Resource Leveling and Resource Smoothing are two resource optimization techniques used in the Develop Schedule process, as defined in PMBOK® Guide, 6th Ed. PMP® and CAPM® certification aspirants often get confused between these terms. While Resource Leveling is explained quite well in the Guide, Resource Smoothing isn’t. In fact, Resource Smoothing doesn’t find a mention in most project management references. In this post, we’ll learn about the difference between the two with the help of examples and illustrations. If you been following my personal blog, then this is another post in the PMP Study Notes series.
Resource Leveling vs Resource Smoothing Quiz
Before we dive into the subject, let’s take a quick quiz to test your current understanding of this topic.
Difference between Resource Leveling and Resource Smoothing
Resource Leveling and Resource Smoothing are two resource optimization techniques. Resource Leveling is performed to balance the demand and supply of resources. Resource Smoothing is performed to achieve a more uniform resource utilization over a period of time. Resource Leveling may change the critical path of the project, whereas Resource Smoothing does not.
PMBOK® Guide Definitions
Resource Leveling: A technique in which start and finish dates are adjusted based on resource constraints with the goal of balancing demand for resources with the available supply. Resource Leveling may be performed:
- when key or shared resource are only available at certain times, or available in limited quantities, or over-allocated (as illustrated in Figure 6.20 of the Guide).
- to keep resource usage at a constant level (reduce fluctuation in demand for key resources).
Resource Smoothing: A technique which adjusts the activities of a schedule model such that the requirement for resources on the project do not exceed certain predefined resource limits. Resource Smoothing was introduced in the 5th Edition (2012). Most project management references mention only Resource Leveling.
I see some ambiguity with the PMBOK Guide definitions. First, what are “certain predefined resource limits”? The Guide doesn’t provide any example of this. Second, it says Resource Leveling may be performed to keep resource usage at a constant level. That sounds more like “smoothing”.
Let’s not spend more time delving into the theory, and understand these concepts from a practical point of view. The following illustration may help you wrap your head around these concepts easily.
Illustration of Resource Leveling and Resource Smoothing
Click on the image above to open it in a new window
The diagram shows a project with 6 activities. Assume that each box in the Gantt chart represents a time period of 1 month on the horizontal axis.
- The project cannot have more than 5 resources at any point (predefined resource limit).
- Only 4 resources are available to work on Activity D at any point (scarce resources).
The diagram shows 3 steps.
1. Apply Critical Path Method
In the first step, the schedule is analyzed with the Critical Path Method (CPM). A-C-D-F is determined to be the Critical Path of the project. Activities B and E have some float, which is represented in gray. Activity D is utilizing more than 4 resources in some months (violating constraint 2).
2. Apply Resource Leveling
In the second step, Resource Leveling is performed. Since only 4 resources are available to work on Activity D, which is on the Critical Path, we need to extend the activity duration to reduce resource usage each month, which further results in increase in the Critical Path duration by 1 month.
3. Apply Resource Smoothing
In the third step, Resource Smoothing is performed to meet the predefined resource limit of 5 resources at any point during the project.
Finally we end up with a resource optimized schedule that meets both the resource constraints.
Let’s review the quiz answers. Go ahead and review the 3 questions again. By now, you should be able to answer all the questions correctly.
Answer 1: In this case, the coding activity has a float and hence not on the Critical Path. The activity has a predefined resource limit of 6 developers per month. This is a case for Resource Smoothing.
Answer 2: Richard, a key resource, is over-allocated (150% allocation). That makes it case for Resource Leveling. A software tool may help with resource leveling, but that’s not the best answer among the given choices.
Answer 3: Jack is a scarce resource for the project and his availability is constrained. The project schedule had to be extended to work with the constraint. This is also an example of Resource Leveling.
The following table summarizes the difference between Resource Leveling and Resource Smoothing.
|Aims to balance resource demand / supply|
|May alter (usually increase) the critical path|
|Usually performed after applying CPM, but before Resource Smoothing|
|Deals with critical resources|
|Critical resources are the primary constraint|
|Reasons to perform - key resources are only available at certain times, or in limited quantities, or over allocated|
|Aims to achieve uniform resource utilization|
|Doesn’t change the critical path; resource demand is smoothened (evened out) by utilizing activity float|
|Usually performed after Resource Leveling|
|Deals with non-critical resources|
|Project duration is the primary constraint|
|Reasons to perform - limits on resource usage, or uneven resource utilization|
I hope you found this post useful. Please share your feedback via the comments section below and share this post with those who can benefit from it.
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