The critical path describes the sequence of tasks that would enable the project to be completed in the shortest possible time. It is based on the idea that some tasks must be completed before others can begin. A critical path diagram is a useful tool for scheduling dependencies and controlling a project. In order to identify the critical path, the length of time that each task will take must be calculated.
Let’s take a look at an example. The length of time in weeks for each key stage is estimated:
|
Key stage |
Estimated time in weeks |
|
|---|---|---|
|
A |
Secure funds |
0 |
|
B |
Negotiate with other agencies |
4 |
|
C |
Form advisory group |
4 |
|
D |
Establish data collection plan |
6 |
|
E |
Collect data |
4 |
|
F |
Write directory text |
4 |
|
G |
Identify printer |
2 |
|
H |
Agree print contract |
2 |
|
I |
Print directory |
4 |
|
J |
Agree distribution plan |
12 |
|
K |
Organize distribution |
4 |
|
L |
Distribute directory |
2 |
We have given the key stage “Secure funds” an estimated time of zero weeks because the project cannot start without the availability of some funding, although estimates would provide detail at a later stage. The stages can now be lined up to produce a network diagram that shows that there are three paths from start to finish and that the lines making up each path have a minimum duration (Figure 10.12 Critical Path Diagram ).
If we now trace each of the possible paths to “Distribute directory” (the finishing point), taking dependencies into account, the route that has the longest duration is known as the critical path. This is the minimum time in which it will be possible to complete the project.
In this example, the critical path is A–B–C–D–E–F–I–L, and the earliest completion date for the project is the sum of the estimated times for all the stages on the critical path – 28 weeks – from the point of securing the funding. All the key stages on the critical path must be completed on time if the project is to be finished on schedule.
If the projected total time is much longer than the project sponsor’s expectations, you will need to renegotiate the time scale. Mapping the critical path helps to identify the activities that need to be monitored most closely.
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