When planning a project, the question of leeway arises. Knowledge of the critical path is essential …
Definition of the critical path
When constructing a PERT diagram (a method of scheduling tasks in a project), the critical path represents the sequence of tasks that has no slack: that is, it does not there is no flexibility between the previous task and the next. This plot indicates the incompressible timeframe for carrying out the project.
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What is the point of the critical path?
It is important to identify this critical path because it is an element of forward-looking management that makes it possible to master key stages and deadlines. It is a central tool for the implementation of a PERT. The final step for the project manager is to have an effective and relevant planning tool. The identification and layout of the critical path allow in particular:
identify the levers for reducing delays: knowledge of the critical chain makes it possible to identify the priority tasks on which to act if one wishes to reduce the duration of the project planning as a whole. It is then possible to take the necessary measures to act: allocation of resources (staff, budget, etc.), shifting of deliverables (while respecting the objectives of the project), etc.
prevent slippage and control risks: these same tasks must be closely monitored to prevent deadlines from slipping due to delays in these critical tasks. It is a valuable tool for identifying as early as possible the hazards (and overdue tasks) that can delay the project, activities that cannot be completed within the required time.
evaluate scenarios: it is relevant to test different combinations on a timescale (sequence of tasks and content of steps) to analyze the impacts over the duration of the project by identifying the project margins and each critical path. The consequences are then directly apprehensible on the planning.
Project management tools (project management software such as MS-project) greatly facilitate the creation of a network diagram (identification of prior art, dependencies between tasks, etc.). The automatic construction allows the critical path to be displayed and helps to develop alternatives with the aim of completing the project as soon as possible. The flexibility of the tool offers the opportunity to perform simulations, observe several critical paths according to input variables.
Building the Gantt chart is the final step after establishing the critical path. From the first works to the end of the project, each step is set on a schedule. Each milestone is visible.
How to reduce the duration of the critical path?
When the project requires a faster delivery of deliverables than that imposed by the critical path, project managers have 2 main options at their disposal.
Bring additional resources to critical path tasks: more staff, outsourcing of certain activities, etc. Provided that these additional resources really make it possible to shorten their duration and that these resources can be mobilized. The consequence is the inflation of the cost of the project compared to the initial budget.
Process tasks in parallel when they had to be chained. This involves starting an activity earlier than planned without waiting for the end of the previous one on which it depends – for example: starting work before the specifications are finalized, starting the construction of a prototype without the study being completely finished, etc. In this situation, it is necessary to assess two types of risk: the quality risk, where this change of organization can generate a lower level of quality than what was expected – and financial risk, in particular, if the anticipated task takes the wrong one. direction and that it is necessary to start over in whole or in part, or to modify certain points with, again, a quality risk.
What is the Critical Path Method?
Beyond the critical path used in the PERT method, there is an approach called the “Critical Path Method” (CPM). It is described in particular in the PMBOK, (project management repository).
Unlike PERT, the activity is registered in the node (and not the arrow – or bow – which connects 2 nodes or boxes). Each node (also called “vertex”) includes this information:
Like PERT, this approach is also attached to calculating existing margins to prevent and manage lags:
Total margin = DTA – DTO or FTA – FTO
For the English version:
Early start = ES = Early Start
Early Finish = EF = Early Finish
Latest start = LS = Late Start
End at the latest = LF = Late Finish
See also the “Critical Chain Method” (CCM), the objective of which is to add “buffers” on one or more chains, at the level of resources and at the end of the project. These “buffers” are buffer zones allowing flexibility to be provided by improving the project margin. Make it more agile, release tensions and constraints to absorb hazards while maintaining pressure on each task