All projects are carried out under constraints – traditionally cost, time and scope. These three important factors, commonly called the triple constraint, are often represented as a triangle (see figure 1). Each constraint forms the vertices with quality added as a central theme.
- Projects must be delivered within cost.
- Projects must be delivered on time.
- Projects must meet agreed scope, no more – no less.
- Projects must also meet customer quality requirements.
Figure 1: The triple constraint
More recently the triangle has given way to a project management diamond, with cost, time, scope and quality the four vertices with customer expectations as a central theme (see Figure 2). No two customer expectations are the same so you must ask what their expectations are.
Figure 2: The project management diamond
1. Cost: All projects have a finite budget; the money a customer is willing to spend delivering a new product or service. When you reduce the projects’ cost, you will either have to reduce its scope or increase its time.
2. Time (schedule): As the saying goes ‘time is money’, a commodity that slips away too easily. Most projects have a deadline date for delivery. When you reduce the projects’ time, you will either have to increase its cost or reduce its scope.
3. Scope: Many projects fail on this constraint because the full scope of the project is not fully defined or understood at the start. When you increase the projects’ scope, you will either have to increase its cost or time.
When a customer asks you to carry out a project they will usually say what is important, for example, the project must cost no more than £50k, be delivered on a particular date, or contain certain features.
The triple constraint is about balancing each constraint to reach a successful conclusion. As the project progresses, the project manager may find changes impact one or more of the constraints. So what might happen? Here are some examples:
1. During an automotive engineering project an unexpected budget cut is imposed on your project after the company posts poorer than expected 4th quarter results.
- Impact: Scope is cut, quality reduced and the schedule pushed out so cheaper resources can be made available. The most important constraint in this case is cost (the money the company is willing to spend).
2. During a project to create a new mobile phone handset, your customer asks to bring the launch date forward by two weeks to coincide with a major industry show.
- Impact: Costs increase as more people are added to meet the new deadline. Some features of the product are removed and put in a phase 2 release to reduce the delivery time and meet the new launch date. The most important constraint in this case is time (the project schedule).
3. During a software development project your customer increases the scope. They ask to add new features to the software after hearing about a competitors’ product that will be in direct competition with theirs. It is important the product has the new features if it is to compete successfully.
- Impact: The budget and schedule increase as a result pushing out the final delivery date. More people are added to the project to minimise disruption to the schedule increasing the projects’ overall cost. The most important constraint in this case is the scope (the features of the product).
In each of these examples the project manager needs to rebalance the project to meet the new constraints and deliver a success.
The adage ‘fast – cheap – good: you can have any two’, has more than a grain of truth. Rarely does a project manager find they have a budget to deliver top quality on time. More often the project manager needs to weigh one constraint against another to reach the best result.
As a project manager you need to educate your customers about the project management triple constraint, create the best balance and be aware of all changes that impact cost, time and scope.
The triple constraint represents the key elements of a project that when balanced well leads to success.
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