Activity Network Diagrams and Critical Path Mapping

Activity network diagram--a proven method of showcasing the timelines of various subtasks involved in a specific project, enables the calculation of the entire task duration as well as the start and finish timeframes for each task. Along with depicting those subtasks that are critical for on-time task completion, the activity network diagram also determines the areas where extra efforts for speeding subtasks results in the greatest payoff towards overall speed. In the 1950s, the technique had emerged as PERT-- Program Evaluation Research Technique and CPM- Critical Path Method, and boasts of several ways of representing the output.
Here we review the arrow/ activity-on-arrow diagram that encompasses numbered nodes as the instantaneous stop/start touch-points for activities, which are shown as taking place on the arrows that connect the nodes.
Activity Network Diagram
The diagram shows which activities/series of activities is critical for the timing of complicated interactive activities; and is helpful in deciding when and where to apply extra energy for completing projects on time. Mostly used for coordinating complex subtasks/ tasks with simultaneous paths and durations with relative certainty, the diagram comes in handy where there is little or no margin for timing errors. Critical path mapping serves to be invaluable in project bounding, measuring and improving upon the different phases involved with Lean Six Sigma methodology.
Creation of Activity Network Diagrams
  • The right team, with personal or connected knowledge about the timing of various subtasks, including managers and those employees who happen to be proximate to the real situation, have to be assembled. 
  • Brainstorming session or assimilation of the list of tasks from similar previous projects helps in the identification of all the subtasks necessary for completing the overall project. These activities are linked with paths or strings that follow each other and often describe the sequences of activities which take place alongside. Once all activities are located in some path/string of activities, an overall sequence has to be created by connecting the paths. These connections depict the areas where jobs/tasks require inputs from parallel sequences, prior to the beginning of the next task. All missing and duplicate tasks are taken care of at this stage.
  • Estimated time duration is assigned to each task/job. As these times have to be added, it’s good to keep their numbers consistent, instead of having days, hours or minutes for completion. Thereafter, the Lowest Common Denominator is selected. The shortest possible time in which the overall task is capable of being completed is calculated by aggregating the time of each subtask; this in turn results in the path of longest cumulative duration or the critical path. 
  • Knowledge about the critical path is essential as it predicts if the time objectives linked with a specific project are attainable and identifies those jobs/tasks which have no slack. For the timely completion of any project, all these tasks have to remain on schedule. The diagram also identifies the targeted areas that require improvements for better speed and shortening of the overall time duration.
  • The earliest as well as the latest starting/finishing times are determined for each job or subtask in a specific project. The earliest starting time for any job is calculated as the cumulative duration of the previous jobs located on that path. The earliest finishing time is merely the earliest start time added to the duration of a task. The process is repeated for each job present on all the paths, until the final finish point is reached. The latest start /finish times are then calculated by beginning with the earliest finishing time located at the last part of the diagram.
  • The slack time for a job/task can be calculated by subtracting the earliest starting time from the latest starting time. By definition, all the tasks present on the critical path possess zero slack time. 
Once the activity network diagram is completed, it is well advised to review the same with all individuals involved with the work described by the same. The diagram can be expanded or modified as required to fit actual situations. Serving as a time-map of time-sensitive projects, the diagram keeps project timelines on track and restricts the team to the critical path, both manually and through automated means. 
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