stops working in practical situations in which employees are often re-allocated across projects and activities. This reallocation changes activity completion time and disrupts the CPM plan.
• Identifying a single critical path is difficult when there are parallel paths with similar durations. Project teams may disagree on which path to choose or which activities are more critical than others.