The Triple Constraint

Written By:  Mark A. Frasher; May 14, 2017

The triple constraint is often described as the iron triangle.  This triangle analogy is reference to the inter-related constraints of Time, Cost, and Scope.  This emphasizes the importance of managers and their role in managing constraints, with a focus on the fact that all threats to a project are not necessarily in a project manager’s control.  Finally, the author identifies a new triangle, the “Management Constraint Triangle” as a tool to use in the daily life of a project manager to better manage project constraints.


What Are Constraints?

Before analyzing the triangle of management constraints, it is important to first identify constraints, and to also spend some time analyzing the triple constraints of time, cost, and scope. 

"A constraint, as identified by the PMBOK Guide, 5th edition, is a limiting factor that affects the execution of a project, program, or process."

A time constraint, therefore, is a reference to any project constraints that are related to time, i.e., the schedule.  A cost constraint, similarly, is any constraint that is related to cost, i.e., the budget.  And finally, the scope constraint, is any constraint that impacts the scope of the project, i.e., an over-sized project that results in “scope creep”.

Since a project is a unique and temporary endeavor, there are always limited resources.  Limited resources (time, cost, etc.) are at the cornerstone of what must be managed on a project and is where the concepts of constraints were born. 

One of a project manager’s primary duties is to manage the project to a high degree of quality.  In order to do this, the project manager must have a solid understanding of constraints and how they affect the outcome, or quality, of a project.  Knowing this, it is vital that the manager also understand the relationships between constraints and the impact they have on one another.


The Triple Constraint & Constraint Relationships

The three constraints of time, cost, & scope are inter-related and often affect one another.  When one or more of the constraints is realized, and the project is negatively affected, the result is typically a project that is out of scope and can be considered to be poor quality. 

Usually, when people think of quality, they think in terms of product quality or the quality of the projects deliverable.  However, as a project manager, quality must also include completing the project on time, on or under budget, and within scope.  Anything else is a project that did not meet its required outcome, and therefore is out of scope, which is by definition, poor quality.

The primary concern that many established project managers and scholars have with the traditional analysis of the triple constraint is that it is not enough to assess the competing demands of a project in its totality.  Project managers often face risk and work in a space of uncertainty. 

Competing demands such as risk, resources, stakeholders, and personnel often complicate a project and can also affect the time cost and scope of a project.  If a project manager were to focus more broadly on suggested constraint concepts, they would be more adept at recognizing the relationships between risks and constraints and would be better positioned to deliver a high-quality project than if they were to only focus on time, cost, and scope.

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