A Project Management Primer – Basic Principles – The Critical Path
A Project Management Primer – Basic Principles – The Critical Path (#3 in the Hut A Project Management Primer)
By Nick Jenkins
Another important concept in planning projects is that of the critical path. If a project consists of a set of tasks which need to be completed, the critical path represents the minimum such set, the critical set. This might seem to be a contradiction since you might think completion of all tasks is necessary to complete a project; after all, if they weren’t necessary they wouldn’t be part of your project, would they?
The critical path represents not the ideal set of tasks to be complete for your project, but the minimum set. It is this path that you must traverse in order to reach completion of your project on time. Other tasks while important to overall completion do not impact upon the final delivery for the project. They can therefore be rescheduled if time is tight or circumstances change. Tasks on your critical path however will affect the delivery time of the project and therefore should only be modified in extremis.
In the following example the critical path is represented in bold. In order to complete my project of cooking breakfast I have to go through the steps of frying bacon and sausages and scrambling eggs.
The tasks “make toast” and “wash plates”, while important, are not time-dependent or as critical as the other three tasks. I can move either of those tasks but if I try to move anything on the critical path its going to delay the project.
Ideally I’d like to have toast with my breakfast but a) it’s not essential and b) it doesn’t matter where in the process it happens. If I make toast before or after scrambling my bacon, it makes little difference to the overall result.
On the other hand I can hardly fry my bacon before the oil is hot, nor can I scramble my eggs before frying my bacon (they’d turn to glue).
The critical path represents the critical sequence of events which must occur if I want to successfully complete my project.
Normally major ‘milestones’ will be represented on the critical path and they will often occur when different threads of the project come together.
For example in the diagram to the right my only milestone is when I serve the completed breakfast. At this point I will have finished my preparations and completed everything on both tracks. This is represented by a diamond in the diagram above.
If I suddenly discovered I was late for work, I could cheerfully discard the optional “toast” component of my project, take the critical path instead and still achieve my original milestone of delivering breakfast (and maybe even make it to work on time!).
Next in the Hut A Project Management Primer:
A Project Management Primer – Basic Principles – The Mythical Man Month
Previously in the Hut A Project Management Primer:
A Project Management Primer – Basic Principles – Scope Triangle
Nick Jenkins is an IT manager with 10 years experience in software development, project management and software testing. He’s worked in various fields of IT development in Australia, Britain and the USA and occasionally he learned something along the way. Now he lives on the banks of the Swan River in Perth, Western Australia, and he publishes the odd guide to help aspiring IT professionals. Nick’s website can be found at www.nickjenkins.net.
Unfortunately this understanding of what “critical path” means is a common one, and not correct.
In planning a project all the main tasks are determined, their interdependencies set, and effort or duration established. If we wanted to draw a line from start to finish – as though through a maze – there would be many possible paths. The critical path is the path that takes the longest time. It represents the tasks that have the least slack in their start or delivery dates. It does NOT have anything at all to do with a task’s Importance to the project. The word ‘critical’ is about the path.
Unfortunately the example is also a poor one because ‘scramble eggs’ can overlap with the end of ‘fry bacon’ etc; ‘wash plates’ as a step must come after serve (unless there are no clean plates); and decisions (the diamond shape) are not critical path components.