Most people seem to have knowledge of only one type of Critical Path. Moreover, what critical path really is, many have incorrect understanding about it. In this guide, I will explain the two different types of critical paths and you will also learn which one is used in what circumstance.

The two types of Critical Paths are:

1. Longest Path

This type of Critical Path comprises activities which are longest in length than other activities in the project. Longest path could be made of independent activities, in which the one with the longest duration will be critical. Alternatively, the Longest Path could be made of different set of linked activities, the set with the longest duration is Critical in this case.

You might have wondered, why longest length matters and why does that make the activity to be called critical? Well, the answer is simple. The activities with the longest length require more cost, more resources, more time. Furthermore, these activities have more combined risk, more issues. Considering all this, the longest duration activity / set of activities are called critical activities, and these are also called critical path.

You might have heard that the Critical Path determines the length of the project. Well, it is not always the case. Imagine there is an activity that is neither has a predecessor, nor does it have a longest duration, but it falls at end of the project and is independent. Hence it gives you project finish date. Since this activity is not part of activities that finish before it that includes the Critical Path, we can now not say that your Critical Path is determining the total project duration because the last project activity is not part of your Critical Path.

This type of Critical Path is not often used since it is not very important to look for those activities with more no of resources or more cost/risk/issues, etc. The more realistic type of Critical Path is the one described below and that one should always be used.

2. Activities with 0 Total Float 

This type of Critical Path does not have a name but it is formed when one or more activities have Total Float equals to 0. Before I describe this Critical Path type further, first let me explain what Total Float it

Total Float is number of days an activity can be delayed without delaying the project finish date. In other words Total Float is how much you can move activity forward without letting it cross project Finish date.

So, if your project finish date is for example 31 March and you have an activity with finish date 31 March, it's Total Float will be 0 days because it can not be moved further now. Such an activity will become critical. Now, if that activity has one or more predecessor activities, all these will automatically have Total Float 0, since if any of these moves forward, it will push the last one also, and project finish date will be moved forward.

This type of Critical Path is mostly used and is more realistic than the Longest Path. The engineers and project monitoring staff should keep an eye on activities with Total Float 0, so as to ensure these do not delay, since delay in these activities mean your project will be delayed.

Tags: Different Types of Critical Paths, Critical Path in Project Management, What is Critical Path