Critical Path Method

Project Management

Critical Path Method

• Scheduling and Project Management tool developed in the 1950’s• Allow us to plan all tasks which must be completed in a project• Aids time scheduling and resource planning• They allow progress towards project goals to be tracked

Using the Critical Path Method• Some activities cannot be started until previous activities have been

completed• Activities in a critical path method therefore need to be completed in

sequence• These activities are known as sequential activities• In addition to these activities there are tasks which can be completed

at any time• These activities are known as non-dependent or parallel tasks

Drawing a Critical Path Method Chart

Step 1:• List all the tasks needed for the project in the plan• This can be done using a Work Breakdown StructureFor each task state:• The earliest start date• The estimated time it will take

Drawing a Critical Path Method Chart

Step 2:• Establish whether the activity is sequential or parallel• For sequential tasks dependant tasks should be highlighted

Establish sequence by looking at:

• Which tasks should take place before this task happens.

• Which tasks should be completed at the same time as this task.

• Which tasks should happen immediately after this task.

Drawing a Critical Path Method Chart

Step 3:• Draw each task as part of a circle and arrow diagram• Each circle or node should show a task within the project and give start and finish

times• The circles are numbered to allow them to be easily identifiable • The arrows or arcs which run from circle to circle show the activities needed to

complete the tasks• A description of the task should be written under the arrow, with the duration of

the task written above it. • Arrows always run left to right

Examples of Critical Path Method

Drawing a Critical Method ChartStep 4:• Identify the critical path • This is done by determining the four parameters of each task in the network • Earliest start time (ES) - The earliest time an activity can start once the previous dependent activities

are over.• Earliest finish time (EF) - ES + activity duration.• Latest finish time (LF) - The latest time an activity can finish without delaying the project.• Latest start time (LS) - LF - activity duration.• The float time for an activity is the time between the earliest (ES) and the latest (LS) start time or

between the earliest (EF) and latest (LF) finish times.• During the float time, an activity can be delayed without delaying the project finish date.• The activities in the critical path have an effect on the deadline of the project. • If an activity of this path is delayed, the project will be delayed.

Benefits of the Critical Path Method

The benefits of CPM are:

• Visual representation• The project plan can be tested to ensure it is well thought out• It identifies key tasks which could cause delays to the project if not completed on time• It identifies tasks which could be delayed in order to complete other tasks which are

more time crucial • It identifies the minimum amount of time a project will take to complete• It identifies any project steps which can be completed faster in order to complete the

project on time

Disadvantages of Critical Path Method

The disadvantages of CPM are:

• Can be more difficult to understand than Gantt Charts• The time needed for tasks is not as clear as with Gantt Charts

More Information on Critical Path Method• This is a useful video which sums the information given in the slides

and will aid understanding of the critical path method

http://www.youtube.com/watch?v=SF53ZZsP4ik

Further Reading

• Kelley, J. E. (1963). The critical-path method: Resources planning and scheduling. Industrial scheduling, 347-365.• Leach, L. P. (1999). Critical chain project management improves

project performance. Project Management Journal, 30, 39-51.• Maylor, Project Management. Chapter 7

References

• Maylor, H., 2010. Project Management. 4th Ed. Chester: Pearson.• MindTools, 2013. Critical Path Analysis and PERT Charts. [Online] Available at:

http://www.mindtools.com/critpath.html [Accessed on 07/11/13]• Margaret Rouse, 2011. Critical Path Method (CPM). [Online] Available at: http://

whatis.techtarget.com/definition/critical-path-method-CPM [Accessed on 07/11/13]• Tutorialspoint, 2013. Critical Path Method. [Online] Available at: http://

www.tutorialspoint.com/management_concepts/critical_path_method.htm [Accessed on 07/11/13]