13.4 - Critical Path Analysis
The purpose and key features of critical path analysis
Critical path analysis (CPA) serves as a planning tool to identify the most efficient sequence for completing a complex project, focusing on time management and resource allocation. It breaks down a project into individual activities, determines their sequence, and estimates durations to create a network diagram that visualises the entire process from start to finish.
How critical path analysis works
- A project consists of multiple interconnected activities that must be sequenced logically.
- Activities that can occur simultaneously are highlighted to optimise timing.
- The critical path represents the longest sequence of dependent activities with no delays, determining the minimum time needed to finish the project.
- Critical activities lie on this path; any delay in them extends the overall project duration.
- For extensive projects, software tools are often employed to build and adjust the network diagram.
- CPA supports strategic implementation by pinpointing when resources are required and allowing adjustments, such as reallocating resources to shorten the critical path.
Components of a critical path network including nodes and dummy activities
A critical path network is a diagram that maps out project activities, their dependencies, and timings. It uses arrows for activities and circles (nodes) to mark transitions between them.
Elements of nodes in a network
Each node is divided into three sections:
- Node number - A unique identifier for the point in the sequence.
- Latest finish time (LFT) - The latest time the previous activity must end to avoid delaying the project.
- Earliest start time (EST) - The soonest the next activity can begin.
If the EST and LFT in a node are identical, that node is part of the critical path.
Role of dummy activities
- Dummy activities are fictional tasks shown as dashed arrows in the network.
- They illustrate dependencies between activities without adding time or resources.
- These are essential for accurately representing complex relationships where one activity relies on another indirectly.
Calculations for start times, finish times, and float time
Various timings are calculated to manage the project effectively. These include earliest and latest times for starting and finishing activities, as well as float time for non-critical tasks.
Calculating earliest start time (EST) and earliest finish time (EFT)
EST is the earliest possible start for an activity, beginning at 0 for the first activity. For subsequent activities, EST equals the EFT of the preceding activity.
Where:
- EFT = Earliest finish time
- EST = Earliest start time
- Duration of activity = Estimated time to complete the task (e.g., in days)
Calculating latest finish time (LFT) and latest start time (LST)
LFT is the latest allowable finish time for an activity without delaying the project, starting from the final node's EST (which equals its LFT). Work backwards through the network to find LFT for earlier activities.
Where:
- LST = Latest start time
- LFT = Latest finish time
- Duration of activity = Estimated time to complete the task (e.g., in days)
Total float
Total float measures the flexibility in scheduling non-critical activities, indicating how much delay is possible without affecting the project end date.
Where:
- Total float = Time available for delays (e.g., in days)
- LFT = Latest finish time
- Duration = Estimated time to complete the activity
- EST = Earliest start time
Only activities not on the critical path have positive float time.
Worked example - Calculating total float
In a project network, an activity has an EST of 6 days, a duration of 4 days, and an LFT of 13 days. Calculate the total float for this activity.
Step 1: Identify the values
- EST = 6 days
- Duration = 4 days
- LFT = 13 days
Step 2: Apply the total float formula
Step 3: Calculate the total float
Step 4: Interpretation
This activity can be delayed by up to 3 days without impacting the overall project completion time.
Advantages and disadvantages of critical path analysis
Critical path analysis offers several benefits for project management but also has limitations that can affect its effectiveness.
Advantages of critical path analysis
- Focus on key tasks - Highlights critical activities that require careful monitoring to prevent delays.
- Resource flexibility - Allows shifting resources from activities with float time to those on the critical path to speed up completion.
- Efficient implementation - Enables different teams to begin work at their earliest start times, accelerating the overall process.
- Financial planning - Assists in predicting cash flow by scheduling when resources and payments are needed.
- Competitive edge - Determines the shortest completion time, which can provide an advantage in time-sensitive markets.
- Communication tool - Offers a clear visual representation of simultaneous tasks and dependencies.
- Systematic planning - Encourages detailed consideration of all project elements.
- Progress tracking - Allows ongoing review and adjustments to the network as the project evolves.
Disadvantages of critical path analysis
- Estimation challenges - Depends on accurate duration predictions, which may be unreliable.
- Time-consuming setup - Building and updating the network requires considerable effort.
- Pressure on quality - Strict timelines might lead to rushed work, compromising standards.
- Limited scope - Ignores cost details and quality aspects of the project.
- External risks overlooked - Fails to consider unforeseen issues like adverse weather or employee absences that could cause delays.