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Critical Path Method

15 Aug 2022
Critical Path Method

The critical path method was developed in the late 1950s by James E. Kelley and Morgan R. Walker. Critical Path Method (CPM) is used to estimate the minimum project duration and determine the amount of schedule flexibility on the logical network paths within the schedule model. The critical path method is a widely recognized project management technique included in the Project Management Body of Knowledge (PMBOK). PMBOK provides a standardized framework for project management practices and methodologies. It emphasizes the importance of critical path analysis in project planning, scheduling, and control.

What is the Critical Path Method in Project Management?

The critical path method involves several key steps, including defining project activities, identifying task dependencies, estimating durations, constructing the network diagram, determining the critical path, and analyzing the project schedule. The process ensures a systematic approach to project planning and enables project managers to make informed decisions as the project progresses.

Successful project delivery requires essential project management methods in all types of organisations. For example, a project in any corporation would essentially have a range of activities that need to be completed in sequence or in parallel to achieve the project goal. For timely project completion, it is vital to understand the activities involved and how they relate to each other. The critical path method is particularly valuable for managing complex projects that involve numerous interdependent tasks and a significant number of resources. In such projects, it is crucial to have a clear understanding of the critical tasks that directly impact the project's overall timeline. Critical path tasks depend on their immediate predecessors, which are tasks that must be completed before the critical path tasks can begin. Understanding the immediate predecessors is vital for accurate critical path analysis. By identifying and sequencing these tasks correctly, project managers can establish the logical flow of work and determine the project's critical path. Accurate identification of immediate predecessors is essential for creating a reliable project schedule.By identifying these critical tasks, project managers can allocate resources strategically, closely monitor their progress, and ensure timely completion of the project.

Critical path analysis involves a thorough examination of the critical path and its associated activities. By conducting this analysis, project managers gain valuable insights into the sequence and duration of critical path activities. They can identify potential bottlenecks or areas of concern, allocate additional resources if needed, and implement contingency plans to mitigate proactively address issues that could potentially delay the project completion.

For instance, consider a House Construction Project. This project would have several tasks in sequence, such as compacting the ground, forming solid bases, footing reinforcement, shuttering, footing concrete, column casting, construction of walls, masonry work to keep openings for windows, roofing, plastering work, fixing of doors and windows. Each of these tasks will require a different amount of time and resources.

Given the above example,

(1) The project consists of a defined set of activities that mark the end of the project when completed.

(2) The activities may be started and stopped independently within a given sequence.

(3) The tasks are performed in order; for example, the walls must be constructed before starting the roofing.

With the use of CPM analysis, builders can estimate the duration (hours, days, or weeks it will take to complete the task, including elapsed time), the effort (hours, days, or weeks that take to perform the actual work), and based on that they can estimate the cost or budget each task.

Accurate task identification is essential for effective critical path analysis. Project managers need to break down the project into discrete tasks and determine their dependencies. By clearly defining and sequencing the tasks, project managers can identify the critical path tasks that have the most significant impact on the project timeline. Thorough task identification lays the foundation for accurate critical path analysis and project scheduling.

Importance of Critical Path Method (CPM)

Optimum utilisation of time and resources 

 In projects, all tasks take time, but some are more time-consuming and labour-intensive than others. Therefore, it is vital to identify a precise day-to-day plan of what activities to prioritise. A critical path method is a helpful tool that facilitates task prioritisation, giving organisations a better understanding of how and where to utilise resources. In addition, it provides the team with an assessment of actual time versus planned time.

The critical path method relies on the critical path algorithm to calculate the critical path and determine the project's duration. The algorithm takes into account task dependencies, activity durations, and constraints to identify the critical path activities. Through mathematical calculations and analysis, the algorithm identifies the sequence of tasks that must be completed without delay to ensure the project's timely completion.

 The tool enables organisations to understand which tasks are taking longer than expected, which are ahead and scheduled, and which activities are right on track. The use of the tool will be helpful in terms of resource management.

 Improved planning 

 There is a risk of losing valuable time in the project process due to unanticipated bottlenecks. Certain activities must be completed in order for other activities to begin. If one person cannot start a particular activity because they're waiting on a required item to be completed, it will eventually slow down the progress. This can also create a chain of events that can put the project behind schedule. The critical path method plays a significant role in mapping out parallel tasks or activities in sequence and managing project risks that impact critical path tasks have the potential to delay the entire project. By proactively addressing and mitigating risks associated with critical path tasks, project managers can minimize the likelihood of project delays and ensure successful project completion. A thorough assessment and analysis using critical path scheduling techniques enable better time estimates.


How to find the Critical Path of Project

The following are the steps to find the critical path of the project:

1. Divide the activities of the projects

Make a list of project activities and assign each activity with a name or a shortcode.

2. Create a dependency chart.

Put the activities in a logical line-up and identify dependencies.

3. Create a network diagram

Once all of the necessary activities are divided, make a visual activity line-up visual. The network diagrams are beneficial in connecting activities in the chart.

4. Estimate activity duration

It is crucial when planning any project to calculate how long each section will take. First, clearly define the beginning and end date for each task. Then set each task's estimated duration considering the order and dependencies of the activities. Then, calculate the project completion date.

5. Determine the Critical Path

The Critical Path is the sequence of activities that represents the longest path through a project, which determines the shortest possible duration and any delay in completing activities on the critical path will delay the overall project completion. Therefore, project managers must focus their attention on managing and monitoring critical path activities to ensure the project stays on track. The work breakdown structure is a hierarchical representation of the project's deliverables, sub-deliverables, and tasks. It provides a framework for organizing and decomposing the project into manageable components. The critical path method relies on the work breakdown structure to identify the sequence of tasks and their dependencies, enabling project managers to determine the critical path and schedule the project accordingly.

6. Calculate the float

Float is the amount of time that a schedule activity can be delayed without delaying the early start date of any successor or violating a schedule constraint.

The float is determined by how long the activity takes to complete and how many days are available between the activity's start date and the one which follows directly afterward. For example, no float is available if a task takes four days to complete and only has four days available from the start to the following activity. Therefore it is a critical task.

However, float days would be available if a task only took one day to complete, but there are five days until the start of the following job.

Therefore, this task is not time critical and can be slightly delayed if necessary.

Critical Path Method Example

Let's consider a software development project as an example. The project consists of various activities such as requirement gathering, design, coding, testing, and deployment. By applying the critical path method, project managers can identify the critical tasks that directly impact the project's duration. For instance, if coding and testing activities are on the critical path, any delay in these tasks will extend the overall project completion time. By focusing resources and attention on these critical tasks, project managers can ensure timely delivery of the software.

How to use the Critical Path Method

Schedule compression

CPM is applicable in every project that determines the estimated time of interdependent activities. The method establishes a trade-off between the overall cost of the Project and the total time for completion of desired activities.

It assesses whether the estimated time could be reduced through compromising with cost (i.e. allowing the escalation of cost) or the same is not sound from a financial perspective.

CPM provides project managers with key information that allows them to minimise the project duration within certain limits by deploying additional resources at an optimal cost.

For example, if the project has some activities with negative floats, extra resources are inducted to reduce the negative float value. The process of reducing the time involved by allowing the increase in cost is known as crashing.

Initially, the normal time estimates for each activity are taken to calculate the project duration. To reduce the project duration, we need to reduce the time of critical activities because the reduction in time of any noncritical activity will not help in minimising the project duration. Therefore, the cheapest activity is selected for the crashing, and the process continues until any critical activity remains.

Measure Project Progress

A critical path schedule is useful to provide a visual representation of the critical path and the associated tasks within a project. It highlights the critical path activities, their durations, and the interdependencies between them. The critical path schedule serves as a roadmap for project managers, allowing them to track progress, identify potential delays, and make necessary adjustments to keep the project on schedule. Critical path drag is a metric used in the CPM to measure the impact of delaying a particular task on the project's overall duration. It quantifies the amount of time that a non-critical task can be delayed without affecting the project completion date. Tasks with a high critical path drag value should be closely monitored and managed to prevent any potential delays to the project.

Resource levelling

CPM can also be used for resource-levelling. Resource levelling is a resource optimisation technique in which adjustments are made to the project schedule to optimise the allocation of resources and which may affect critical path.

Resource levelling balances the demand and supply of available resources. It allows adjustments in time deadlines to meet the constraints of resources.

Resource levelling is primarily done when the restriction is on the availability of the workforce.

Levelling assists in adjusting resources against the possible floats available in the activity.

It is helpful to reduce the burden on the limited resource and establish the trade-off between the overall duration of the project and the cost involved.

Critical Path Analysis is commonly used in large industrial houses where the time involved in completing an activity can be reasonably predicted, owing to previous experiences.

A few examples of industries where CPM has wide applications are construction, defence, installation of complex equipment, engineering, aerospace, maintenance and shifting of plants, launching space programmes, traffic flow patterns, and other large projects.

Critical Path Method and PERT

A critical path diagram, also known as a network diagram or a PERT chart, visually represents the activities and their dependencies in a project. In PERT, the focus is on the start and completion of events and not activities. The activities that occur between events cannot be specified. It is appropriate for projects where the required time to complete different activities is unknown. PERT is usually applicable for scheduling, organisation, and integration of various tasks within a project. By examining the critical path analysis chart, project managers can easily identify the critical tasks and understand the flow of work throughout the project.

On the other hand, CPM is used for projects where the time needed to complete the project is already known. It helps determine the approximate time during which a project can be completed. It provides a meaningful way to keep project costs and timelines checked and balanced effectively.

Critical Path Method and Gantt chart

The Critical Path Method shows how each activity is related to one another; however, a significant problem with the Gantt method is that the Gantt charts do not show how activities relate to one another.

The critical path method represents a network diagram that displays each project activity and connects them to show task dependencies. At the same time, the Gantt chart is a bar chart that lays out project activities and timelines for each activity.

Critical Path Method: Advantages and Disadvantages

Advantages of Critical Path Method

It has the following advantages:

1. The CPM method determines the activities that can run parallel to each other.

2. The CPM helps the project managers identify the project's most critical elements.

3. CPM offers a straightforward approach to communicating project plans, schedules, time, and cost performance.

4. The CPM considers the requirements well in advance to complete a project in the most efficient way possible.

5. With the help of the CPM, the project manager can determine the duration and estimate the time and budget of the project.

6. CPM enables project managers to compare the actual progress of tasks with the project schedule. By tracking the actual start and completion dates of critical tasks, project managers can assess whether the project is on track or if adjustments are necessary. If actual progress deviates from the project schedule, project managers can take corrective actions to bring the project back on schedule.

Disadvantages of Critical Path Method

It has the following disadvantages:

1. CPM could be time consuming. It is also challenging to estimate the activity completion time in a multidimensional project.

2. The CPM networks can be complicated for extensive projects.

3. It cannot effectively tackle sudden changes in implementing the plan on the ground. For example, redrawing the entire CPM chart is extremely difficult if the project's plan suddenly changes midway.

4. CPM cannot form and control the schedules of the persons involved in the project.

5. Resource constraints can have a significant impact on the critical path and overall project duration. Limited availability of key resources, such as skilled personnel or specialized equipment, can potentially create bottlenecks and extend the critical path. Project managers must carefully consider resource constraints when planning and scheduling tasks to optimize resource allocation and minimize the impact on critical activities.