Critical Path Method

Critical Path Method History

Critical Path Method History can be traced back as far as 5,000 years ago, during the building of the pyramids.
Critical Path Method, more popularly known as CPM, is a project planning technique. The Critical Path Method, tries to optimize the sequence of scheduled activities within a project. CPM makes sure that the project will be completed on time.

We all do basic planning before starting any task, though not using defined techniques. We estimate:

  • average number of hours required for the total work
  • break down the complex task into smaller tasks to check whether we can complete the work as required.

Thus, the Critical Path Method or any other project planning tool is not something entirely new. The origins of all project planning techniques including CPM can be traced to ancient civilizations.

Critical Path Method History – Great Pyramids

The Great Pyramid of Giza in Egypt were built over 5000 years back. Construction used about two million blocks of stone and thousands of skilled workers. Ancient Egyptian records of that period prove that there were four faces for the pyramid and the workers were organized into four construction teams to proceed simultaneously. It took 20 years to complete the construction which demanded sophisticated planning and organization.

Gantt Chart

Modern project planning tools were introduced in mid 1900s. American mechanical engineers Frederick Taylor and Henry Gantt came up with a graphic method for planning, controlling and tracking a work schedule which became popular as Gantt charts.

Gantt charts are still used widely because of its simplicity. But Gantt chart does not depict the interrelationships between the activities or the constraints they impose on each other.

The development of the Critical Path Method was a joint venture between Remington Rand Univac, a computer company and the DuPont, a chemical company. Two mathematicians, Morgan Walker and James Kelly, were looking at methods to avoid the costs of plant restarts and shutdowns resulted due to inefficient scheduling. They found that money could be saved if right tasks are performed at right time. They devised CPM to deal with the interrelationships of separate activities within a project schedule and could save DuPont 25 percent on shutdowns.

Graphically Project View

CPM represents the project graphically and predicts its completion time. The critical path is a sequence of individual activities of a project which must be finished on schedule to finish the whole project on time. This method was first tested on a project to build a chemical plant in 1958 and again during the maintenance shutdown of another plant at Kentucky in 1959.

In 1958, the US Navy along with Lockheed Missile Systems, an aerospace company and Booz Allen & Hamilton, a consultancy firm devised another technique called Program Evaluation Review Technique (PERT). Like CPM, PERT was also designed to deal with the interrelationship between different activities in a project. James Kelly who was involved in CPM project attributed the term “critical path” to the developers of PERT.

Theory of Constraints

In the 1980s, Israeli physicist Eliyahu Goldratt developed the Theory of Constraints as an improvement to CPM. The original CPM did not consider that a critical path may change during the project. As per the Theory of Constraints, the improvement of a project and its schedule depends on the identification of the constraint that a system can never be better than its weakest part. The Critical Path Method is commonly used for projects in

  • construction,
  • software development
  • defense
  • aerospace
  • product development
  • plant maintenance
  • engineering

The Critical Path Method is effective in any project with interdependent activities.

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