History of the Critical Path Method

Since it was first designed in 1957, the critical path method has become an important way that business owners or project managers can oversee large undertakings. It encourages efficiency by dividing complicated efforts into a series of small tasks with costs and resources associated with each, and its development allows managers to see where potential breakdowns might occur and what resources are available to deal with them if that happens.

The benefit of using the critical path method for the project manager is that it’s an effective way to see which delays can be handled with built-in slack time -- the “float” -- and which will cause a project to fall behind schedule. Since there is no float on the critical path by definition, if a deadline is set in stone it means that the manager has to take steps to get everything back on schedule. In some cases, activities can be pruned or performed in parallel, which is known as “fast tracking,” and in some cases, added resources shrink the amount of time needed to complete tasks along the way, known as “crashing.”

The critical path method was developed at the DuPont Company in 1957 by a pair of mathematicians who were looking at ways to avoid the costs of plant shutdowns and restarts caused by inefficient scheduling. Their research showed that money could be saved by focusing efforts on performing the right tasks at the right times, rather than flooding the problem with labor to stay on schedule. This saved DuPont 25 percent on shutdowns, and James Kelley and Morgan Walker published the first paper on their findings in 1959. Ironically, DuPont then dropped the CPM system when the management team responsible for it changed.

Although CPM at DuPont was fading, Mauchly Associates picked it up. Beginning in 1959, the company helped commercialize CPM by focusing on scheduling efficiencies rather than cost savings, organizing CPM training and transforming it into a new way of doing business for construction companies. Catalytic Construction bought into the concept in 1961, and several others quickly followed. Because of the primitive nature of computer systems at that time, the cost of the process was a barrier to entry.

In addition to its ability to reduce the complexity of larger projects by breaking them into component tasks, the critical path method became popular because of the innovations in computer hardware and software. In the first few decades of the critical path method, the tools were bulky mainframe computers used by specialists who often required months of training. The PC revolution brought scheduling management software to the desktop, and the rise of computer networking allowed the results to be shared easily among team members.

Several other program management tools have been developed to increase the effectiveness of the critical path method. The Program Evolution and Review Technique, or PERT, developed by the U.S. Navy around the same time that the DuPont mathematicians were hard at work, has a similar purpose in estimating the time it takes to complete specific tasks, but PERT is based on probability rather than offering an absolute time. Coming out of the same project, the Work Breakdown Structure dividing a project into deliverables and tasks was instituted by the Department of Defense in 1962. In 1984, the Theory of Constraints, which introduces the concept of constraints and the need to restructure an organization around them, was introduced by Eliyahu M. Goldratt and later expanded into critical chain program management.