The critical path in project management

In project management, people often talk about the critical path. But what exactly is it? Everyone knows that in planning there are tasks and operations that must be carried out at exactly the right time as well as tasks that can tolerate a delay without jeopardising the success of the project. The critical path method is interesting because it deals precisely with the scheduling and prioritisation of project activities. Using this method is always useful and not only if your projects often take longer than originally planned.
An aerial view of a car park.


What is the critical path?

The critical path is the longest sequence of tasks, activities, and milestones on a timeline that affects the project's completion date. These tasks have no buffer time, meaning any delays will directly impact the project's duration, and they are dependent on each other. One task can only start once another is completed. When all tasks meeting these criteria are sequenced together, the minimum duration of the project is known. This requires information about individual tasks, their deadlines, and their dependencies on one another.
Example: A four-story building is being constructed. The first floor can only be built after completing the ground floor's ceiling. The roof can only be placed on the building after all exterior walls are in place. This is, of course, a simplified explanation, but it illustrates the concept of the critical path quite well. In contrast to these critical tasks, a non-critical task would be, for instance, creating a flowerbed next to the building. This task can begin independently and can still be completed on time. The flowerbed doesn't have to wait for the first or fourth floor to be completed. It can start when, for example, the walls are not yet entirely finished. On the other hand, the roof must wait until the exterior walls are finished. Any delay in the completion of the exterior walls will postpone the start of roofing work and thus affect the completion date.
There are several ways to manage this critical path, including using Gantt charts and network diagrams.

How to recognize the critical path

The network diagram provides a clear representation of processes and activities and their interdependencies. These activities can be work packages or smaller units that are visualised in the network diagram according to their chronological sequence. Based on the network diagram, communication tools can be developed to support the project efficiently. An important project control tool is the critical path, which can be identified in the network plan as it contains the activities that have no buffer time and require the most time.
The network diagram is based on the work breakdown structure with its work packages. These work packages describe the activities required to complete specific tasks. The first question is which work packages are necessary and how they are related to each other, i.e., what dependencies exist. Some activities cannot begin until others have been completed, while others can be carried out in parallel. To illustrate these relationships, the work breakdown structure is transformed into a network diagram. Each activity is assigned information, such as the duration of the activity. This duration is determined by the earliest/latest start date and the earliest/latest finish date. To determine the critical path and buffer times, forward and backward calculations are required. Either the earliest start/end dates for all activities or the latest reference dates are calculated. The critical path represents those activities where the earliest and latest start and finish dates coincide, and no buffer times are available.
In addition to the network diagram, the use of a Gantt chart is recommended. In a Gantt chart, all tasks are considered, and it is decided which tasks build on each other. As an example, consider the construction of a house: The walls cannot be built until the foundation is in place. The foundation cannot be poured until the excavation has been completed. The lamps, on the other hand, can be selected and ordered at any time without other tasks having to be completed. A well-designed Gantt chart shows the critical path at a glance. Tasks that build on each other are displayed side by side on a timeline without overlap. The other project steps can be grouped around this line. It is important to ensure that a task on the critical path is never moved to create space for a non-critical task.

Why is the critical path important?

The timely completion of activities on the critical path is crucial, otherwise the project duration is jeopardised and automatically extended. The method identifies bottlenecks in the project and, if identified in time, countermeasures can be taken.
As mentioned earlier, the forward and backward calculations also take into account the buffer time. This float represents the time flexibility of an activity - it indicates how long an activity can be delayed without jeopardising the deadline. Activities with a buffer time are not part of the critical path and can be moved to a later date if time or resources are tight. This also has a positive effect on risk management, as it allows you to focus on the activities on the critical path.
Two techniques can be used to deal with schedule slippage: "fast tracking", to identify activities that can be done in parallel to save time, and "crashing", where more resources are allocated to an activity to speed it up. For example, additional staff may be requested, or the existing team may need to work longer hours. It is important to have sufficient resources available without causing disruption elsewhere.
The network diagram allows a systematic consideration of the project's interrelationships to achieve reliable scheduling of activities. Potential slack and bottlenecks become visible. Through controlled and monitored project scheduling, resources can be optimally utilised.


The critical path can be used to identify those activities in the project where delays are particularly risky and where countermeasures need to be taken from the outset. They should be monitored closely. If necessary, it is also possible to save time on the critical path and thus shorten the overall project, i.e., stay under schedule. 
As described above, there are several ways to define the critical path. It is up to the project manager to find the one that works best for them. 
It can be said that the critical path is a useful tool for planning a project successfully so that the schedule can be kept well.

Critical path - the IAPM logo
Author: IAPM internal
Keywords: Project management, Critical path

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