Iron Triangle

The Iron Triangle. Source: Wright and Lawlor-Wright 2019, fig. 1.1.
The Iron Triangle. Source: Wright and Lawlor-Wright 2019, fig. 1.1.

The Iron Triangle is essentially a model/framework for project management. The three sides or vertices of the triangle are cost, time and scope. Scope is often substituted in literature with quality. Some see quality as the outcome of the other three.

Project managers can make trade-offs among these three factors to delivery a quality product. The triangle is called "iron" because the factors specify hard and tightly integrated constraints. Changing any one will affect the others.

When projects adopted Agile methodologies from the early 2000s, the Iron Triangle was found to have limitations. Many variations have been proposed to cater to modern project management practices.

The Iron Triangle has also been called the Project Management Triangle or the Triple Constraint Model.

Discussion

  • What are the three constraints that form the Iron Triangle?
    The Iron Triangle explained. Source: TeamGantt 2021.

    The triple constraints specify project deadline, the allocated budget/resources and what features should go into the product. When applied correctly, the triangle produces its fourth element, quality. In one interpretation, scope consists of quality, standards and specifications. Performance and requirements are suggested alternatives to scope.

    The model can help project managers take decisions when responding to changes. For example, if deadline can't be modified and scope increases, manager can add more resources. Instead, if budget is fixed, manager must be ensure that scope doesn't increase. She must monitor progress so that the project is delivered on time.

    The triangle also help project managers to communicate clearly with clients. Impact of changes can be described in the language of these constraints. Internally, the triangle may help convince management to approve extra budget. Risks can be managed better with forward planning.

    Quality may be defined as fitness for purpose or meeting requirements. While time and cost are easy to measure, quality isn't. Quality management therefore requires special attention and expertise.

  • As a project manager, how can I apply the Iron Triangle?
    Project priority matrix. Source: Dalcher 2014, fig. 2.4.
    Project priority matrix. Source: Dalcher 2014, fig. 2.4.

    There's not much a project manager can do if all constraints are fixed. To make changes, it helps to keep at least one constraint flexible. This must be negotiated at the outset. The figure shows an example using the project priority matrix, a tool that managers can use. This example makes performance/scope/quality non-negotiable. We can accept higher cost so that product can be released early.

    Clarify with client what features are essential. This prioritization can help adjust scope if needed. Budget can be increased for essential features should costs rise.

    Along with the project management plan, proactively create a risk management plan. This would detail how the constraints would be adjusted at the onset of a risk. Be clear about when such a plan will be triggered. Likewise, have a change management plan that details roles, processes, approvals, tools, etc.

    Before applying the Iron Triangle (or alternative models), it's helpful to understand the project. One size doesn't fit all. Each project type needs its own management style. The NTCP Framework might help to classify projects.

  • How does the Iron Triangle change for Agile?
    Iron Triangle in Waterfall versus Agile methodologies. Source: Aljaber 2024.
    Iron Triangle in Waterfall versus Agile methodologies. Source: Aljaber 2024.

    In Waterfall, scope is fixed while time and resources vary. In Agile, the opposite is true: scope varies while the other two stay fixed. By making time fixed, the project promises regular and timely deliveries. This can be through Scrum sprints or Kanban WIP limits. This iterative process also allows the team to respond faster to customer feedback. By making resources fixed, higher productivity is achieved since team members are already familiar with processes and interactions. With each iteration, high-level requirements are refined with more details and then prioritized. These feed into the schedule. Thus, scope is a variable.

    Highsmith criticized this inverted triangle and proposed an alternative called the Agile Triangle. It consists of value, quality and constraints. Scope, time and cost of the original triangle get subsumed under constraints. As the product evolves continuously and adapts to changing requirements, quality must be maintained. Product must provide value to customers. Rajeev Singh later commented that value must be achieved not just for customers but also for employees (empowerment, leadership, mentorship).

  • Does meeting the triple constraints lead to success?
    Project Status Model (PSM) of the movie Titanic. Source: Bronte-Stewart 2015, fig. 4.
    Project Status Model (PSM) of the movie Titanic. Source: Bronte-Stewart 2015, fig. 4.

    For years, a project that was delivered on time, in scope and within budget was deemed a success. Despite this, some projects failed in the long term. Examples include the Tacoma Narrows Bridge and Motorola's Iridium satellite project. On the contrary, there are also many projects that attained long-term success even when they were perceived as failures under the triple constraints model. Example are the movie Titanic and Airbus A380.

    Project success is not the same as project management success. Project success is about satisfying stakeholders and achieving strategic goals. Iron Triangle may lead us to short-term success but not necessarily long-term success. Beyond the triple constraints, we should look at value creation.

    Indicators of success go beyond the triple constraints. Some of these are innovation, risk management, requirements change management, product acceptance, sustainable practices, customer satisfaction, and process improvement. One study identified nine themes: project efficiency, program efficiency, portfolio efficiency, organizational business results, teamwork, individual development, PMO development, performance management system for increased readiness, and systems thinking.

  • How relevant are soft skills to project success?
    The soft pyramid with the iron triangle. Source: Caccamese and Bragantini 2013, fig. 5.
    The soft pyramid with the iron triangle. Source: Caccamese and Bragantini 2013, fig. 5.

    The traditional Iron Triangle is really about "hard skills" such as effort estimation, cost control and task scheduling. Some managers have considered soft skills but in an ad hoc manner. The impact of soft skills on project has been underestimated. While PMBOK considers soft skills, they're not treated as operating in a constrained environment.

    One model includes soft factors as sides of a pyramid, its triangular base representing the original Iron Triangle. Soft factors are the following:

    • Motivational (ABV): Individual motivation. Eg. working conditions, career growth, rewarding systems.
    • Social (ACV): Protocols for acceptable behaviour. Eg. punctuality, timely responses, honesty, respecting consensus.
    • Analytic/Holistic (BCV): Individual thinking. Eg. analysis/synthesis, linear/nonlinear, sequential/parallel, assertive/cooperation.

    Like hard factors, soft factors are also constrained by context, project and organization. Trade-offs are needed with soft spaces as well. Giving individuals high autonomy (analytic/holistic) might require stricter reporting, sharing and coordination (social). In a professional association, individual excellence (analytic/holistic) must be balanced with a sense of belonging (motivational).

  • What are some variations of the Iron Triangle?
    Variations of the Iron Triangle. Source: Adapted from Vahidi and Greenwood 2009.
    Variations of the Iron Triangle. Source: Adapted from Vahidi and Greenwood 2009.

    Marasco's Project Pyramid includes scope, time, quality and resources. Trade-offs can be done by calculating the pyramid's volume. Haughey's Project Management Diamond includes cost, time, quality and scope. PMI's Six-Point Star Model adds risk, schedule and resources to the traditional triple constraints. To address sustainability, there's the Star Model that includes economical, environmental, time, quality and social.

    The Value Triple Constraint focuses on value. Value is a function of project scope and process capability. Value is calculated from quantified benefits and costs. The latter encompass cost and time from the original triangle. Treating time as cost allows this model to account for inter-project interactions. Highsmith's Agile Triangle also gives importance to value. Value makes us ask why we're building the product.

    Yet another model considers investment, return on investment and the cost of delay. Product features should be treated as adding business value. Scope creep isn't a problem when it adds value.

Milestones

1960

Scheduling is given due attention only in the 1960s. The Industrial Revolution of the 18th century laid down precise processes for scope and cost control, but not scheduling. In fact, project management as a discipline emerged only in the 20th century.

1969

Martin Barnes invents the Iron Triangle as a way to manage contracts (the word "projects" isn't used at this time). Soon after, quality is replaced with performance. Years later (in 2012) Barnes noted that the triangle came about because no one was looking at quality/performance, though there were engineers looking at cost and time.

1975

Brooks publishes a book titled The Mythical Man-Month. One of the insights is that adding more people to a delayed project delays it further. New members need time to get familiar with the project. There's also an increased overhead of communication amongst more team members. This insight challenges the cost-time trade-offs in the Iron Triangle.

1987

The Project Management Institute (PMI) publishes the The Project Management Body of Knowledge (PMBOK). This describes eight knowledge areas including scope, time and cost. Later editions of this document are renamed as the PMBOK® Guide. However, this guide doesn't use the terms "iron triangle" or "triple constraints".

2000

The Agile movement starts in the early 2000s. Stakeholders demand adaptability but this makes it hard to meet the predictability of the Iron Triangle. Agile projects are being ill-judged with traditional metrics set by the Iron Triangle. This failure motivates the use of "soft metrics" such as quality, risk, technology, human relations, stakeholder management, communications and leadership.

2005

Studies around the mid-2000s show that many project managers use the Iron Triangle. When faced with time/cost overruns and complex projects, managers tend to rely more on the model. The enduring popularity of the model maybe due to its simplicity.

2009
The Agile Triangle. Source: Highsmith 2023.
The Agile Triangle. Source: Highsmith 2023.

Highsmith introduces the Agile Triangle comprised of value, quality and constraints. The original Iron Triangle determines the constraints within which value and quality must be achieved. He cites the movie Titanic as an example. It was considered a failure within the Iron Triangle since it was delayed and over budget; but it's a success going by the Agile Triangle since it delivered value.

2015

NEC Contracts in the UK establishes the NEC Awards to recognize excellence in project delivery. In 2022, this is renamed as Martin Barnes Awards, in honour of the creator of the Iron Triangle.

References

  1. APM. 2022. "A tribute to APM founder, Dr Martin Barnes CBE." News, APM, February 11. Accessed 2024-02-08.
  2. Aljaber, T. 2024. "Iron triangle project management and agile." Atlassian. Accessed 2024-02-08.
  3. Baratta, A. 2006. "The Triple Constraint, A Triple Illusion." PMI Global Congress—Seattle, Washington. Accessed 2024-02-08.
  4. Barnes, M. 2006. "How it all began." PM World Today, July. Accessed 2024-02-08.
  5. Barnes, M. 2007. "Some Origins of Modern Project Management: A Personal History." PM World Today, vol. II, no. XI, November. Accessed 2024-02-08.
  6. Bronte-Stewart, M. 2015. "Beyond the Iron Triangle: Evaluating Aspects of Success and Failure using a Project Status Model." In: Usoro, A. (ed), Computing and Information Systems Journal, vol. 19, no. 2, pp. 19-36. Accessed 2024-02-08.
  7. Caccamese, A. and C. Bragantini. 2013. "Beyond The Iron Triangle: Year Zero." PM World Journal, vol. II, no. XII, December. Accessed 2024-02-08.
  8. Dalcher, D. 2014. "Rethinking Success in Software Projects: Looking Beyond the Failure Factors." In: Ruhe, G. and C. Wohlin (eds), Software Project Management in a Changing World, Springer, Berlin, Heidelberg. doi: 10.1007/978-3-642-55035-5_2. Accessed 2024-02-08.
  9. Davidson, J. 2013. "Blow up the Iron Triangle: Rethinking Software Project Approaches and Goals to Increase Business Value." PM World Journal, vol. II, no. XII, December. Accessed 2024-02-08.
  10. Goodman, R. 2005. "The ascent of risk: risk and the Guide to the project management body of knowledge (PMBOK guide), 1987-1996-2000-2004." PMI® Global Congress 2005—Asia Pacific, Singapore. Accessed 2024-02-08.
  11. GovHK. 2022. "Works departments receive Martin Barnes Awards in UK." Press release, Govt. of Hong Kong, June 22. Accessed 2024-02-08.
  12. Highsmith, J. 2023. "The ghosts of project management's Iron Triangle still haunt agile teams." LinkedIn Pulse, May 10. Accessed 2024-02-08.
  13. Kim, D. 2012. "The Agile Triangle." Blog, ProjectManagement.com, May 14. Accessed 2024-02-08.
  14. NEC Contracts. 2024. "NEC Awards." NEC Contracts. Accessed 2024-02-08.
  15. Orhof, O., A. Shenhar, and D. Dori. 2013. "A Model-Based Approach to Unifying Disparate Project Management Tools for Project Classification and Customized Management." INCOSE International Symposium, vol. 23, no. 1, pp. 960–972. doi: 10.1002/j.2334-5837.2013.tb03066.x. Accessed 2024-02-08.
  16. PMI. 2013. "A Guide to the Project Management Body of Knowledge (PMBOK® Guide)." Fifth Edition, Project Management Institute. Accessed 2024-02-08.
  17. Pollack, J., J. Helm, and D. Adler. 2018. "What Is the Iron Triangle, and How Has It Changed?" International Journal of Managing Projects in Business, vol. 11, no. 2, pp. 527-547. Accessed 2024-02-08.
  18. Rahschulte, T. J. and K. Milhauser. 2010. "Beyond the triple constraints: nine elements defining project success today." PMI Global Congress—North America, Washington, DC. Accessed 2024-02-08.
  19. Rudder, A. and K. Main. 2023. "What Is The Project Management Triangle?" Forbes, July 20. Accessed 2024-02-08.
  20. Singh, R. 2012. "A Case for Enhancing the Agile Triangle." Blog, Agile Montage, January 17. Accessed 2024-02-08.
  21. Smart, J. F. and J. Molak. 2016. "The Project Management Triangle must die!" LinkedIn Pulse, April 16. Accessed 2024-02-08.
  22. TeamGantt. 2021. "Triple Constraint Project Management Explained." TeamGantt, on YouTube, November 18. Accessed 2024-02-08.
  23. Vahidi, R. and D. Greenwood. 2009. "Triangles, tradeoffs and success: a critical examination of some traditional project management paradigms." CIB Joint International Symposium - Construction Facing Worldwide Challenges, Dubrovnik, pp. 927-936, September 27-30. Accessed 2024-02-08.
  24. Weaver, P. 2007. "The Origins of Modern Project Management." Fourth Annual PMI College of Scheduling Conference, Vancouver, April 15-18. Accessed 2024-02-08.
  25. Wikipedia. 2023. "The Mythical Man-Month." Wikipedia, November 12. Accessed 2024-02-08.
  26. Wright, A. and T. Lawlor-Wright. 2019. "Project success and quality: balancing the iron triangle." Routledge, Taylor & Francis, Abingdon, UK. Accessed 2024-02-08.

Further Reading

  1. Barnes, M. 2006. "How it all began." PM World Today, July. Accessed 2024-02-08.
  2. Dalcher, D. 2014. "Rethinking Success in Software Projects: Looking Beyond the Failure Factors." In: Ruhe, G. and C. Wohlin (eds), Software Project Management in a Changing World, Springer, Berlin, Heidelberg. doi: 10.1007/978-3-642-55035-5_2. Accessed 2024-02-08.
  3. Rudder, A. and K. Main. 2023. "What Is The Project Management Triangle?" Forbes, July 20. Accessed 2024-02-08.
  4. Ebbesen, J. B. and A. J. Hope. 2013. "Re-imagining the Iron Triangle: Embedding Sustainability into Project Constraints." PM World Journal, vol. II, no. III, March. Accessed 2024-02-08.
  5. Abdulhafedh, A. 2022. "The Diamond Framework Model as an Effective Tool for Project Management." International Journal of Management and Commerce Innovations, vol. 9, no. 2, pp. 529-536, October 2021 - March 2022. Accessed 2024-02-08.

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