Managing critical project paths is a challenge for all project managers. In fact, in every project, you can have hundreds of tasks with dozens of dependencies and interdependencies.
Although all useful, not all tasks will have a decisive impact on the project. Therefore, it can become very difficult to identify the most important tasks, those that, if not considered adequately, will have an impact on the whole project.
In other words, let’s talk about the tasks you really need to worry about (and that will therefore be part of critical paths) in order to make sure you meet deadlines and critical tasks and activities.
The critical path method is a project management technique created in the 50s, which allows us to identify the important tasks and to keep the project on track.
Starting from hand-drawn diagrams and evolving to automated software, the critical path method has become an essential part of a project planning.
The critical path method, also called CPM, is a project management technique for process planning. It defines critical activities, and not, with the aim of preventing problems during the entire life cycle of the project.
The CPM is ideal for projects consisting of many activities that interact with each other in a complex way.
In applying the CPM, there are several steps that can be summarized as follows:
- Define the required tasks and enter them in a sorted, sequential list.
- Create a flowchart or another diagram that shows each activity in relation to the others.
- Identify critical and non-critical relationships and paths between activities.
- Determine expected completion or execution time for each activity.
- Identify or process alternatives for the most critical routes.
What is the CPM method?
The concept of CPM is quite simple and can best be illustrated with a project graph.
The graph of the project is useful as a means to represent, visually and clearly, the whole interrelations and dependencies.
First of all, every work necessary for the completion of a project is listed with a unique symbol, such as a letter or number, the time needed to complete the task and its prerequisites.
For convenience, in the graphical representation and as a control of certain types of errors in the data, the activities can be represented only when all the previous ones have been listed. In concrete, work A precedes B, B precedes C and C precedes A.
Each activity is drawn on the chart as a circle, with its identification symbol and time, which appears inside the circle.
Sequence relations are indicated by arrows that connect each circle / activity with those immediately following, with the arrows pointing to the latter.
For convenience, all circles / activities without predecessors are connected to a circle marked as “Start”; while all the circles / activities without successors are connected to a circle marked as “End”.
The “Start” and “End” circles can be considered as zero-duration activities.
Generally, the graph depicts different “arrow paths” from Start to End. The time required to cross each route is the sum of the times associated with all the activities in that route.
The critical path is therefore the longest path, in time, from the “Start” circle to the “End” circle and indicates the minimum time necessary to complete the entire project.
Only by finding ways to reduce tasks along the critical path, you can reduce the overall project time. The time required to perform non-critical work is in fact irrelevant from the point of view of total project time.
On average, only around 10% of tasks in large projects are crucial.
Of course, if one finds a way to shorten one or more of the critical activites, not only will the entire project time be shortened, but the critical path itself may shift and some previously uncritical activities could become critical.
The first 3 key steps in the critical path method
1) Specify each activity
Using the Work Breakdown Structure or WBS, it is necessary to identify each activity involved in the project .
This list of specific activities should only include activities of a higher level, a generic one.
When too detailed activities are used, critical path analysis can become too complex to manage and maintain.
A WBS then subdivides the project into manageable sections.
The first step is to identify the main results of a project and from here start to divide the activities into smaller and more detailed blocks of work.
You can choose how to display a structure for decomposing the work; some people use a tree structure, while others use lists or tables.
2) Establishing dependencies or sequences of activities
Some activities will depend on the completion of others.
The list of immediate predecessors of each activity will help to identify the correct order.
To correctly identify the activities and their precedence, the following three questions must be asked for each activity derived from the first step:
- What activity should take place before this activity takes place?
- Which activities must be completed at the same time as this activity?
- What activities should take place immediately after this activity?
3) Draw the diagram
Once the activities and their dependencies have been identified, it is possible to trace the analysis graph of the critical path, known as a network diagram.
The network diagram is a visual representation of the order of activities based on dependencies.
The other key steps in the critical path method
4) Estimation of the time of completion of the activity
Using the past experience or the knowledge of an experienced team member, it is necessary to evaluate the time needed to complete each activity.
You can use the three-point estimation method, or PERT, designed to give more weight at the most realistic time period.
In the three-point estimate, it is necessary to elaborate three time estimates for each activity, based on previous experience or the best hypotheses.
This method presents formulas to calculate the time duration more accurately:
- a = the best estimate
- m = the most probable estimate
- b = the worst estimate
These three values identify what happens in an optimal state, what is most likely, and what happens in the worst case scenario.
Once you have identified these values, you can use them in different formulas.
5) Identify the critical path
By looking at the diagram and simply identifying the longest path in the entire network, the critical path will be identified, ie the longest sequence of activities on the path.
Make sure you look for the longest route in terms of duration, not the route with the most activities in it.
6) Update the critical path diagram based on progress
As the project progresses, the actual time to complete the activity will be known.
The network diagram can then be updated including this information, instead of continuing to use the estimates.
With the update of the diagram once new information has emerged, a different critical path can be recalculated.
You will also have a more realistic view of the completion date of the project and you will be able to tell if the project is on line or behind the initial planning.
Benefits and limitations of the critical path method
Like any method, even the critical path has advantages and disadvantages.
Following are some advantages of the critical path method:
- Graphic view of the project.
- Discovers and makes dependencies visible.
- Helps in planning, scheduling and project control.
- Helps in emergency planning and risk management.
- Shows the critical path and identifies critical activities that require particular attention, highlighting the overall duration, as well as the end of the project.
- Shows where to act in order to bring the project back on track.
Although the critical path is a very useful tool in planning the project, it also has some limitations and some drawbacks:
- Because the critical path method is an optimal planning tool, it always assumes that all resources are available for the project at all times.
- It does not consider resource dependencies.
- Pays less attention to a series of non-critical activities, even if sometimes they can become critical ones.
- Critical path-based projects are often not completed within the approved duration.
To conclude, the critical path method has helped many project managers to develop and manage their program.
In the critical path method, the path with the longest duration is known as a critical path.
During the execution of the project, the main emphasis will be on this path.
As a project manager you will have to keep an eye on the network diagram and take prompt corrective action whenever necessary.