Critical Path Analysis

This section explains critical path analysis covering, the nature and purpose of critical path analysis, how to complete and interpret simple networks to identify the critical path, how to calculate the earliest start time (EST), latest finish time (LFT), and total float, and the limitations of using critical path analysis.

Critical Path Analysis (CPA) is a project management tool that helps businesses plan and manage projects by identifying the most important tasks and the minimum amount of time required to complete the project. It is used to ensure that a project is completed on time and within budget by focusing on critical tasks that must be completed in sequence.

In this section, we will explore the nature and purpose of Critical Path Analysis, how to complete and interpret simple networks to identify the critical path, how to calculate key project timings such as Earliest Start Time (EST), Latest Finish Time (LFT), and total float, and finally, the limitations of using CPA.

Nature and Purpose of Critical Path Analysis

Critical Path Analysis (CPA) is used to determine the longest sequence of activities in a project that must be completed for the project to be finished. This sequence is known as the critical path. The activities on the critical path are crucial because any delay in these tasks will delay the overall project.

The purpose of CPA is to:

1. Identify the Critical Path: The critical path shows the shortest possible time required to complete the project. Any delays in the tasks on the critical path will directly delay the entire project.
2. Determine Project Times: CPA helps calculate the Earliest Start Time (EST), Latest Finish Time (LFT), and total float for each task, helping managers identify flexibility in scheduling and allocate resources efficiently.
3. Allocate Resources Effectively: By identifying the critical tasks, CPA allows businesses to allocate resources (such as labour, equipment, or money) to tasks that will have the most significant impact on the project’s overall duration.
4. Manage Project Risks: By understanding the dependencies between tasks and the critical path, businesses can anticipate potential risks and plan for mitigation strategies if delays occur.

Complete and Interpret Simple Networks to Identify the Critical Path

A network diagram is a visual representation of the project’s activities and their dependencies. Tasks are represented as nodes (usually circles or rectangles), and dependencies between tasks are represented as arrows connecting the nodes. By completing and interpreting simple networks, businesses can identify the critical path, which is the longest path from the start of the project to the finish.

Example of a Simple Network Diagram

Consider the following project with five tasks:

• A: Start
• B: Task 1 (2 days)
• C: Task 2 (4 days)
• D: Task 3 (3 days)
• E: Task 4 (5 days)
• F: Finish

The tasks and their dependencies are as follows:

• B must be completed before C.
• C must be completed before D.
• D must be completed before E.

The network diagram would look like this:

Start → B → C → D → E → Finish

                (2) (4) (3) (5)

Identifying the Critical Path

To identify the critical path, we calculate the total duration of each path from start to finish:

1. Path 1: Start → B → C → D → E → Finish
   Total duration = 2 + 4 + 3 + 5 = 14 days
2. Path 2: Start → B → C → D → E → Finish
   This is the same path as Path 1, and thus the critical path is 14 days.

The critical path is the path that determines the project’s overall duration, which in this case is 14 days.

Calculate: Earliest Start Time (EST), Latest Finish Time (LFT), and Total Float

Once the critical path has been identified, it is important to calculate key project timings to assess flexibility and optimise project scheduling.

Earliest Start Time (EST)

The Earliest Start Time is the earliest possible time that a task can start, given the task dependencies. The Earliest Start Time of the first task is always 0 (assuming the project starts immediately).

To calculate the EST for subsequent tasks, we add the duration of the preceding task to its EST.

Latest Finish Time (LFT)

The Latest Finish Time is the latest possible time a task can be completed without delaying the overall project. The LFT of the final task is the same as the total project duration (as determined by the critical path).

To calculate the LFT for other tasks, subtract the duration of the following task from its LFT.

Total Float

The total float (or slack) refers to the amount of time a task can be delayed without delaying the overall project. Tasks on the critical path will have zero float, meaning any delay will result in a project delay.

Total Float Formula:

$$\text{Total Float} = \text{LFT} - \text{EST} - \text{Duration of Task}$$ 

Example Calculation

Using the previous network example with the critical path of 14 days, let’s calculate the EST, LFT, and total float for the tasks.

Total Float Calculation:

• Task A has no float because it is the start task.
• Task B, C, D, and E all have zero float because they are part of the critical path.

If any task along this path were delayed, it would delay the entire project.

Limitations of Using Critical Path Analysis

While Critical Path Analysis is a useful tool for project management, it does have several limitations:

Assumes Certainty in Task Durations

• CPA assumes that task durations are known and fixed. However, in reality, task durations are often estimates, and unforeseen delays or complications can affect the accuracy of the schedule. This assumption of certainty can make CPA less reliable in volatile environments.

Complexity for Large Projects

• For very large projects with many tasks and dependencies, constructing and maintaining the network diagram can become very complex. In such cases, the calculations and identification of the critical path may require a lot of time and effort, making CPA less practical.

Doesn’t Account for Resource Constraints

• CPA focuses solely on the time aspects of a project and does not take into account resource constraints (e.g., availability of staff, materials, or equipment). This can lead to unrealistic project schedules if resource limitations are not considered.

Ignores External Factors

• CPA is a tool for planning within the project itself but doesn’t consider external factors such as market changes, regulatory delays, or environmental issues, which could also affect project timelines.

Static Approach

• Once the critical path is identified, the analysis doesn’t account for changes that may occur during the project. If new tasks are added, or if the project's scope changes, the critical path needs to be updated, which can be time-consuming.

Does Not Address Risk

• CPA does not directly address project risks or uncertainties. Although it identifies the critical path, it does not account for the likelihood of delays or disruptions that may impact those tasks.

Summary

Critical Path Analysis is a powerful tool for project management, helping businesses plan and manage projects more effectively. By identifying the critical path, calculating key timings such as Earliest Start Time (EST), Latest Finish Time (LFT), and total float, businesses can optimise resource allocation and ensure timely project completion. However, it is important to recognise the limitations of CPA, including its assumptions about certainty, complexity for large projects, and failure to account for resource constraints and external factors. Therefore, while CPA is valuable, it should be used in conjunction with other project management techniques and strategies.